This section describes the XML format used to represent domains, there are variations on the format based on the kind of domains run and the options used to launch them. For hypervisor specific details consult the driver docs
The root element required for all virtual machines is
named domain. It has two attributes, the
type
specifies the hypervisor used for running
the domain. The allowed values are driver specific, but
include "xen", "kvm", "qemu" and "lxc". The
second attribute is id which is a unique
integer identifier for the running guest machine. Inactive
machines have no id value.
<domain type='kvm' id='1'>
<name>MyGuest</name>
<uuid>4dea22b3-1d52-d8f3-2516-782e98ab3fa0</uuid>
<genid>43dc0cf8-809b-4adb-9bea-a9abb5f3d90e</genid>
<title>A short description - title - of the domain</title>
<description>Some human readable description</description>
<metadata>
<app1:foo xmlns:app1="http://app1.org/app1/">..</app1:foo>
<app2:bar xmlns:app2="http://app1.org/app2/">..</app2:bar>
</metadata>
...
namename element provides
a short name for the virtual machine. This name should
consist only of alpha-numeric characters and is required
to be unique within the scope of a single host. It is
often used to form the filename for storing the persistent
configuration file. Since 0.0.1uuiduuid element provides
a globally unique identifier for the virtual machine.
The format must be RFC 4122 compliant,
eg 3e3fce45-4f53-4fa7-bb32-11f34168b82b.
If omitted when defining/creating a new machine, a random
UUID is generated. It is also possible to provide the UUID
via a sysinfo
specification. Since 0.0.1, sysinfo
since 0.8.7genidgenid
element can be used to add a Virtual Machine Generation ID which
exposes a 128-bit, cryptographically random, integer value identifier,
referred to as a Globally Unique Identifier (GUID) using the same
format as the uuid. The value is used to help notify
the guest operating system when the virtual machine is re-executing
something that has already executed before, such as:
The libvirt XML parser will accept both a provided GUID value or just <genid/> in which case a GUID will be generated and saved in the XML. For the transitions such as above, libvirt will change the GUID before re-executing.
titletitle provides space for a
short description of the domain. The title should not contain
any newlines. Since 0.9.10.descriptiondescription element provides a
human readable description of the virtual machine. This data is not
used by libvirt in any way, it can contain any information the user
wants. Since 0.7.2metadatametadata node can be used by applications
to store custom metadata in the form of XML
nodes/trees. Applications must use custom namespaces on their
XML nodes/trees, with only one top-level element per namespace
(if the application needs structure, they should have
sub-elements to their namespace
element). Since 0.9.10There are a number of different ways to boot virtual machines each with their own pros and cons.
Booting via the BIOS is available for hypervisors supporting full virtualization. In this case the BIOS has a boot order priority (floppy, harddisk, cdrom, network) determining where to obtain/find the boot image.
... <os firmware='efi'> <type>hvm</type> <loader readonly='yes' secure='no' type='rom'>/usr/lib/xen/boot/hvmloader</loader> <nvram template='/usr/share/OVMF/OVMF_VARS.fd'>/var/lib/libvirt/nvram/guest_VARS.fd</nvram> <boot dev='hd'/> <boot dev='cdrom'/> <bootmenu enable='yes' timeout='3000'/> <smbios mode='sysinfo'/> <bios useserial='yes' rebootTimeout='0'/> </os> ...
firmwarefirmware attribute allows management
applications to automatically fill <loader/>
and <nvram/> elements and possibly enable
some features required by selected firmware. Accepted values are
bios and efi./usr/share/qemu/firmware/etc/qemu/firmware$XDG_CONFIG_HOME/qemu/firmwaredocs/interop/firmware.json in QEMU
repository. Regular users do not need to bother.
Since 5.2.0 (QEMU and KVM only)efi when the guest
uses UEFI, and it is not set when using BIOS.
Since 5.3.0 (VMware ESX and Workstation/Player)
typetype element specifies the
type of operating system to be booted in the virtual machine.
hvm indicates that the OS is one designed to run
on bare metal, so requires full virtualization. linux
(badly named!) refers to an OS that supports the Xen 3 hypervisor
guest ABI. There are also two optional attributes, arch
specifying the CPU architecture to virtualization,
and machine referring
to the machine type. The Capabilities XML
provides details on allowed values for
these. If arch is omitted then for most hypervisor
drivers, the host native arch will be chosen. For the test,
ESX and VMWare hypervisor drivers, however,
the i686 arch will always be chosen even on an
x86_64 host. Since 0.0.1loaderloader tag refers to a firmware blob,
which is specified by absolute path,
used to assist the domain creation process. It is used by Xen
fully virtualized domains as well as setting the QEMU BIOS file
path for QEMU/KVM domains. Xen since 0.1.0,
QEMU/KVM since 0.9.12 Then, since
1.2.8 it's possible for the element to have two
optional attributes: readonly (accepted values are
yes and no) to reflect the fact that the
image should be writable or read-only. The second attribute
type accepts values rom and
pflash. It tells the hypervisor where in the guest
memory the file should be mapped. For instance, if the loader
path points to an UEFI image, type should be
pflash. Moreover, some firmwares may
implement the Secure boot feature. Attribute
secure can be used then to control it.
Since 2.1.0nvramqemu.conf. If needed, the template
attribute can be used to per domain override map of master NVRAM stores
from the config file. Note, that for transient domains if the NVRAM file
has been created by libvirt it is left behind and it is management
application's responsibility to save and remove file (if needed to be
persistent). Since 1.2.8bootdev attribute takes one of the values "fd", "hd",
"cdrom" or "network" and is used to specify the next boot device
to consider. The boot element can be repeated multiple
times to setup a priority list of boot devices to try in turn.
Multiple devices of the same type are sorted according to their
targets while preserving the order of buses. After defining the
domain, its XML configuration returned by libvirt (through
virDomainGetXMLDesc) lists devices in the sorted order. Once sorted,
the first device is marked as bootable. Thus, e.g., a domain
configured to boot from "hd" with vdb, hda, vda, and hdc disks
assigned to it will boot from vda (the sorted list is vda, vdb, hda,
hdc). Similar domain with hdc, vda, vdb, and hda disks will boot from
hda (sorted disks are: hda, hdc, vda, vdb). It can be tricky to
configure in the desired way, which is why per-device boot elements
(see disks,
network interfaces, and
USB and PCI devices sections below) were
introduced and they are the preferred way providing full control over
booting order. The boot element and per-device boot
elements are mutually exclusive. Since 0.1.3,
per-device boot since 0.8.8
smbiosmode attribute must be specified, and is either
"emulate" (let the hypervisor generate all values), "host" (copy
all of Block 0 and Block 1, except for the UUID, from the host's
SMBIOS values;
the
virConnectGetSysinfo call can be
used to see what values are copied), or "sysinfo" (use the values in
the sysinfo element). If not
specified, the hypervisor default is used.
Since 0.8.7
Up till here the BIOS/UEFI configuration knobs are generic enough to
be implemented by majority (if not all) firmwares out there. However,
from now on not every single setting makes sense to all firmwares. For
instance, rebootTimeout doesn't make sense for UEFI,
useserial might not be usable with a BIOS firmware that
doesn't produce any output onto serial line, etc. Moreover, firmwares
don't usually export their capabilities for libvirt (or users) to check.
And the set of their capabilities can change with every new release.
Hence users are advised to try the settings they use before relying on
them in production.
bootmenuenable attribute can be either "yes" or "no".
If not specified, the hypervisor default is used.
Since 0.8.3
Additional attribute timeout takes the number of milliseconds
the boot menu should wait until it times out. Allowed values are numbers
in range [0, 65535] inclusive and it is ignored unless enable
is set to "yes". Since 1.2.8
biosuseserial with possible
values yes or no. It enables or disables
Serial Graphics Adapter which allows users to see BIOS messages
on a serial port. Therefore, one needs to have
serial port defined.
Since 0.9.4.
Since 0.10.2 (QEMU only) there is
another attribute, rebootTimeout that controls
whether and after how long the guest should start booting
again in case the boot fails (according to BIOS). The value is
in milliseconds with maximum of 65535 and special
value -1 disables the reboot.
Hypervisors employing paravirtualization do not usually emulate
a BIOS, and instead the host is responsible to kicking off the
operating system boot. This may use a pseudo-bootloader in the
host to provide an interface to choose a kernel for the guest.
An example is pygrub with Xen. The Bhyve hypervisor
also uses a host bootloader, either bhyveload or
grub-bhyve.
... <bootloader>/usr/bin/pygrub</bootloader> <bootloader_args>--append single</bootloader_args> ...
bootloaderbootloader element provides
a fully qualified path to the bootloader executable in the
host OS. This bootloader will be run to choose which kernel
to boot. The required output of the bootloader is dependent
on the hypervisor in use. Since 0.1.0bootloader_argsbootloader_args element allows
command line arguments to be passed to the bootloader.
Since 0.2.3
When installing a new guest OS it is often useful to boot directly from a kernel and initrd stored in the host OS, allowing command line arguments to be passed directly to the installer. This capability is usually available for both para and full virtualized guests.
...
<os>
<type>hvm</type>
<loader>/usr/lib/xen/boot/hvmloader</loader>
<kernel>/root/f8-i386-vmlinuz</kernel>
<initrd>/root/f8-i386-initrd</initrd>
<cmdline>console=ttyS0 ks=http://example.com/f8-i386/os/</cmdline>
<dtb>/root/ppc.dtb</dtb>
<acpi>
<table type='slic'>/path/to/slic.dat</table>
</acpi>
</os>
...
typeloaderkernelinitrdcmdlinedtbacpitable element contains a fully-qualified path
to the ACPI table. The type attribute contains the
ACPI table type (currently only slic is supported)
Since 1.3.5 (QEMU)
Since 5.9.0 (Xen)
When booting a domain using container based virtualization, instead
of a kernel / boot image, a path to the init binary is required, using
the init element. By default this will be launched with
no arguments. To specify the initial argv, use the initarg
element, repeated as many time as is required. The cmdline
element, if set will be used to provide an equivalent to /proc/cmdline
but will not affect init argv.
To set environment variables, use the initenv element, one
for each variable.
To set a custom work directory for the init, use the initdir
element.
To run the init command as a given user or group, use the inituser
or initgroup elements respectively. Both elements can be provided
either a user (resp. group) id or a name. Prefixing the user or group id with
a + will force it to be considered like a numeric value. Without
this, it will be first tried as a user or group name.
<os>
<type arch='x86_64'>exe</type>
<init>/bin/systemd</init>
<initarg>--unit</initarg>
<initarg>emergency.service</initarg>
<initenv name='MYENV'>some value</initenv>
<initdir>/my/custom/cwd</initdir>
<inituser>tester</inituser>
<initgroup>1000</initgroup>
</os>
If you want to enable user namespace, set the idmap element.
The uid and gid elements have three attributes:
starttargetcount
<idmap>
<uid start='0' target='1000' count='10'/>
<gid start='0' target='1000' count='10'/>
</idmap>
Some hypervisors allow control over what system information is
presented to the guest (for example, SMBIOS fields can be
populated by a hypervisor and inspected via
the dmidecode command in the guest). The
optional sysinfo element covers all such categories
of information. Since 0.8.7
...
<os>
<smbios mode='sysinfo'/>
...
</os>
<sysinfo type='smbios'>
<bios>
<entry name='vendor'>LENOVO</entry>
</bios>
<system>
<entry name='manufacturer'>Fedora</entry>
<entry name='product'>Virt-Manager</entry>
<entry name='version'>0.9.4</entry>
</system>
<baseBoard>
<entry name='manufacturer'>LENOVO</entry>
<entry name='product'>20BE0061MC</entry>
<entry name='version'>0B98401 Pro</entry>
<entry name='serial'>W1KS427111E</entry>
</baseBoard>
<chassis>
<entry name='manufacturer'>Dell Inc.</entry>
<entry name='version'>2.12</entry>
<entry name='serial'>65X0XF2</entry>
<entry name='asset'>40000101</entry>
<entry name='sku'>Type3Sku1</entry>
</chassis>
<oemStrings>
<entry>myappname:some arbitrary data</entry>
<entry>otherappname:more arbitrary data</entry>
</oemStrings>
</sysinfo>
...
The sysinfo element has a mandatory
attribute type that determine the layout of
sub-elements, with supported values of:
smbiossmbios sub-element of
the os element. Each
sub-element of sysinfo names a SMBIOS block, and
within those elements can be a list of entry
elements that describe a field within the block. The following
blocks and entries are recognized:
biosvendorversiondatereleasesystemmanufacturerproductversionserialuuiduuid element,
then the two values must match.skufamilybaseBoardmanufacturerproductversionserialassetlocationbios, system or baseBoard
blocks will be ignored without error. Other than uuid
validation and date format checking, all values are
passed as strings to the hypervisor driver.
chassismanufacturerversionserialassetskuoemStringsentry child elements, each providing
arbitrary string data. There are no restrictions on what data can
be provided in the entries, however, if the data is intended to be
consumed by an application in the guest, it is recommended to use
the application name as a prefix in the string. (Since 4.1.0)
<domain>
...
<vcpu placement='static' cpuset="1-4,^3,6" current="1">2</vcpu>
<vcpus>
<vcpu id='0' enabled='yes' hotpluggable='no' order='1'/>
<vcpu id='1' enabled='no' hotpluggable='yes'/>
</vcpus>
...
</domain>
vcpucpusetcpuset is a comma-separated
list of physical CPU numbers that domain process and virtual CPUs
can be pinned to by default. (NB: The pinning policy of domain
process and virtual CPUs can be specified separately by
cputune. If the attribute emulatorpin
of cputune is specified, the cpuset
specified by vcpu here will be ignored. Similarly,
for virtual CPUs which have the vcpupin specified,
the cpuset specified by cpuset here
will be ignored. For virtual CPUs which don't have
vcpupin specified, each will be pinned to the physical
CPUs specified by cpuset here).
Each element in that list is either a single CPU number,
a range of CPU numbers, or a caret followed by a CPU number to
be excluded from a previous range.
Since 0.4.4
currentcurrent can
be used to specify whether fewer than the maximum number of
virtual CPUs should be enabled.
Since 0.8.5
placementplacement can be used to
indicate the CPU placement mode for domain process. The value can
be either "static" or "auto", but defaults to placement
of numatune or "static" if cpuset is
specified. Using "auto" indicates the domain process will be pinned
to the advisory nodeset from querying numad and the value of
attribute cpuset will be ignored if it's specified.
If both cpuset and placement are not
specified or if placement is "static", but no
cpuset is specified, the domain process will be
pinned to all the available physical CPUs.
Since 0.9.11 (QEMU and KVM only)
vcpusid attribute specifies the vCPU id as used by libvirt
in other places such as vCPU pinning, scheduler information and NUMA
assignment. Note that the vCPU ID as seen in the guest may differ from
libvirt ID in certain cases. Valid IDs are from 0 to the maximum vCPU
count as set by the vcpu element minus 1.
The enabled attribute allows to control the state of the
vCPU. Valid values are yes and no.
hotpluggable controls whether given vCPU can be hotplugged
and hotunplugged in cases when the CPU is enabled at boot. Note that
all disabled vCPUs must be hotpluggable. Valid values are
yes and no.
order allows to specify the order to add the online vCPUs.
For hypervisors/platforms that require to insert multiple vCPUs at once
the order may be duplicated across all vCPUs that need to be
enabled at once. Specifying order is not necessary, vCPUs are then
added in an arbitrary order. If order info is used, it must be used for
all online vCPUs. Hypervisors may clear or update ordering information
during certain operations to assure valid configuration.
Note that hypervisors may create hotpluggable vCPUs differently from
boot vCPUs thus special initialization may be necessary.
Hypervisors may require that vCPUs enabled on boot which are not
hotpluggable are clustered at the beginning starting with ID 0. It may
be also required that vCPU 0 is always present and non-hotpluggable.
Note that providing state for individual CPUs may be necessary to enable
support of addressable vCPU hotplug and this feature may not be
supported by all hypervisors.
For QEMU the following conditions are required. vCPU 0 needs to be
enabled and non-hotpluggable. On PPC64 along with it vCPUs that are in
the same core need to be enabled as well. All non-hotpluggable CPUs
present at boot need to be grouped after vCPU 0.
Since 2.2.0 (QEMU only)
IOThreads are dedicated event loop threads for supported disk devices to perform block I/O requests in order to improve scalability especially on an SMP host/guest with many LUNs. Since 1.2.8 (QEMU only)
<domain> ... <iothreads>4</iothreads> ... </domain>
<domain>
...
<iothreadids>
<iothread id="2"/>
<iothread id="4"/>
<iothread id="6"/>
<iothread id="8"/>
</iothreadids>
...
</domain>
iothreadsiothreadidsiothreadids element provides the capability
to specifically define the IOThread ID's for the domain. By default,
IOThread ID's are sequentially numbered starting from 1 through the
number of iothreads defined for the domain. The
id attribute is used to define the IOThread ID. The
id attribute must be a positive integer greater than 0.
If there are less iothreadids defined than
iothreads defined for the domain, then libvirt will
sequentially fill iothreadids starting at 1 avoiding
any predefined id. If there are more
iothreadids defined than iothreads
defined for the domain, then the iothreads value
will be adjusted accordingly.
Since 1.2.15
<domain>
...
<cputune>
<vcpupin vcpu="0" cpuset="1-4,^2"/>
<vcpupin vcpu="1" cpuset="0,1"/>
<vcpupin vcpu="2" cpuset="2,3"/>
<vcpupin vcpu="3" cpuset="0,4"/>
<emulatorpin cpuset="1-3"/>
<iothreadpin iothread="1" cpuset="5,6"/>
<iothreadpin iothread="2" cpuset="7,8"/>
<shares>2048</shares>
<period>1000000</period>
<quota>-1</quota>
<global_period>1000000</global_period>
<global_quota>-1</global_quota>
<emulator_period>1000000</emulator_period>
<emulator_quota>-1</emulator_quota>
<iothread_period>1000000</iothread_period>
<iothread_quota>-1</iothread_quota>
<vcpusched vcpus='0-4,^3' scheduler='fifo' priority='1'/>
<iothreadsched iothreads='2' scheduler='batch'/>
<cachetune vcpus='0-3'>
<cache id='0' level='3' type='both' size='3' unit='MiB'/>
<cache id='1' level='3' type='both' size='3' unit='MiB'/>
<monitor level='3' vcpus='1'/>
<monitor level='3' vcpus='0-3'/>
</cachetune>
<cachetune vcpus='4-5'>
<monitor level='3' vcpus='4'/>
<monitor level='3' vcpus='5'/>
</cachetune>
<memorytune vcpus='0-3'>
<node id='0' bandwidth='60'/>
</memorytune>
</cputune>
...
</domain>
cputunecputune element provides details
regarding the CPU tunable parameters for the domain.
Since 0.9.0
vcpupinvcpupin element specifies which of host's
physical CPUs the domain vCPU will be pinned to. If this is omitted,
and attribute cpuset of element vcpu is
not specified, the vCPU is pinned to all the physical CPUs by default.
It contains two required attributes, the attribute vcpu
specifies vCPU id, and the attribute cpuset is same as
attribute cpuset of element vcpu.
(NB: Only qemu driver support)
Since 0.9.0
emulatorpinemulatorpin element specifies which of host
physical CPUs the "emulator", a subset of a domain not including vCPU
or iothreads will be pinned to. If this is omitted, and attribute
cpuset of element vcpu is not specified,
"emulator" is pinned to all the physical CPUs by default. It contains
one required attribute cpuset specifying which physical
CPUs to pin to.
iothreadpiniothreadpin element specifies which of host
physical CPUs the IOThreads will be pinned to. If this is omitted
and attribute cpuset of element vcpu is
not specified, the IOThreads are pinned to all the physical CPUs
by default. There are two required attributes, the attribute
iothread specifies the IOThread ID and the attribute
cpuset specifying which physical CPUs to pin to. See
the iothreadids
description
for valid iothread values.
Since 1.2.9
sharesshares element specifies the proportional
weighted share for the domain. If this is omitted, it defaults to
the OS provided defaults. NB, There is no unit for the value,
it's a relative measure based on the setting of other VM,
e.g. A VM configured with value
2048 will get twice as much CPU time as a VM configured with value 1024.
Since 0.9.0
periodperiod element specifies the enforcement
interval (unit: microseconds). Within period, each vCPU of
the domain will not be allowed to consume more than quota
worth of runtime. The value should be in range [1000, 1000000]. A period
with value 0 means no value.
Only QEMU driver support since 0.9.4, LXC since
0.9.10
quotaquota element specifies the maximum allowed
bandwidth (unit: microseconds). A domain with quota as any
negative value indicates that the domain has infinite bandwidth for
vCPU threads, which means that it is not bandwidth controlled. The value
should be in range [1000, 18446744073709551] or less than 0. A quota
with value 0 means no value. You can use this feature to ensure that all
vCPUs run at the same speed.
Only QEMU driver support since 0.9.4, LXC since
0.9.10
global_periodglobal_period element specifies the
enforcement CFS scheduler interval (unit: microseconds) for the whole
domain in contrast with period which enforces the interval
per vCPU. The value should be in range 1000, 1000000]. A
global_period with value 0 means no value.
Only QEMU driver support since 1.3.3
global_quotaglobal_quota element specifies the maximum
allowed bandwidth (unit: microseconds) within a period for the whole
domain. A domain with global_quota as any negative
value indicates that the domain has infinite bandwidth, which means that
it is not bandwidth controlled. The value should be in range
[1000, 18446744073709551] or less than 0. A global_quota
with value 0 means no value.
Only QEMU driver support since 1.3.3
emulator_periodemulator_period element specifies the enforcement
interval (unit: microseconds). Within emulator_period, emulator
threads (those excluding vCPUs) of the domain will not be allowed to consume
more than emulator_quota worth of runtime. The value should be
in range [1000, 1000000]. A period with value 0 means no value.
Only QEMU driver support since 0.10.0
emulator_quotaemulator_quota element specifies the maximum
allowed bandwidth (unit: microseconds) for domain's emulator threads (those
excluding vCPUs). A domain with emulator_quota as any negative
value indicates that the domain has infinite bandwidth for emulator threads
(those excluding vCPUs), which means that it is not bandwidth controlled.
The value should be in range [1000, 18446744073709551] or less than 0. A
quota with value 0 means no value.
Only QEMU driver support since 0.10.0
iothread_periodiothread_period element specifies the
enforcement interval (unit: microseconds) for IOThreads. Within
iothread_period, each IOThread of the domain will
not be allowed to consume more than iothread_quota
worth of runtime. The value should be in range [1000, 1000000].
An iothread_period with value 0 means no value.
Only QEMU driver support since 2.1.0
iothread_quotaiothread_quota element specifies the maximum
allowed bandwidth (unit: microseconds) for IOThreads. A domain with
iothread_quota as any negative value indicates that the
domain IOThreads have infinite bandwidth, which means that it is
not bandwidth controlled. The value should be in range
[1000, 18446744073709551] or less than 0. An iothread_quota
with value 0 means no value. You can use this feature to ensure that
all IOThreads run at the same speed.
Only QEMU driver support since 2.1.0
vcpusched, iothreadsched
and emulatorschedvcpusched, iothreadsched
and emulatorsched elements specify the scheduler type
(values batch, idle, fifo,
rr) for particular vCPU, IOThread and emulator threads
respecively. For vcpusched and iothreadsched
the attributes vcpus and iothreads select
which vCPUs/IOThreads this setting applies to, leaving them out sets the
default. The element emulatorsched does not have that
attribute. Valid vcpus values start at 0 through one less
than the number of vCPU's defined for the
domain. Valid iothreads values are described in
the iothreadids
description.
If no iothreadids are defined, then libvirt numbers
IOThreads from 1 to the number of iothreads available
for the domain. For real-time schedulers (fifo,
rr), priority must be specified as
well (and is ignored for non-real-time ones). The value range
for the priority depends on the host kernel (usually 1-99).
Since 1.2.13
emulatorsched since 5.3.0
cachetuneSince 4.1.0cachetune element can control allocations for CPU
caches using the resctrl on the host. Whether or not is this supported
can be gathered from capabilities where some limitations like minimum
size and required granularity are reported as well. The required
attribute vcpus specifies to which vCPUs this allocation
applies. A vCPU can only be member of one cachetune element
allocation. The vCPUs specified by cachetune can be identical with those
in memorytune, however they are not allowed to overlap.
Supported subelements are:
cachelevelidtypecode for code
(instructions), data for data or both
for both code and data (unified). Currently the allocation can
be done only with the same type as the host supports, meaning
you cannot request both for host with CDP
(code/data prioritization) enabled.
sizeunit attribute can be used to scale
the value.
unit (optional)memory element
for Memory Allocation)
in which size is specified, defaults to bytes.
monitorSince 4.10.0monitor creates the cache
monitor(s) for current cache allocation and has the following
required attributes:
levelvcpusmemorytuneSince 4.7.0memorytune element can control allocations for
memory bandwidth using the resctrl on the host. Whether or not is this
supported can be gathered from capabilities where some limitations like
minimum bandwidth and required granularity are reported as well. The
required attribute vcpus specifies to which vCPUs this
allocation applies. A vCPU can only be member of one
memorytune element allocation. The vcpus specified
by memorytune can be identical to those specified by
cachetune. However they are not allowed to overlap each other.
Supported subelements are:
nodeidbandwidth<domain> ... <maxMemory slots='16' unit='KiB'>1524288</maxMemory> <memory unit='KiB'>524288</memory> <currentMemory unit='KiB'>524288</currentMemory> ... </domain>
memoryunit, which defaults to "KiB"
(kibibytes, 210 or blocks of 1024 bytes). Valid
units are "b" or "bytes" for bytes, "KB" for kilobytes
(103 or 1,000 bytes), "k" or "KiB" for kibibytes
(1024 bytes), "MB" for megabytes (106 or 1,000,000
bytes), "M" or "MiB" for mebibytes (220 or
1,048,576 bytes), "GB" for gigabytes (109 or
1,000,000,000 bytes), "G" or "GiB" for gibibytes
(230 or 1,073,741,824 bytes), "TB" for terabytes
(1012 or 1,000,000,000,000 bytes), or "T" or "TiB"
for tebibytes (240 or 1,099,511,627,776 bytes).
However, the value will be rounded up to the nearest kibibyte
by libvirt, and may be further rounded to the granularity
supported by the hypervisor. Some hypervisors also enforce a
minimum, such as 4000KiB.
In case NUMA is configured for the guest the
memory element can be omitted.
In the case of crash, optional attribute dumpCore
can be used to control whether the guest memory should be
included in the generated coredump or not (values "on", "off").
unit since 0.9.11,
dumpCore since 0.10.2
(QEMU only)maxMemory<memory> element or
the NUMA cell size configuration can be increased by hot-plugging of
memory to the limit specified by this element.
The unit attribute behaves the same as for
<memory>.
The slots attribute specifies the number of slots
available for adding memory to the guest. The bounds are hypervisor
specific.
Note that due to alignment of the memory chunks added via memory
hotplug the full size allocation specified by this element may be
impossible to achieve.
Since 1.2.14 supported by the QEMU driver.
currentMemorymemory element.
The unit attribute behaves the same as
for memory.
<domain>
...
<memoryBacking>
<hugepages>
<page size="1" unit="G" nodeset="0-3,5"/>
<page size="2" unit="M" nodeset="4"/>
</hugepages>
<nosharepages/>
<locked/>
<source type="file|anonymous|memfd"/>
<access mode="shared|private"/>
<allocation mode="immediate|ondemand"/>
<discard/>
</memoryBacking>
...
</domain>
The optional memoryBacking element may contain several
elements that influence how virtual memory pages are backed by host
pages.
hugepagespage element is
introduced. It has one compulsory attribute size which
specifies which hugepages should be used (especially useful on systems
supporting hugepages of different sizes). The default unit for the
size attribute is kilobytes (multiplier of 1024). If you
want to use different unit, use optional unit attribute.
For systems with NUMA, the optional nodeset attribute may
come handy as it ties given guest's NUMA nodes to certain hugepage
sizes. From the example snippet, one gigabyte hugepages are used for
every NUMA node except node number four. For the correct syntax see
this.nosharepageslockedhard_limit (see
memory tuning) on memory allocation
suitable for the specific environment at the same time to mitigate
the risks described above. Since 1.0.6sourcetype attribute, it's possible to
provide "file" to utilize file memorybacking or keep the
default "anonymous". Since 4.10.0,
you may choose "memfd" backing. (QEMU/KVM only)accessmode attribute, specify if the memory is
to be "shared" or "private". This can be overridden per numa node by
memAccess.allocationmode attribute, specify when to allocate
the memory by supplying either "immediate" or "ondemand".discard
<domain>
...
<memtune>
<hard_limit unit='G'>1</hard_limit>
<soft_limit unit='M'>128</soft_limit>
<swap_hard_limit unit='G'>2</swap_hard_limit>
<min_guarantee unit='bytes'>67108864</min_guarantee>
</memtune>
...
</domain>
memtunememtune element provides details
regarding the memory tunable parameters for the domain. If this is
omitted, it defaults to the OS provided defaults. For QEMU/KVM, the
parameters are applied to the QEMU process as a whole. Thus, when
counting them, one needs to add up guest RAM, guest video RAM, and
some memory overhead of QEMU itself. The last piece is hard to
determine so one needs guess and try. For each tunable, it
is possible to designate which unit the number is in on
input, using the same values as
for <memory>. For backwards
compatibility, output is always in
KiB. unit
since 0.9.11
Possible values for all *_limit parameters are in range from 0 to
VIR_DOMAIN_MEMORY_PARAM_UNLIMITED.hard_limithard_limit element is the maximum memory
the guest can use. The units for this value are kibibytes (i.e. blocks
of 1024 bytes). Users of QEMU and KVM are strongly advised not to set
this limit as domain may get killed by the kernel if the guess is too
low, and determining the memory needed for a process to run is an
undecidable problem; that said, if you already set
locked in
memory backing because your
workload demands it, you'll have to take into account the specifics of
your deployment and figure out a value for hard_limit that
is large enough to support the memory requirements of your guest, but
small enough to protect your host against a malicious guest locking all
memory.soft_limitsoft_limit element is the memory limit to
enforce during memory contention. The units for this value are
kibibytes (i.e. blocks of 1024 bytes)swap_hard_limitswap_hard_limit element is the maximum
memory plus swap the guest can use. The units for this value are
kibibytes (i.e. blocks of 1024 bytes). This has to be more than
hard_limit value providedmin_guaranteemin_guarantee element is the guaranteed
minimum memory allocation for the guest. The units for this value are
kibibytes (i.e. blocks of 1024 bytes). This element is only supported
by VMware ESX and OpenVZ drivers.
<domain>
...
<numatune>
<memory mode="strict" nodeset="1-4,^3"/>
<memnode cellid="0" mode="strict" nodeset="1"/>
<memnode cellid="2" mode="preferred" nodeset="2"/>
</numatune>
...
</domain>
numatunenumatune element provides details of
how to tune the performance of a NUMA host via controlling NUMA policy
for domain process. NB, only supported by QEMU driver.
Since 0.9.3
memorymemory element specifies how to allocate memory
for the domain process on a NUMA host. It contains several optional
attributes. Attribute mode is either 'interleave',
'strict', or 'preferred', defaults to 'strict'. Attribute
nodeset specifies the NUMA nodes, using the same syntax as
attribute cpuset of element vcpu. Attribute
placement (since 0.9.12) can be
used to indicate the memory placement mode for domain process, its value
can be either "static" or "auto", defaults to placement of
vcpu, or "static" if nodeset is specified.
"auto" indicates the domain process will only allocate memory from the
advisory nodeset returned from querying numad, and the value of attribute
nodeset will be ignored if it's specified.
If placement of vcpu is 'auto', and
numatune is not specified, a default numatune
with placement 'auto' and mode 'strict' will
be added implicitly.
Since 0.9.3
memnodememnode elements can specify memory allocation
policies per each guest NUMA node. For those nodes having no
corresponding memnode element, the default from
element memory will be used. Attribute cellid
addresses guest NUMA node for which the settings are applied.
Attributes mode and nodeset have the same
meaning and syntax as in memory element.
This setting is not compatible with automatic placement.
QEMU Since 1.2.7
<domain>
...
<blkiotune>
<weight>800</weight>
<device>
<path>/dev/sda</path>
<weight>1000</weight>
</device>
<device>
<path>/dev/sdb</path>
<weight>500</weight>
<read_bytes_sec>10000</read_bytes_sec>
<write_bytes_sec>10000</write_bytes_sec>
<read_iops_sec>20000</read_iops_sec>
<write_iops_sec>20000</write_iops_sec>
</device>
</blkiotune>
...
</domain>
blkiotuneblkiotune element provides the ability
to tune Blkio cgroup tunable parameters for the domain. If this is
omitted, it defaults to the OS provided
defaults. Since 0.8.8weightweight element is the overall I/O
weight of the guest. The value should be in the range [100,
1000]. After kernel 2.6.39, the value could be in the
range [10, 1000].devicedevice elements
that further tune the weights for each host block device in
use by the domain. Note that
multiple guest disks can share a
single host block device, if they are backed by files within
the same host file system, which is why this tuning parameter
is at the global domain level rather than associated with each
guest disk device (contrast this to
the <iotune>
element which can apply to an
individual <disk>).
Each device element has two
mandatory sub-elements, path describing the
absolute path of the device, and weight giving
the relative weight of that device, in the range [100,
1000]. After kernel 2.6.39, the value could be in the
range [10, 1000]. Since 0.9.8read_bytes_secwrite_bytes_secread_iops_secwrite_iops_sec
Hypervisors may allow for virtual machines to be placed into
resource partitions, potentially with nesting of said partitions.
The resource element groups together configuration
related to resource partitioning. It currently supports a child
element partition whose content defines the absolute path
of the resource partition in which to place the domain. If no
partition is listed, then the domain will be placed in a default
partition. It is the responsibility of the app/admin to ensure
that the partition exists prior to starting the guest. Only the
(hypervisor specific) default partition can be assumed to exist
by default.
... <resource> <partition>/virtualmachines/production</partition> </resource> ...
Resource partitions are currently supported by the QEMU and LXC drivers, which map partition paths to cgroups directories, in all mounted controllers. Since 1.0.5
Requirements for CPU model, its features and topology can be specified using the following collection of elements. Since 0.7.5
... <cpu match='exact'> <model fallback='allow'>core2duo</model> <vendor>Intel</vendor> <topology sockets='1' dies='1' cores='2' threads='1'/> <cache level='3' mode='emulate'/> <feature policy='disable' name='lahf_lm'/> </cpu> ...
<cpu mode='host-model'> <model fallback='forbid'/> <topology sockets='1' dies='1' cores='2' threads='1'/> </cpu> ...
<cpu mode='host-passthrough'> <cache mode='passthrough'/> <feature policy='disable' name='lahf_lm'/> ...
In case no restrictions need to be put on CPU model and its features, a
simpler cpu element can be used.
Since 0.7.6
... <cpu> <topology sockets='1' dies='1' cores='2' threads='1'/> </cpu> ...
cpucpu element is the main container for describing
guest CPU requirements. Its match attribute specifies how
strictly the virtual CPU provided to the guest matches these
requirements. Since 0.7.6 the
match attribute can be omitted if topology
is the only element within cpu. Possible values for the
match attribute are:
minimumhost-model mode; the domain
will not be created if the provided virtual CPU does not meet
the requirements.exactstrictmatch
attribute can be omitted and will default to exact.
Sometimes the hypervisor is not able to create a virtual CPU exactly
matching the specification passed by libvirt.
Since 3.2.0, an optional check
attribute can be used to request a specific way of checking whether
the virtual CPU matches the specification. It is usually safe to omit
this attribute when starting a domain and stick with the default
value. Once the domain starts, libvirt will automatically change the
check attribute to the best supported value to ensure the
virtual CPU does not change when the domain is migrated to another
host. The following values can be used:
nonepartialfullmode
attribute may be used to make it easier to configure a guest CPU to be
as close to host CPU as possible. Possible values for the
mode attribute are:
customcpu element describes the CPU
that should be presented to the guest. This is the default when no
mode attribute is specified. This mode makes it so that
a persistent guest will see the same hardware no matter what host
the guest is booted on.host-modelhost-model mode is essentially a shortcut to
copying host CPU definition from capabilities XML into domain XML.
Since the CPU definition is copied just before starting a domain,
exactly the same XML can be used on different hosts while still
providing the best guest CPU each host supports. The
match attribute can't be used in this mode. Specifying
CPU model is not supported either, but model's
fallback attribute may still be used. Using the
feature element, specific flags may be enabled or
disabled specifically in addition to the host model. This may be
used to fine tune features that can be emulated.
(Since 1.1.1).
Libvirt does not model every aspect of each CPU so
the guest CPU will not match the host CPU exactly. On the other
hand, the ABI provided to the guest is reproducible. During
migration, complete CPU model definition is transferred to the
destination host so the migrated guest will see exactly the same CPU
model for the running instance of the guest, even if the destination
host contains more capable CPUs or newer kernel; but shutting down and restarting
the guest may present different hardware to the guest according to
the capabilities of the new host. Prior to libvirt 3.2.0 and QEMU
2.9.0 detection of the host CPU model via QEMU is not supported.
Thus the CPU configuration created using host-model
may not work as expected.
Since 3.2.0 and QEMU 2.9.0 this mode
works the way it was designed and it is indicated by the
fallback attribute set to forbid in the
host-model CPU definition advertised in
domain capabilities XML.
When fallback attribute is set to allow
in the domain capabilities XML, it is recommended to use
custom mode with just the CPU model from the host
capabilities XML. Since 1.2.11 PowerISA
allows processors to run VMs in binary compatibility mode supporting
an older version of ISA. Libvirt on PowerPC architecture uses the
host-model to signify a guest mode CPU running in
binary compatibility mode. Example:
When a user needs a power7 VM to run in compatibility mode
on a Power8 host, this can be described in XML as follows :
<cpu mode='host-model'> <model>power7</model> </cpu> ...
host-passthroughfeature elements. Migration of a guest
using host-passthrough is dangerous if the source and destination hosts
are not identical in both hardware, QEMU version, microcode version
and configuration. If such a migration is attempted then the guest may
hang or crash upon resuming execution on the destination host.host-model and host-passthrough modes
make sense when a domain can run directly on the host CPUs (for
example, domains with type kvm). The actual host CPU is
irrelevant for domains with emulated virtual CPUs (such as domains with
type qemu). However, for backward compatibility
host-model may be implemented even for domains running on
emulated CPUs in which case the best CPU the hypervisor is able to
emulate may be used rather then trying to mimic the host CPU model.
modelmodel element specifies CPU model
requested by the guest. The list of available CPU models and their
definition can be found in cpu_map.xml file installed
in libvirt's data directory. If a hypervisor is not able to use the
exact CPU model, libvirt automatically falls back to a closest model
supported by the hypervisor while maintaining the list of CPU
features. Since 0.9.10, an optional
fallback attribute can be used to forbid this behavior,
in which case an attempt to start a domain requesting an unsupported
CPU model will fail. Supported values for fallback
attribute are: allow (this is the default), and
forbid. The optional vendor_id attribute
(Since 0.10.0) can be used to set the
vendor id seen by the guest. It must be exactly 12 characters long.
If not set the vendor id of the host is used. Typical possible
values are "AuthenticAMD" and "GenuineIntel".vendorvendor element specifies CPU vendor requested by the
guest. If this element is missing, the guest can be run on a CPU
matching given features regardless on its vendor. The list of
supported vendors can be found in cpu_map.xml.topologytopology element specifies requested topology of
virtual CPU provided to the guest. Four attributes, sockets,
dies, cores, and threads,
accept non-zero positive integer values. They refer to the number of
CPU sockets per NUMA node, number of dies per socket, number of cores
per die, and number of threads per core, respectively. The dies
attribute is optional and will default to 1 if omitted, while the other
attributes are all mandatory. Hypervisors may require that the maximum
number of vCPUs specified by the cpus element equals to
the number of vcpus resulting from the topology.featurecpu element can contain zero or more
elements used to fine-tune features provided by the
selected CPU model. The list of known feature names can be found in
the same file as CPU models. The meaning of each feature
element depends on its policy attribute, which has to be
set to one of the following values:
forcerequireoptionaldisableforbidpolicy
attribute can be omitted and will default to require.
Individual CPU feature names are specified as part of the
name attribute. For example, to explicitly specify
the 'pcid' feature with Intel IvyBridge CPU model:
... <cpu match='exact'> <model fallback='forbid'>IvyBridge</model> <vendor>Intel</vendor> <feature policy='require' name='pcid'/> </cpu> ...
cachecache
element describes the virtual CPU cache. If the element is missing,
the hypervisor will use a sensible default.
levelcache elements with
the level attribute set and those without the
attribute is forbidden.modeemulatepassthroughdisablelevel attribute
is missing).
Guest NUMA topology can be specified using the numa element.
Since 0.9.8
...
<cpu>
...
<numa>
<cell id='0' cpus='0-3' memory='512000' unit='KiB' discard='yes'/>
<cell id='1' cpus='4-7' memory='512000' unit='KiB' memAccess='shared'/>
</numa>
...
</cpu>
...
Each cell element specifies a NUMA cell or a NUMA node.
cpus specifies the CPU or range of CPUs that are
part of the node. memory specifies the node memory
in kibibytes (i.e. blocks of 1024 bytes).
Since 1.2.11 one can use an additional unit attribute to
define units in which memory is specified.
Since 1.2.7 all cells should
have id attribute in case referring to some cell is
necessary in the code, otherwise the cells are
assigned ids in the increasing order starting from
0. Mixing cells with and without the id attribute
is not recommended as it may result in unwanted behaviour.
Since 1.2.9 the optional attribute
memAccess can control whether the memory is to be
mapped as "shared" or "private". This is valid only for
hugepages-backed memory and nvdimm modules.
Each cell element can have an optional
discard attribute which fine tunes the discard
feature for given numa node as described under
Memory Backing.
Accepted values are yes and no.
Since 4.4.0
This guest NUMA specification is currently available only for QEMU/KVM and Xen.
A NUMA hardware architecture supports the notion of distances
between NUMA cells. Since 3.10.0 it
is possible to define the distance between NUMA cells using the
distances element within a NUMA cell
description. The sibling sub-element is used to
specify the distance value between sibling NUMA cells. For more
details, see the chapter explaining the system's SLIT (System
Locality Information Table) within the ACPI (Advanced
Configuration and Power Interface) specification.
...
<cpu>
...
<numa>
<cell id='0' cpus='0,4-7' memory='512000' unit='KiB'>
<distances>
<sibling id='0' value='10'/>
<sibling id='1' value='21'/>
<sibling id='2' value='31'/>
<sibling id='3' value='41'/>
</distances>
</cell>
<cell id='1' cpus='1,8-10,12-15' memory='512000' unit='KiB' memAccess='shared'>
<distances>
<sibling id='0' value='21'/>
<sibling id='1' value='10'/>
<sibling id='2' value='21'/>
<sibling id='3' value='31'/>
</distances>
</cell>
<cell id='2' cpus='2,11' memory='512000' unit='KiB' memAccess='shared'>
<distances>
<sibling id='0' value='31'/>
<sibling id='1' value='21'/>
<sibling id='2' value='10'/>
<sibling id='3' value='21'/>
</distances>
</cell>
<cell id='3' cpus='3' memory='512000' unit='KiB'>
<distances>
<sibling id='0' value='41'/>
<sibling id='1' value='31'/>
<sibling id='2' value='21'/>
<sibling id='3' value='10'/>
</distances>
</cell>
</numa>
...
</cpu>
...
Describing distances between NUMA cells is currently only supported
by Xen and QEMU. If no distances are given to describe
the SLIT data between different cells, it will default to a scheme
using 10 for local and 20 for remote distances.
It is sometimes necessary to override the default actions taken
on various events. Not all hypervisors support all events and actions.
The actions may be taken as a result of calls to libvirt APIs
virDomainReboot
,
virDomainShutdown
,
or
virDomainShutdownFlags
.
Using virsh reboot or virsh shutdown would
also trigger the event.
... <on_poweroff>destroy</on_poweroff> <on_reboot>restart</on_reboot> <on_crash>restart</on_crash> <on_lockfailure>poweroff</on_lockfailure> ...
The following collections of elements allow the actions to be specified when a guest OS triggers a lifecycle operation. A common use case is to force a reboot to be treated as a poweroff when doing the initial OS installation. This allows the VM to be re-configured for the first post-install bootup.
on_poweroffon_rebooton_crashEach of these states allow for the same four possible actions.
destroyrestartpreserverename-restart
QEMU/KVM supports the on_poweroff and on_reboot
events handling the destroy and restart actions.
The preserve action for an on_reboot event
is treated as a destroy and the rename-restart
action for an on_poweroff event is treated as a
restart event.
The on_crash event supports these additional
actions since 0.8.4.
coredump-destroycoredump-restart
Since 3.9.0, the lifecycle events can
be configured via the
virDomainSetLifecycleAction API.
The on_lockfailure element (since
1.0.0) may be used to configure what action should be
taken when a lock manager loses resource locks. The following
actions are recognized by libvirt, although not all of them need
to be supported by individual lock managers. When no action is
specified, each lock manager will take its default action.
poweroffrestartpauseignoreSince 0.10.2 it is possible to forcibly enable or disable BIOS advertisements to the guest OS. (NB: Only qemu driver support)
... <pm> <suspend-to-disk enabled='no'/> <suspend-to-mem enabled='yes'/> </pm> ...
pmHypervisors may allow certain CPU / machine features to be toggled on/off.
...
<features>
<pae/>
<acpi/>
<apic/>
<hap/>
<privnet/>
<hyperv>
<relaxed state='on'/>
<vapic state='on'/>
<spinlocks state='on' retries='4096'/>
<vpindex state='on'/>
<runtime state='on'/>
<synic state='on'/>
<stimer state='on'>
<direct state='on'/>
</stimer>
<reset state='on'/>
<vendor_id state='on' value='KVM Hv'/>
<frequencies state='on'/>
<reenlightenment state='on'/>
<tlbflush state='on'/>
<ipi state='on'/>
<evmcs state='on'/>
</hyperv>
<kvm>
<hidden state='on'/>
<hint-dedicated state='on'/>
</kvm>
<pvspinlock state='on'/>
<gic version='2'/>
<ioapic driver='qemu'/>
<hpt resizing='required'>
<maxpagesize unit='MiB'>16</maxpagesize>
</hpt>
<vmcoreinfo state='on'/>
<smm state='on'>
<tseg unit='MiB'>48</tseg>
</smm>
<htm state='on'/>
<ccf-assist state='on'/>
<msrs unknown='ignore'/>
</features>
...
All features are listed within the features
element, omitting a togglable feature tag turns it off.
The available features can be found by asking
for the capabilities XML and
domain capabilities XML,
but a common set for fully virtualized domains are:
paeacpiapiceoi with values on
and off which toggles the availability of EOI (End of
Interrupt) for the guest.
hapstate attribute (values on,
off) enable or disable use of Hardware Assisted Paging.
The default is on if the hypervisor detects availability
of Hardware Assisted Paging.
viridianprivnethyperv| Feature | Description | Value | Since |
|---|---|---|---|
| relaxed | Relax constraints on timers | on, off | 1.0.0 (QEMU 2.0) |
| vapic | Enable virtual APIC | on, off | 1.1.0 (QEMU 2.0) |
| spinlocks | Enable spinlock support | on, off; retries - at least 4095 | 1.1.0 (QEMU 2.0) |
| vpindex | Virtual processor index | on, off | 1.3.3 (QEMU 2.5) |
| runtime | Processor time spent on running guest code and on behalf of guest code | on, off | 1.3.3 (QEMU 2.5) |
| synic | Enable Synthetic Interrupt Controller (SynIC) | on, off | 1.3.3 (QEMU 2.6) |
| stimer | Enable SynIC timers, optionally with Direct Mode support | on, off; direct - on,off | 1.3.3 (QEMU 2.6), direct mode 5.7.0 (QEMU 4.1) |
| reset | Enable hypervisor reset | on, off | 1.3.3 (QEMU 2.5) |
| vendor_id | Set hypervisor vendor id | on, off; value - string, up to 12 characters | 1.3.3 (QEMU 2.5) |
| frequencies | Expose frequency MSRs | on, off | 4.7.0 (QEMU 2.12) |
| reenlightenment | Enable re-enlightenment notification on migration | on, off | 4.7.0 (QEMU 3.0) |
| tlbflush | Enable PV TLB flush support | on, off | 4.7.0 (QEMU 3.0) |
| ipi | Enable PV IPI support | on, off | 4.10.0 (QEMU 3.1) |
| evmcs | Enable Enlightened VMCS | on, off | 4.10.0 (QEMU 3.1) |
pvspinlockstate='off'
attribute.
kvm| Feature | Description | Value | Since |
|---|---|---|---|
| hidden | Hide the KVM hypervisor from standard MSR based discovery | on, off | 1.2.8 (QEMU 2.1.0) |
| hint-dedicated | Allows a guest to enable optimizations when running on dedicated vCPUs | on, off | 5.7.0 (QEMU 2.12.0) |
pmustate attribute (values on,
off, default on) enable or disable the
performance monitoring unit for the guest.
Since 1.2.12
vmportstate attribute (values on,
off, default on) enable or disable
the emulation of VMware IO port, for vmmouse etc.
Since 1.2.16
gicgic instead of apic. The optional
attribute version specifies the GIC version;
however, it may not be supported by all hypervisors. Accepted
values are 2, 3 and host.
Since 1.2.16
smm
Depending on the state attribute (values on,
off, default on) enable or disable
System Management Mode.
Since 2.1.0
Optional sub-element tseg can be used to specify
the amount of memory dedicated to SMM's extended TSEG. That offers a
fourth option size apart from the existing ones (1 MiB, 2 MiB and 8
MiB) that the guest OS (or rather loader) can choose from. The size
can be specified as a value of that element, optional attribute
unit can be used to specify the unit of the
aforementioned value (defaults to 'MiB'). If set to 0 the extended
size is not advertised and only the default ones (see above) are
available.
If the VM is booting you should leave this option alone, unless you are very certain you know what you are doing.
This value is configurable due to the fact that the calculation cannot
be done right with the guarantee that it will work correctly. In
QEMU, the user-configurable extended TSEG feature was unavailable up
to and including pc-q35-2.9. Starting with
pc-q35-2.10 the feature is available, with default size
16 MiB. That should suffice for up to roughly 272 vCPUs, 5 GiB guest
RAM in total, no hotplug memory range, and 32 GiB of 64-bit PCI MMIO
aperture. Or for 48 vCPUs, with 1TB of guest RAM, no hotplug DIMM
range, and 32GB of 64-bit PCI MMIO aperture. The values may also vary
based on the loader the VM is using.
Additional size might be needed for significantly higher vCPU counts or increased address space (that can be memory, maxMemory, 64-bit PCI MMIO aperture size; roughly 8 MiB of TSEG per 1 TiB of address space) which can also be rounded up.
Due to the nature of this setting being similar to "how much RAM should the guest have" users are advised to either consult the documentation of the guest OS or loader (if there is any), or test this by trial-and-error changing the value until the VM boots successfully. Yet another guiding value for users might be the fact that 48 MiB should be enough for pretty large guests (240 vCPUs and 4TB guest RAM), but it is on purpose not set as default as 48 MiB of unavailable RAM might be too much for small guests (e.g. with 512 MiB of RAM).
See Memory Allocation
for more details about the unit attribute.
Since 4.5.0 (QEMU only)
ioapicdriver attribute are:
kvm (default for KVM domains)
and qemu which puts I/O APIC in userspace
which is also known as a split I/O APIC mode.
Since 3.4.0 (QEMU/KVM only)
hptresizing attribute are
enabled, which causes HPT resizing to be enabled if
both the guest and the host support it; disabled, which
causes HPT resizing to be disabled regardless of guest and host
support; and required, which prevents the guest from
starting unless both the guest and the host support HPT resizing. If
the attribute is not defined, the hypervisor default will be used.
Since 3.10.0 (QEMU/KVM only).
The optional maxpagesize subelement can be used to
limit the usable page size for HPT guests. Common values are 64 KiB,
16 MiB and 16 GiB; when not specified, the hypervisor default will
be used. Since 4.5.0 (QEMU/KVM only).
vmcoreinfohtmstate attribute
are on and off. If the attribute is not
defined, the hypervisor default will be used.
Since 4.6.0 (QEMU/KVM only)
nested-hvstate attribute are
on and off. If the attribute is not
defined, the hypervisor default will be used.
Since 4.10.0 (QEMU/KVM only)
msrsunknown attribute
of msrs to ignore. If the attribute is
not defined, or set to fault, unknown reads and writes
will not be ignored.
Since 5.1.0 (bhyve only)
ccf-assiststate attribute
are on and off. If the attribute is not
defined, the hypervisor default will be used.
Since 5.9.0 (QEMU/KVM only)
The guest clock is typically initialized from the host clock. Most operating systems expect the hardware clock to be kept in UTC, and this is the default. Windows, however, expects it to be in so called 'localtime'.
...
<clock offset='localtime'>
<timer name='rtc' tickpolicy='catchup' track='guest'>
<catchup threshold='123' slew='120' limit='10000'/>
</timer>
<timer name='pit' tickpolicy='delay'/>
</clock>
...
clockThe offset attribute takes four possible
values, allowing fine grained control over how the guest
clock is synchronized to the host. NB, not all hypervisors
support all modes.
utcadjustment attribute. If the value is 'reset', the
conversion is never done (not all hypervisors can
synchronize to UTC on each boot; use of 'reset' will cause
an error on those hypervisors). A numeric value
forces the conversion to 'variable' mode using the value as the
initial adjustment. The default adjustment is
hypervisor specific.
localtimeadjustment
attribute behaves the same as in 'utc' mode.
timezonetimezone attribute.
Since 0.7.7
variablebasis
attribute. The delta relative to UTC (or localtime) is specified
in seconds, using the adjustment attribute.
The guest is free to adjust the RTC over time and expect
that it will be honored at next reboot. This is in
contrast to 'utc' and 'localtime' mode (with the optional
attribute adjustment='reset'), where the RTC adjustments are
lost at each reboot. Since 0.7.7
Since 0.9.11 the basis
attribute can be either 'utc' (default) or 'localtime'.
A clock may have zero or more
timer sub-elements. Since
0.8.0
timer
Each timer element requires a name attribute,
and has other optional attributes that depend on
the name specified. Various hypervisors
support different combinations of attributes.
namename attribute selects which timer is
being modified, and can be one of
"platform" (currently unsupported),
"hpet" (libxl, xen, qemu, lxc), "kvmclock" (qemu),
"pit" (qemu), "rtc" (qemu, lxc), "tsc" (libxl, qemu -
since 3.2.0), "hypervclock"
(qemu - since 1.2.2) or
"armvtimer" (qemu - since 6.1.0).
The hypervclock timer adds support for the
reference time counter and the reference page for iTSC
feature for guests running the Microsoft Windows
operating system.
tracktrack attribute specifies what the timer
tracks, and can be "boot", "guest", or "wall".
Only valid for name="rtc"
or name="platform".
tickpolicy
The tickpolicy attribute determines what
happens when QEMU misses a deadline for injecting a
tick to the guest. This can happen, for example, because the
guest was paused.
delaycatchupmergediscardIf the policy is "catchup", there can be further details in
the catchup sub-element.
catchupcatchup element has three optional
attributes, each a positive integer. The attributes
are threshold, slew,
and limit.
Note that hypervisors are not required to support all policies across all time sources
frequencyfrequency attribute is an unsigned
integer specifying the frequency at
which name="tsc" runs.
modemode attribute controls how
the name="tsc" timer is managed, and can be
"auto", "native", "emulate", "paravirt", or "smpsafe".
Other timers are always emulated.
presentpresent attribute can be "yes" or "no" to
specify whether a particular timer is available to the guest.
Some platforms allow monitoring of performance of the virtual machine and
the code executed inside. To enable the performance monitoring events
you can either specify them in the perf element or enable
them via virDomainSetPerfEvents API. The performance values
are then retrieved using the virConnectGetAllDomainStats API.
Since 2.0.0
... <perf> <event name='cmt' enabled='yes'/> <event name='mbmt' enabled='no'/> <event name='mbml' enabled='yes'/> <event name='cpu_cycles' enabled='no'/> <event name='instructions' enabled='yes'/> <event name='cache_references' enabled='no'/> <event name='cache_misses' enabled='no'/> <event name='branch_instructions' enabled='no'/> <event name='branch_misses' enabled='no'/> <event name='bus_cycles' enabled='no'/> <event name='stalled_cycles_frontend' enabled='no'/> <event name='stalled_cycles_backend' enabled='no'/> <event name='ref_cpu_cycles' enabled='no'/> <event name='cpu_clock' enabled='no'/> <event name='task_clock' enabled='no'/> <event name='page_faults' enabled='no'/> <event name='context_switches' enabled='no'/> <event name='cpu_migrations' enabled='no'/> <event name='page_faults_min' enabled='no'/> <event name='page_faults_maj' enabled='no'/> <event name='alignment_faults' enabled='no'/> <event name='emulation_faults' enabled='no'/> </perf> ...
| event name | Description | stats parameter name |
|---|---|---|
cmt |
usage of l3 cache in bytes by applications running on the platform | perf.cmt |
mbmt |
total system bandwidth from one level of cache | perf.mbmt |
mbml |
bandwidth of memory traffic for a memory controller | perf.mbml |
cpu_cycles |
the count of CPU cycles (total/elapsed) | perf.cpu_cycles |
instructions |
the count of instructions by applications running on the platform | perf.instructions |
cache_references |
the count of cache hits by applications running on the platform | perf.cache_references |
cache_misses |
the count of cache misses by applications running on the platform | perf.cache_misses |
branch_instructions |
the count of branch instructions by applications running on the platform | perf.branch_instructions |
branch_misses |
the count of branch misses by applications running on the platform | perf.branch_misses |
bus_cycles |
the count of bus cycles by applications running on the platform | perf.bus_cycles |
stalled_cycles_frontend |
the count of stalled CPU cycles in the frontend of the instruction processor pipeline by applications running on the platform | perf.stalled_cycles_frontend |
stalled_cycles_backend |
the count of stalled CPU cycles in the backend of the instruction processor pipeline by applications running on the platform | perf.stalled_cycles_backend |
ref_cpu_cycles |
the count of total CPU cycles not affected by CPU frequency scaling by applications running on the platform | perf.ref_cpu_cycles |
cpu_clock |
the count of CPU clock time, as measured by a monotonic high-resolution per-CPU timer, by applications running on the platform | perf.cpu_clock |
task_clock |
the count of task clock time, as measured by a monotonic high-resolution CPU timer, specific to the task that is run by applications running on the platform | perf.task_clock |
page_faults |
the count of page faults by applications running on the platform. This includes minor, major, invalid and other types of page faults | perf.page_faults |
context_switches |
the count of context switches by applications running on the platform | perf.context_switches |
cpu_migrations |
the count of CPU migrations, that is, where the process moved from one logical processor to another, by applications running on the platform | perf.cpu_migrations |
page_faults_min |
the count of minor page faults, that is, where the page was present in the page cache, and therefore the fault avoided loading it from storage, by applications running on the platform | perf.page_faults_min |
page_faults_maj |
the count of major page faults, that is, where the page was not present in the page cache, and therefore had to be fetched from storage, by applications running on the platform | perf.page_faults_maj |
alignment_faults |
the count of alignment faults, that is when the load or store is not aligned properly, by applications running on the platform | perf.alignment_faults |
emulation_faults |
the count of emulation faults, that is when the kernel traps on unimplemented instrucions and emulates them for user space, by applications running on the platform | perf.emulation_faults |
The final set of XML elements are all used to describe devices
provided to the guest domain. All devices occur as children
of the main devices element.
Since 0.1.3
... <devices> <emulator>/usr/lib/xen/bin/qemu-dm</emulator> </devices> ...
emulatoremulator element specify
the fully qualified path to the device model emulator binary.
The capabilities XML specifies
the recommended default emulator to use for each particular
domain type / architecture combination.
To help users identifying devices they care about, every
device can have direct child alias element
which then has name attribute where users can
store identifier for the device. The identifier has to have
"ua-" prefix and must be unique within the domain. Additionally, the
identifier must consist only of the following characters:
[a-zA-Z0-9_-].
Since 3.9.0
<devices>
<disk type='file'>
<alias name='ua-myDisk'/>
</disk>
<interface type='network' trustGuestRxFilters='yes'>
<alias name='ua-myNIC'/>
</interface>
...
</devices>
Any device that looks like a disk, be it a floppy, harddisk,
cdrom, or paravirtualized driver is specified via the disk
element.
...
<devices>
<disk type='file' snapshot='external'>
<driver name="tap" type="aio" cache="default"/>
<source file='/var/lib/xen/images/fv0' startupPolicy='optional'>
<seclabel relabel='no'/>
</source>
<target dev='hda' bus='ide'/>
<iotune>
<total_bytes_sec>10000000</total_bytes_sec>
<read_iops_sec>400000</read_iops_sec>
<write_iops_sec>100000</write_iops_sec>
</iotune>
<boot order='2'/>
<encryption type='...'>
...
</encryption>
<shareable/>
<serial>
...
</serial>
</disk>
...
<disk type='network'>
<driver name="qemu" type="raw" io="threads" ioeventfd="on" event_idx="off"/>
<source protocol="sheepdog" name="image_name">
<host name="hostname" port="7000"/>
</source>
<target dev="hdb" bus="ide"/>
<boot order='1'/>
<transient/>
<address type='drive' controller='0' bus='1' unit='0'/>
</disk>
<disk type='network'>
<driver name="qemu" type="raw"/>
<source protocol="rbd" name="image_name2">
<host name="hostname" port="7000"/>
<snapshot name="snapname"/>
<config file="/path/to/file"/>
<auth username='myuser'>
<secret type='ceph' usage='mypassid'/>
</auth>
</source>
<target dev="hdc" bus="ide"/>
</disk>
<disk type='block' device='cdrom'>
<driver name='qemu' type='raw'/>
<target dev='hdd' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="http" name="url_path" query="foo=bar&baz=flurb>
<host name="hostname" port="80"/>
<cookies>
<cookie name="test">somevalue</cookie>
</cookies>
<readahead size='65536'/>
<timeout seconds='6'/>
</source>
<target dev='hde' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="https" name="url_path">
<host name="hostname" port="443"/>
<ssl verify="no"/>
</source>
<target dev='hdf' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="ftp" name="url_path">
<host name="hostname" port="21"/>
</source>
<target dev='hdg' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="ftps" name="url_path">
<host name="hostname" port="990"/>
</source>
<target dev='hdh' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="tftp" name="url_path">
<host name="hostname" port="69"/>
</source>
<target dev='hdi' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='block' device='lun'>
<driver name='qemu' type='raw'/>
<source dev='/dev/sda'>
<slices>
<slice type='storage' offset='12345' size='123'/>
</slices>
<reservations managed='no'>
<source type='unix' path='/path/to/qemu-pr-helper' mode='client'/>
</reservations>
</source>
<target dev='sda' bus='scsi'/>
<address type='drive' controller='0' bus='0' target='3' unit='0'/>
</disk>
<disk type='block' device='disk'>
<driver name='qemu' type='raw'/>
<source dev='/dev/sda'/>
<geometry cyls='16383' heads='16' secs='63' trans='lba'/>
<blockio logical_block_size='512' physical_block_size='4096'/>
<target dev='hdj' bus='ide'/>
</disk>
<disk type='volume' device='disk'>
<driver name='qemu' type='raw'/>
<source pool='blk-pool0' volume='blk-pool0-vol0'/>
<target dev='hdk' bus='ide'/>
</disk>
<disk type='network' device='disk'>
<driver name='qemu' type='raw'/>
<source protocol='iscsi' name='iqn.2013-07.com.example:iscsi-nopool/2'>
<host name='example.com' port='3260'/>
<auth username='myuser'>
<secret type='iscsi' usage='libvirtiscsi'/>
</auth>
</source>
<target dev='vda' bus='virtio'/>
</disk>
<disk type='network' device='lun'>
<driver name='qemu' type='raw'/>
<source protocol='iscsi' name='iqn.2013-07.com.example:iscsi-nopool/1'>
<host name='example.com' port='3260'/>
<auth username='myuser'>
<secret type='iscsi' usage='libvirtiscsi'/>
</auth>
</source>
<target dev='sdb' bus='scsi'/>
</disk>
<disk type='network' device='lun'>
<driver name='qemu' type='raw'/>
<source protocol='iscsi' name='iqn.2013-07.com.example:iscsi-nopool/0'>
<host name='example.com' port='3260'/>
<initiator>
<iqn name='iqn.2013-07.com.example:client'/>
</initiator>
</source>
<target dev='sdb' bus='scsi'/>
</disk>
<disk type='volume' device='disk'>
<driver name='qemu' type='raw'/>
<source pool='iscsi-pool' volume='unit:0:0:1' mode='host'/>
<target dev='vdb' bus='virtio'/>
</disk>
<disk type='volume' device='disk'>
<driver name='qemu' type='raw'/>
<source pool='iscsi-pool' volume='unit:0:0:2' mode='direct'/>
<target dev='vdc' bus='virtio'/>
</disk>
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2' queues='4'/>
<source file='/var/lib/libvirt/images/domain.qcow'/>
<backingStore type='file'>
<format type='qcow2'/>
<source file='/var/lib/libvirt/images/snapshot.qcow'/>
<backingStore type='block'>
<format type='raw'/>
<source dev='/dev/mapper/base'/>
<backingStore/>
</backingStore>
</backingStore>
<target dev='vdd' bus='virtio'/>
</disk>
<disk type='nvme' device='disk'>
<driver name='qemu' type='raw'/>
<source type='pci' managed='yes' namespace='1'>
<address domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
</source>
<target dev='vde' bus='virtio'/>
</disk>
</devices>
...
diskdisk element is the main container for
describing disks and supports the following attributes:
typedevice
Using "lun" (since 0.9.10) is only
valid when the type is "block" or "network" for
protocol='iscsi' or when the type
is "volume" when using an iSCSI source pool
for mode "host" or as an
NPIV
virtual Host Bus Adapter (vHBA) using a Fibre Channel storage pool.
Configured in this manner, the LUN behaves identically to "disk",
except that generic SCSI commands from the guest are accepted
and passed through to the physical device. Also note that
device='lun' will only be recognized for actual raw devices,
but never for individual partitions or LVM partitions (in those
cases, the kernel will reject the generic SCSI commands, making
it identical to device='disk').
Since 0.1.4
modelbus property but
for bus "virtio" the model can be specified further
with "virtio-transitional", "virtio-non-transitional", or
"virtio". See
Virtio transitional devices
for more details.
Since 5.2.0
rawiorawio intends
to confine the capability per-device, however, current QEMU
implementation gives the domain process broader capability
than that (per-process basis, affects all the domain disks).
To confine the capability as much as possible for QEMU driver
as this stage, sgio is recommended, it's more
secure than rawio.
Since 0.9.10
sgiodevice is 'lun'.
Since 1.0.2
snapshotinternal" requires a file format such as qcow2 that
can store both the snapshot and the data changes since the snapshot;
"external" will separate the snapshot from the live
data; and "no" means the disk will not participate in
snapshots. Read-only disks default to "no", while the
default for other disks depends on the hypervisor's capabilities.
Some hypervisors allow a per-snapshot choice as well, during
domain snapshot creation.
Not all snapshot modes are supported; for example, enabling
snapshots with a transient disk generally does not make sense.
Since 0.9.5
sourcesource depends on the
disk type attribute value as follows:
filefile attribute specifies the fully-qualified
path to the file holding the disk.
Since 0.0.3
blockdev attribute specifies the fully-qualified path
to the host device to serve as the disk.
Since 0.0.3
dirdir attribute specifies the fully-qualified path
to the directory to use as the disk.
Since 0.7.5
networkprotocol attribute specifies the protocol to
access to the requested image. Possible values are "nbd",
"iscsi", "rbd", "sheepdog", "gluster", "vxhs", "http", "https",
"ftp", ftps", or "tftp".
For any protocol other than nbd
an additional attribute name
is mandatory to specify which volume/image will be used.
For "nbd", the name attribute is optional. TLS
transport for NBD can be enabled by setting the tls
attribute to yes. For the QEMU hypervisor, usage of
a TLS environment can also be globally controlled on the host by
the nbd_tls and nbd_tls_x509_cert_dir in
/etc/libvirt/qemu.conf.
('tls' Since 4.5.0)
For protocols http and https an
optional attribute query specifies the query string.
(Since 6.2.0)
For "iscsi" (since 1.0.4), the
name attribute may include a logical unit number,
separated from the target's name by a slash (e.g.,
iqn.2013-07.com.example:iscsi-pool/1). If not
specified, the default LUN is zero.
For "vxhs" (since 3.8.0), the
name is the UUID of the volume, assigned by the
HyperScale server. Additionally, an optional attribute
tls (QEMU only) can be used to control whether a
VxHS block device would utilize a hypervisor configured TLS
X.509 certificate environment in order to encrypt the data
channel. For the QEMU hypervisor, usage of a TLS environment can
also be globally controlled on the host by the
vxhs_tls and vxhs_tls_x509_cert_dir or
default_tls_x509_cert_dir settings in the file
/etc/libvirt/qemu.conf. If vxhs_tls is enabled,
then unless the domain tls attribute is set to "no",
libvirt will use the host configured TLS environment. If the
tls attribute is set to "yes", then regardless of
the qemu.conf setting, TLS authentication will be attempted.
volumepool and volume. Attribute
pool specifies the name of the
storage pool (managed
by libvirt) where the disk source resides. Attribute
volume specifies the name of storage volume (managed
by libvirt) used as the disk source. The value for the
volume attribute will be the output from the "Name"
column of a virsh vol-list [pool-name] command.
Use the attribute mode
(since 1.1.1) to indicate how to
represent the LUN as the disk source. Valid values are
"direct" and "host". If mode is not specified,
the default is to use "host".
Using "direct" as the mode value indicates to use
the storage pool's
source element host attribute as
the disk source to generate the libiscsi URI (e.g.
'file=iscsi://example.com:3260/iqn.2013-07.com.example:iscsi-pool/1').
Using "host" as the mode value indicates to use the
LUN's path as it shows up on host (e.g.
'file=/dev/disk/by-path/ip-example.com:3260-iscsi-iqn.2013-07.com.example:iscsi-pool-lun-1').
Using a LUN from an iSCSI source pool provides the same
features as a disk configured using
type 'block' or 'network' and device
of 'lun' with respect to how the LUN is presented to and
may be used by the guest.
Since 1.0.5
nvmesource
element has the following attributes:
typeaddress
sub-element. Currently, only pci value is
accepted.
managedyes)
or expect the controller to be detached by system
administrator (no).
namespace<disk type='nvme'>
and <hostdev/> is that the latter is plain
host device assignment with all its limitations (e.g. no live
migration), while the former makes hypervisor to run the NVMe
disk through hypervisor's block layer thus enabling all
features provided by the layer (e.g. snapshots, domain
migration, etc.). Moreover, since the NVMe disk is unbinded
from its PCI driver, the host kernel storage stack is not
involved (compared to passing say /dev/nvme0n1 via
<disk type='block'> and therefore lower
latencies can be achieved.
seclabel, described
below (and since 0.9.9), can be
used to override the domain security labeling policy for just
that source file. (NB, for "volume" type disk, seclabel
is only valid when the specified storage volume is of 'file' or
'block' type).
The source element may also have the index
attribute with same semantics the
index attribute of backingStore
The source element may contain the following sub elements:
host
When the disk type is "network", the source
may have zero or more host sub-elements used to
specify the hosts to connect.
The host element supports 4 attributes, viz. "name",
"port", "transport" and "socket", which specify the hostname,
the port number, transport type and path to socket, respectively.
The meaning of this element and the number of the elements depend
on the protocol attribute.
| Protocol | Meaning | Number of hosts | Default port |
|---|---|---|---|
| nbd | a server running nbd-server | only one | 10809 |
| iscsi | an iSCSI server | only one | 3260 |
| rbd | monitor servers of RBD | one or more | librados default |
| sheepdog | one of the sheepdog servers (default is localhost:7000) | zero or one | 7000 |
| gluster | a server running glusterd daemon | one or more (Since 2.1.0), just one prior to that | 24007 |
| vxhs | a server running Veritas HyperScale daemon | only one | 9999 |
gluster supports "tcp", "rdma", "unix" as valid values for the transport attribute. nbd supports "tcp" and "unix". Others only support "tcp". If nothing is specified, "tcp" is assumed. If the transport is "unix", the socket attribute specifies the path to an AF_UNIX socket.
snapshotname attribute of snapshot element can
optionally specify an internal snapshot name to be used as the
source for storage protocols.
Supported for 'rbd' since 1.2.11 (QEMU only).
configfile attribute for the config element
provides a fully qualified path to a configuration file to be
provided as a parameter to the client of a networked storage
protocol. Supported for 'rbd' since 1.2.11
(QEMU only).
authauth element is supported for a disk
type "network" that is using a source
element with the protocol attributes "rbd" or "iscsi".
If present, the auth element provides the
authentication credentials needed to access the source. It
includes a mandatory attribute username, which
identifies the username to use during authentication, as well
as a sub-element secret with mandatory
attribute type, to tie back to
a libvirt secret object that
holds the actual password or other credentials (the domain XML
intentionally does not expose the password, only the reference
to the object that does manage the password).
Known secret types are "ceph" for Ceph RBD network sources and
"iscsi" for CHAP authentication of iSCSI targets.
Both will require either a uuid attribute
with the UUID of the secret object or a usage
attribute matching the key that was specified in the
secret object.
encryptionencryption can be a sub-element of the
source element for encrypted storage sources.
If present, specifies how the storage source is encrypted
See the
Storage Encryption
page for more information.
Note that the 'qcow' format of encryption is broken and thus is no
longer supported for use with disk images.
(Since libvirt 4.5.0)
reservationsreservations can be a sub-element of the
source element for storage sources (QEMU driver only).
If present it enables persistent reservations for SCSI
based disks. The element has one mandatory attribute
managed with accepted values yes and
no. If managed is enabled libvirt prepares
and manages any resources needed. When the persistent reservations
are unmanaged, then the hypervisor acts as a client and the path to
the server socket must be provided in the child element
source, which currently accepts only the following
attributes:
type with one value unix,
path path to the socket, and
finally mode which accepts one value
client specifying the role of hypervisor.
It's recommended to allow libvirt manage the persistent
reservations.
initiatorinitiator element is supported for a disk
type "network" that is using a source
element with the protocol attribute "iscsi".
If present, the initiator element provides the
initiator IQN needed to access the source via mandatory
attribute name.
addressnvme this element
specifies the PCI address of the host NVMe
controller.
Since 6.0.0
slicesslices element using its slice
sub-elements allows configuring offset and size of either the
location of the image format (slice type='storage')
inside the storage source or the guest data inside the image format
container (future expansion).
The offset and size values are in bytes.
Since 6.1.0
sslhttps and ftps accessed storage it's
possible to tweak the SSL transport parameters with this element.
The verify attribute allows to turn on or off SSL
certificate validation. Supported values are yes and
no. Since 6.2.0
cookieshttp and https accessed storage it's
possible to pass one or more cookies. The cookie name and value
must conform to the HTTP specification.
Since 6.2.0
readaheadtimeout
For a "file" or "volume" disk type which represents a cdrom or floppy
(the device attribute), it is possible to define
policy what to do with the disk if the source file is not accessible.
(NB, startupPolicy is not valid for "volume" disk unless
the specified storage volume is of "file" type). This is done by the
startupPolicy attribute
(since 0.9.7),
accepting these values:
| mandatory | fail if missing for any reason (the default) |
| requisite | fail if missing on boot up, drop if missing on migrate/restore/revert |
| optional | drop if missing at any start attempt |
Since 1.1.2 the startupPolicy
is extended to support hard disks besides cdrom and floppy. On guest
cold bootup, if a certain disk is not accessible or its disk chain is
broken, with startupPolicy 'optional' the guest will drop this disk.
This feature doesn't support migration currently.
backingStoresource element.
Since 1.2.4.
If the hypervisor driver does not support the
backingStoreInput
(Since 5.10.0)
domain feature the backingStore is ignored on
input and only used for output to describe the detected
backing chains of running domains.
If backingStoreInput is supported
the backingStore is used as the backing image of
source or other backingStore overriding
any backing image information recorded in the image metadata.
An empty backingStore element means the sibling
source is self-contained and is not based on any backing store.
For the detected backing chain information to be accurate, the
backing format must be correctly specified in the metadata of
each file of the chain (files created by libvirt satisfy this
property, but using existing external files for snapshot or
block copy operations requires the end user to pre-create the
file correctly). The following attributes are
supported in backingStore:
typetype attribute represents the type of disk used
by the backing store, see disk type attribute above for more
details and possible values.
indexvirDomainBlockRebase API). For example,
vda[2] refers to the backing store with
index='2' of the disk with vda target.
backingStore supports the following sub-elements:
formatformat element contains type
attribute which specifies the internal format of the backing
store, such as raw or qcow2.
sourcesource
element in disk. It specifies which file, device,
or network location contains the data of the described backing
store.
backingStorebackingStore
element.
mirrorsource sub-element will eventually have the
same contents as the source, and with the file format in the
sub-element format (which might differ from the
format of the source). The details of the source
sub-element are determined by the type attribute
of the mirror, similar to what is done for the
overall disk device element. The job
attribute mentions which API started the operation ("copy" for
the virDomainBlockRebase API, or "active-commit"
for the virDomainBlockCommit
API), since 1.2.7. The
attribute ready, if present, tracks progress of
the job: yes if the disk is known to be ready to
pivot, or, since
1.2.7, abort or pivot if the
job is in the process of completing. If ready is
not present, the disk is probably still
copying. For now, this element only valid in output; it is
ignored on input. The source sub-element exists
for all two-phase jobs since 1.2.6.
Older libvirt supported only block copy to a
file, since 0.9.12; for
compatibility with older clients, such jobs include redundant
information in the attributes file
and format in the mirror element.
targettarget element controls the bus / device
under which the disk is exposed to the guest
OS. The dev attribute indicates the "logical"
device name. The actual device name specified is not
guaranteed to map to the device name in the guest OS. Treat it
as a device ordering hint. The optional bus
attribute specifies the type of disk device to emulate;
possible values are driver specific, with typical values being
"ide", "scsi", "virtio", "xen", "usb", "sata", or
"sd" "sd" since 1.1.2. If omitted, the bus
type is inferred from the style of the device name (e.g. a device named
'sda' will typically be exported using a SCSI bus). The optional
attribute tray indicates the tray status of the
removable disks (i.e. CDROM or Floppy disk), the value can be either
"open" or "closed", defaults to "closed". NB, the value of
tray could be updated while the domain is running.
The optional attribute removable sets the
removable flag for USB disks, and its value can be either "on"
or "off", defaulting to "off". Since
0.0.3; bus attribute since 0.4.3;
tray attribute since 0.9.11; "usb" attribute value since
after 0.4.4; "sata" attribute value since 0.9.7; "removable" attribute
value since 1.1.3
iotuneiotune element provides the
ability to provide additional per-device I/O tuning, with
values that can vary for each device (contrast this to
the <blkiotune>
element, which applies globally to the domain). Currently,
the only tuning available is Block I/O throttling for qemu.
This element has optional sub-elements; any sub-element not
specified or given with a value of 0 implies no
limit. Since 0.9.8
total_bytes_sectotal_bytes_sec element is the
total throughput limit in bytes per second. This cannot
appear with read_bytes_sec
or write_bytes_sec.read_bytes_secread_bytes_sec element is the
read throughput limit in bytes per second.write_bytes_secwrite_bytes_sec element is the
write throughput limit in bytes per second.total_iops_sectotal_iops_sec element is the
total I/O operations per second. This cannot
appear with read_iops_sec
or write_iops_sec.read_iops_secread_iops_sec element is the
read I/O operations per second.write_iops_secwrite_iops_sec element is the
write I/O operations per second.total_bytes_sec_maxtotal_bytes_sec_max element is the
maximum total throughput limit in bytes per second. This cannot
appear with read_bytes_sec_max
or write_bytes_sec_max.read_bytes_sec_maxread_bytes_sec_max element is the
maximum read throughput limit in bytes per second.write_bytes_sec_maxwrite_bytes_sec_max element is the
maximum write throughput limit in bytes per second.total_iops_sec_maxtotal_iops_sec_max element is the
maximum total I/O operations per second. This cannot
appear with read_iops_sec_max
or write_iops_sec_max.read_iops_sec_maxread_iops_sec_max element is the
maximum read I/O operations per second.write_iops_sec_maxwrite_iops_sec_max element is the
maximum write I/O operations per second.size_iops_secsize_iops_sec element is the
size of I/O operations per second.
Throughput limits since 1.2.11 and QEMU 1.7
group_namegroup_name provides the cability
to share I/O throttling quota between multiple drives. This
prevents end-users from circumventing a hosting provider's
throttling policy by splitting 1 large drive in N small drives
and getting N times the normal throttling quota. Any name may
be used.
group_name since 3.0.0 and QEMU 2.4
total_bytes_sec_max_lengthtotal_bytes_sec_max_length
element is the maximum duration in seconds for the
total_bytes_sec_max burst period. Only valid
when the total_bytes_sec_max is set.read_bytes_sec_max_lengthread_bytes_sec_max_length
element is the maximum duration in seconds for the
read_bytes_sec_max burst period. Only valid
when the read_bytes_sec_max is set.write_bytes_sec_maxwrite_bytes_sec_max_length
element is the maximum duration in seconds for the
write_bytes_sec_max burst period. Only valid
when the write_bytes_sec_max is set.total_iops_sec_max_lengthtotal_iops_sec_max_length
element is the maximum duration in seconds for the
total_iops_sec_max burst period. Only valid
when the total_iops_sec_max is set.read_iops_sec_max_lengthread_iops_sec_max_length
element is the maximum duration in seconds for the
read_iops_sec_max burst period. Only valid
when the read_iops_sec_max is set.write_iops_sec_maxwrite_iops_sec_max_length
element is the maximum duration in seconds for the
write_iops_sec_max burst period. Only valid
when the write_iops_sec_max is set.
Throughput length since 2.4.0 and QEMU 2.6
drivername attribute selects the primary
backend driver name, while the optional type
attribute provides the sub-type. For example, xen
supports a name of "tap", "tap2", "phy", or "file", with a
type of "aio", while qemu only supports a name of "qemu",
but multiple types including "raw", "bochs", "qcow2", and
"qed".
cache attribute controls the
cache mechanism, possible values are "default", "none",
"writethrough", "writeback", "directsync" (like
"writethrough", but it bypasses the host page cache) and
"unsafe" (host may cache all disk io, and sync requests from
guest are ignored).
Since 0.6.0,
"directsync" since 0.9.5,
"unsafe" since 0.9.7
error_policy attribute controls
how the hypervisor will behave on a disk read or write
error, possible values are "stop", "report", "ignore", and
"enospace".Since 0.8.0, "report" since
0.9.7 The default is left to the discretion of the
hypervisor. There is also an
optional rerror_policy that controls behavior
for read errors only. Since
0.9.7. If no rerror_policy is given, error_policy
is used for both read and write errors. If rerror_policy
is given, it overrides the error_policy for
read errors. Also note that "enospace" is not a valid
policy for read errors, so if error_policy is
set to "enospace" and no rerror_policy is
given, the read error policy will be left at its default.
io attribute controls specific
policies on I/O; qemu guests support "threads" and
"native". Since 0.8.8
ioeventfd attribute allows users to
set
domain I/O asynchronous handling for disk device.
The default is left to the discretion of the hypervisor.
Accepted values are "on" and "off". Enabling this allows
qemu to execute VM while a separate thread handles I/O.
Typically guests experiencing high system CPU utilization
during I/O will benefit from this. On the other hand,
on overloaded host it could increase guest I/O latency.
Since 0.9.3 (QEMU and KVM only)
In general you should leave this option alone, unless you
are very certain you know what you are doing.
event_idx attribute controls
some aspects of device event processing. The value can be
either 'on' or 'off' - if it is on, it will reduce the
number of interrupts and exits for the guest. The default
is determined by QEMU; usually if the feature is
supported, default is on. In case there is a situation
where this behavior is suboptimal, this attribute provides
a way to force the feature off.
Since 0.9.5 (QEMU and KVM only)
In general you should leave this option alone, unless you
are very certain you know what you are doing.
copy_on_read attribute controls
whether to copy read backing file into the image file. The
value can be either "on" or "off".
Copy-on-read avoids accessing the same backing file sectors
repeatedly and is useful when the backing file is over a slow
network. By default copy-on-read is off.
Since 0.9.10 (QEMU and KVM only)
discard attribute controls whether
discard requests (also known as "trim" or "unmap") are
ignored or passed to the filesystem. The value can be either
"unmap" (allow the discard request to be passed) or "ignore"
(ignore the discard request).
Since 1.0.6 (QEMU and KVM only)
detect_zeroes attribute controls whether
to detect zero write requests. The value can be "off", "on" or
"unmap". First two values turn the detection off and on,
respectively. The third value ("unmap") turns the detection on
and additionally tries to discard such areas from the image based
on the value of discard above (it will act as "on"
if discard is set to "ignore"). NB enabling the
detection is a compute intensive operation, but can save file
space and/or time on slow media.
Since 2.0.0
iothread attribute assigns the
disk to an IOThread as defined by the range for the domain
iothreads
value. Multiple disks may be assigned to the same IOThread and
are numbered from 1 to the domain iothreads value. Available
for a disk device target configured to use "virtio"
bus and "pci" or "ccw" address types.
Since 1.2.8 (QEMU 2.1)
queues attribute specifies the number of
virt queues for virtio-blk. (Since 3.9.0)
backenddomainbackenddomain element allows specifying a
backend domain (aka driver domain) hosting the disk. Use the
name attribute to specify the backend domain name.
Since 1.2.13 (Xen only)
bootorder
attribute determines the order in which devices will be tried during
boot sequence. On the S390 architecture only the first boot device is
used. The optional loadparm attribute is an 8 character
string which can be queried by guests on S390 via sclp or diag 308.
Linux guests on S390 can use loadparm to select a boot
entry. Since 3.5.0
The per-device boot elements cannot be used together
with general boot elements in
BIOS bootloader section.
Since 0.8.8
encryptionencryption element is preferred to be a sub-element
of the source element. If present, specifies how the
volume is encrypted using "qcow". See the
Storage Encryption page
for more information.
readonlydevice='cdrom'.
shareabletransientserial<serial>WD-WMAP9A966149</serial>.
Not supported for scsi-block devices, that is those using
disk type 'block' using device 'lun'
on bus 'scsi'.
Since 0.7.1
wwnvendorproductaddressaddress element ties the disk
to a given slot of a controller (the
actual <controller> device can often be
inferred by libvirt, although it can
be explicitly specified).
The type attribute is mandatory, and is typically
"pci" or "drive". For a "pci" controller, additional
attributes for bus, slot,
and function must be present, as well as
optional domain and multifunction.
Multifunction defaults to 'off'; any other value requires
QEMU 0.1.3 and libvirt 0.9.7. For a
"drive" controller, additional attributes
controller, bus, target
(libvirt 0.9.11), and unit
are available, each defaulting to 0.
authauth element is preferred to be a sub-element of
the source element. The element is still read and
managed as a disk sub-element. It is invalid to use
auth as both a sub-element of disk
and source. The auth element was
introduced as a disk sub-element in
libvirt 0.9.7.
geometrygeometry element provides the
ability to override geometry settings. This mostly useful for
S390 DASD-disks or older DOS-disks. 0.10.0
cylscyls attribute is the
number of cylinders. headsheads attribute is the
number of heads. secssecs attribute is the
number of sectors per track. transtrans attribute is the
BIOS-Translation-Modus (none, lba or auto)blockioblockio element allows
to override any of the block device properties listed below.
Since 0.10.2 (QEMU and KVM)
logical_block_sizephysical_block_sizeA directory on the host that can be accessed directly from the guest. since 0.3.3, since 0.8.5 for QEMU/KVM
...
<devices>
<filesystem type='template'>
<source name='my-vm-template'/>
<target dir='/'/>
</filesystem>
<filesystem type='mount' accessmode='passthrough' multidevs='remap'>
<driver type='path' wrpolicy='immediate'/>
<source dir='/export/to/guest'/>
<target dir='/import/from/host'/>
<readonly/>
</filesystem>
<filesystem type='file' accessmode='passthrough'>
<driver type='loop' format='raw'/>
<driver type='path' wrpolicy='immediate'/>
<source file='/export/to/guest.img'/>
<target dir='/import/from/host'/>
<readonly/>
</filesystem>
<filesystem type='mount' accessmode='passthrough'>
<driver type='virtiofs' queue='1024'/>
<binary path='/usr/libexec/virtiofsd' xattr='on'>
<cache mode='always'/>
<lock posix='on' flock='on'/>
</binary>
<source dir='/path'/>
<target dir='mount_tag'/>
</filesystem>
...
</devices>
...
filesystemtype specifies the type of the
source. The possible values are:
mounttype if one is not specified.
This mode also has an optional
sub-element driver, with an
attribute type='path'
or type='handle' (since
0.9.7). The driver block has an optional attribute
wrpolicy that further controls interaction with
the host page cache; omitting the attribute gives default behavior,
while the value immediate means that a host writeback
is immediately triggered for all pages touched during a guest file
write operation (since 0.9.10).
Since 6.2.0, type='virtiofs'
is also supported. Using virtiofs requires setting up shared memory,
see the guide: Virtio-FS
templatefileblockramusage
which gives the memory usage limit in KiB, unless units
are specified by the units attribute. Only used
by LXC driver.
(since 0.9.13)bindaccessmode
which specifies the security mode for accessing the source
(since 0.8.5). Currently this only works
with type='mount' for the QEMU/KVM driver.
For driver type virtiofs, only passthrough is
supported. For other driver types, the possible
values are:
passthroughsource is accessed with the permissions of the
user inside the guest. This is the default accessmode if
one is not specified.
More info
mappedsource is accessed with the permissions of the
hypervisor (QEMU process).
More info
squash
Since 5.2.0, the filesystem element
has an optional attribute model with supported values
"virtio-transitional", "virtio-non-transitional", or "virtio".
See Virtio transitional devices
for more details.
The filesystem element has an optional attribute multidevs
which specifies how to deal with a filesystem export containing more than
one device, in order to avoid file ID collisions on guest when using 9pfs
(since 6.3.0, requires QEMU 4.2).
This attribute is not available for virtiofs. The possible values are:
defaultwarn).
remapforbidwarn
The filesystem element may contain the following subelements:
drivertype attribute selects the primary
backend driver name, while the format
attribute provides the format type. For example, LXC
supports a type of "loop", with a format of "raw" or
"nbd" with any format. QEMU supports a type of "path"
or "handle", but no formats. Virtuozzo driver supports
a type of "ploop" with a format of "ploop".
virtiofs, the queue attribute can be used
to specify the queue size (i.e. how many requests can the queue fit).
(Since 6.2.0)
binarybinary element can tune the options for virtiofsd.
All of the following attributes and elements are optional.
The attribute path can be used to override the path to the daemon.
Attribute xattr enables the use of filesystem extended attributes.
Caching can be tuned via the cache element, possible mode
values being none and always.
Locking can be controlled via the lock
element - attributes posix and flock both accepting
values on or off.
(Since 6.2.0)
sourcename attribute must be used with
type='template', and the dir attribute must
be used with type='mount'. The usage attribute
is used with type='ram' to set the memory limit in KiB,
unless units are specified by the units attribute.
targetsource can be accessed in the guest. For
most drivers this is an automatic mount point, but for QEMU/KVM
this is merely an arbitrary string tag that is exported to the
guest as a hint for where to mount.
readonlyspace_hard_limitspace_soft_limit
Many devices have an optional <address>
sub-element to describe where the device is placed on the
virtual bus presented to the guest. If an address (or any
optional attribute within an address) is omitted on
input, libvirt will generate an appropriate address; but an
explicit address is required if more control over layout is
required. See below for device examples including an address
element.
Every address has a mandatory attribute type that
describes which bus the device is on. The choice of which
address to use for a given device is constrained in part by the
device and the architecture of the guest. For example,
a <disk> device
uses type='drive', while
a <console> device would
use type='pci' on i686 or x86_64 guests,
or type='spapr-vio' on PowerPC64 pseries guests.
Each address type has further optional attributes that control
where on the bus the device will be placed:
pcidomain (a 2-byte hex integer, not
currently used by qemu), bus (a hex value between
0 and 0xff, inclusive), slot (a hex value between
0x0 and 0x1f, inclusive), and function (a value
between 0 and 7, inclusive). Also available is
the multifunction attribute, which controls
turning on the multifunction bit for a particular
slot/function in the PCI control register
(since 0.9.7, requires QEMU
0.13). multifunction defaults to 'off',
but should be set to 'on' for function 0 of a slot that will
have multiple functions used.
(Since 4.10.0), PCI address extensions
depending on the architecture are supported. For example, PCI
addresses for S390 guests will have a zpci child
element, with two attributes: uid (a hex value
between 0x0001 and 0xffff, inclusive), and fid (a
hex value between 0x00000000 and 0xffffffff, inclusive) used by
PCI devices on S390 for User-defined Identifiers and Function
Identifiers.<address type='pci'/>
element with no other attributes as an explicit request to
assign a PCI address for the device rather than some other
type of address that may also be appropriate for that same
device (e.g. virtio-mmio).
drivecontroller (a 2-digit controller
number), bus (a 2-digit bus number),
target (a 2-digit target number),
and unit (a 2-digit unit number on the bus).
virtio-serialcontroller (a 2-digit controller
number), bus (a 2-digit bus number),
and slot (a 2-digit slot within the bus).
ccidbus (a 2-digit bus
number), and slot attribute (a 2-digit slot
within the bus). Since 0.8.8.
usbbus (a hex value between 0 and 0xfff,
inclusive), and port (a dotted notation of up to
four octets, such as 1.2 or 2.1.3.1).
spapr-vioreg (the hex value address
of the starting register). Since
0.9.9.
ccwmachine value of
s390-ccw-virtio use the native CCW bus for I/O devices.
CCW bus addresses have the following additional attributes:
cssid (a hex value between 0 and 0xfe, inclusive),
ssid (a value between 0 and 3, inclusive) and
devno (a hex value between 0 and 0xffff, inclusive).
Partially specified bus addresses are not allowed.
If omitted, libvirt will assign a free bus address with
cssid=0xfe and ssid=0. Virtio-ccw devices must have their cssid
set to 0xfe.
Since 1.0.4
virtio-mmioarmv7l and
aarch64 virtual machines. virtio-mmio addresses
do not have any additional attributes.
Since 1.1.3aarch64 and the machine
type is virt, libvirt will automatically assign PCI
addresses to devices; however, the presence of a single device
with virtio-mmio address in the guest configuration will cause
libvirt to assign virtio-mmio addresses to all further devices.
Since 3.0.0
isaiobase and irq.
Since 1.2.1
unassigned<address type='unassigned'/>
allows the admin to include a PCI hostdev in the domain XML definition,
without making it available for the guest. This allows for configurations
in which Libvirt manages the device as a regular PCI hostdev,
regardless of whether the guest will have access to it.
<address type='unassigned'/> is an invalid address
type for all other device types.
Since 6.0.0
QEMU's virtio devices have some attributes related to the virtio transport under
the driver element:
The iommu attribute enables the use of emulated IOMMU
by the device. The attribute ats controls the Address
Translation Service support for PCIe devices. This is needed to make use
of IOTLB support (see IOMMU device).
Possible values are on or off.
Since 3.5.0
The attribute packed controls if QEMU should try to use
packed virtqueues. Compared to regular split queues, packed queues
consist of only a single descriptor ring replacing available and used
ring, index and descriptor buffer. This can result in better cache
utilization and performance. If packed virtqueues are actually used
depends on the feature negotiation between QEMU, vhost backends and guest
drivers. Possible values are on or off.
Since 6.3.0 (QEMU and KVM only)
Since 5.2.0, some of QEMU's virtio devices,
when used with PCI/PCIe machine types, accept the following
model values:
virtio-transitionalvirtio-non-transitionalvirtiovirtio-non-transitional
device when plugged into a PCI Express slot, and like a
virtio-transitional device otherwise; libvirt will
pick one or the other based on the machine type. This is the best
choice when compatibility with libvirt versions older than 5.2.0
is necessary, but it's otherwise not recommended to use it.
While the information outlined above applies to most virtio devices, there are a few exceptions:
virtio-scsi must be used instead
of virtio for backwards compatibility reasons;
virtio, which will result in a non-transitional device.
For more details see the qemu patch posting and the virtio-1.0 spec.
Depending on the guest architecture, some device buses can appear more than once, with a group of virtual devices tied to a virtual controller. Normally, libvirt can automatically infer such controllers without requiring explicit XML markup, but sometimes it is necessary to provide an explicit controller element, notably when planning the PCI topology for guests where device hotplug is expected.
...
<devices>
<controller type='ide' index='0'/>
<controller type='virtio-serial' index='0' ports='16' vectors='4'/>
<controller type='virtio-serial' index='1'>
<address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
</controller>
<controller type='scsi' index='0' model='virtio-scsi'>
<driver iothread='4'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
</controller>
<controller type='xenbus' maxGrantFrames='64' maxEventChannels='2047'/>
...
</devices>
...
Each controller has a mandatory attribute type,
which must be one of 'ide', 'fdc', 'scsi', 'sata', 'usb',
'ccid', 'virtio-serial' or 'pci', and a mandatory
attribute index which is the decimal integer
describing in which order the bus controller is encountered (for
use in controller attributes of
<address> elements).
Since 1.3.5 the index is optional; if
not specified, it will be auto-assigned to be the lowest unused
index for the given controller type. Some controller types have
additional attributes that control specific features, such as:
virtio-serialvirtio-serial controller has two additional
optional attributes ports and vectors,
which control how many devices can be connected through the
controller. Since 5.2.0, it
supports an optional attribute model which can
be 'virtio', 'virtio-transitional', or 'virtio-non-transitional'. See
Virtio transitional devices
for more details.
scsiscsi controller has an optional attribute
model, which is one of 'auto', 'buslogic', 'ibmvscsi',
'lsilogic', 'lsisas1068', 'lsisas1078', 'virtio-scsi',
'vmpvscsi', 'virtio-transitional', 'virtio-non-transitional'. See
Virtio transitional devices
for more details.
usbusb controller has an optional attribute
model, which is one of "piix3-uhci", "piix4-uhci",
"ehci", "ich9-ehci1", "ich9-uhci1", "ich9-uhci2", "ich9-uhci3",
"vt82c686b-uhci", "pci-ohci", "nec-xhci", "qusb1" (xen pvusb
with qemu backend, version 1.1), "qusb2" (xen pvusb with qemu
backend, version 2.0) or "qemu-xhci". Additionally,
since 0.10.0, if the USB bus needs to
be explicitly disabled for the guest, model='none'
may be used. Since 1.0.5, no default
USB controller will be built on s390.
Since 1.3.5, USB controllers accept a
ports attribute to configure how many devices can be
connected to the controller.ideide controller has an optional attribute
model, which is one of "piix3", "piix4" or "ich6".xenbusxenbus
controller has an optional attribute maxGrantFrames,
which specifies the maximum number of grant frames the controller
makes available for connected devices.
Since 6.3.0, the xenbus controller
supports the optional maxEventChannels attribute,
which specifies maximum number of event channels (PV interrupts)
that can be used by the guest.Note: The PowerPC64 "spapr-vio" addresses do not have an associated controller.
For controllers that are themselves devices on a PCI or USB bus,
an optional sub-element <address> can specify
the exact relationship of the controller to its master bus, with
semantics given above.
An optional sub-element driver can specify the driver
specific options:
queuesqueues attribute specifies the number of
queues for the controller. For best performance, it's recommended to
specify a value matching the number of vCPUs.
Since 1.0.5 (QEMU and KVM only)
cmd_per_luncmd_per_lun attribute specifies the maximum
number of commands that can be queued on devices controlled by the
host.
Since 1.2.7 (QEMU and KVM only)
max_sectorsmax_sectors attribute specifies the maximum
amount of data in bytes that will be transferred to or from the device
in a single command. The transfer length is measured in sectors, where
a sector is 512 bytes.
Since 1.2.7 (QEMU and KVM only)
ioeventfdioeventfd attribute specifies
whether the controller should use
I/O asynchronous handling or not. Accepted values are
"on" and "off". Since 1.2.18
iothreadscsi using model
virtio-scsi for address types
pci and ccw
since 1.3.5 (QEMU 2.4).
The optional iothread attribute assigns the controller
to an IOThread as defined by the range for the domain
iothreads
value. Each SCSI disk assigned to use the specified
controller will utilize the same IOThread. If a specific
IOThread is desired for a specific SCSI disk, then
multiple controllers must be defined each having a specific
iothread value. The iothread value
must be within the range 1 to the domain iothreads value.
USB companion controllers have an optional
sub-element <master> to specify the exact
relationship of the companion to its master controller.
A companion controller is on the same bus as its master, so
the companion index value should be equal.
Not all controller models can be used as companion controllers
and libvirt might provide some sensible defaults (settings
of master startport and function of an
address) for some particular models.
Preferred companion controllers are ich-uhci[123].
...
<devices>
<controller type='usb' index='0' model='ich9-ehci1'>
<address type='pci' domain='0' bus='0' slot='4' function='7'/>
</controller>
<controller type='usb' index='0' model='ich9-uhci1'>
<master startport='0'/>
<address type='pci' domain='0' bus='0' slot='4' function='0' multifunction='on'/>
</controller>
...
</devices>
...
PCI controllers have an optional model attribute; possible
values for this attribute are
pci-root, pci-bridge
(since 1.0.5)
pcie-root, dmi-to-pci-bridge
(since 1.1.2)
pcie-root-port, pcie-switch-upstream-port,
pcie-switch-downstream-port
(since 1.2.19)
pci-expander-bus, pcie-expander-bus
(since 1.3.4)
pcie-to-pci-bridge
(since 4.3.0)
The root controllers (pci-root
and pcie-root) have an
optional pcihole64 element specifying how big (in
kilobytes, or in the unit specified by pcihole64's
unit attribute) the 64-bit PCI hole should be. Some guests (like
Windows XP or Windows Server 2003) might crash when QEMU and Seabios
are recent enough to support 64-bit PCI holes, unless this is disabled
(set to 0). Since 1.1.2 (QEMU only)
PCI controllers also have an optional
subelement <model> with an attribute
name. The name attribute holds the name of the
specific device that qemu is emulating (e.g. "i82801b11-bridge")
rather than simply the class of device ("pcie-to-pci-bridge",
"pci-bridge"), which is set in the controller element's
model attribute. In almost all cases, you should not
manually add a <model> subelement to a
controller, nor should you modify one that is automatically
generated by libvirt. Since 1.2.19 (QEMU
only).
PCI controllers also have an optional
subelement <target> with the attributes and
subelements listed below. These are configurable items that 1)
are visible to the guest OS so must be preserved for guest ABI
compatibility, and 2) are usually left to default values or
derived automatically by libvirt. In almost all cases, you
should not manually add a <target> subelement
to a controller, nor should you modify the values in the those
that are automatically generated by
libvirt. Since 1.2.19 (QEMU only).
chassisNrchassisNr attribute in
the <target> subelement, which is used to
control QEMU's "chassis_nr" option for the pci-bridge device
(normally libvirt automatically sets this to the same value as
the index attribute of the pci controller). If set, chassisNr
must be between 1 and 255.
chassischassis attribute in
the <target> subelement, which is used to
set the controller's "chassis" configuration value, which is
visible to the virtual machine. If set, chassis must be
between 0 and 255.
portport attribute in
the <target> subelement, which
is used to set the controller's "port" configuration value,
which is visible to the virtual machine. If set, port must be
between 0 and 255.
busNrbusNr attribute (1-254). This will be
the bus number of the new bus; All bus numbers between that
specified and 255 will be available only for assignment to
PCI/PCIe controllers plugged into the hierarchy starting with
this expander bus, and bus numbers less than the specified
value will be available to the next lower expander-bus (or the
root-bus if there are no lower expander buses). If you do not
specify a busNumber, libvirt will find the lowest existing
busNumber in all other expander buses (or use 256 if there are
no others) and auto-assign the busNr of that found bus - 2,
which provides one bus number for the pci-expander-bus and one
for the pci-bridge that is automatically attached to it (if
you plan on adding more pci-bridges to the hierarchy of the
bus, you should manually set busNr to a lower value).
A similar algorithm is used for automatically determining the busNr attribute for pcie-expander-bus, but since the pcie-expander-bus doesn't have any built-in pci-bridge, the 2nd bus-number is just being reserved for the pcie-root-port that must necessarily be connected to the bus in order to actually plug in an endpoint device. If you intend to plug multiple devices into a pcie-expander-bus, you must connect a pcie-switch-upstream-port to the pcie-root-port that is plugged into the pcie-expander-bus, and multiple pcie-switch-downstream-ports to the pcie-switch-upstream-port, and of course for this to work properly, you will need to decrease the pcie-expander-bus' busNr accordingly so that there are enough unused bus numbers above it to accommodate giving out one bus number for the upstream-port and one for each downstream-port (in addition to the pcie-root-port and the pcie-expander-bus itself).
nodepci-expander-bus for the pc
machine type, pcie-expander-bus for the q35 machine
type and, since 3.6.0,
pci-root for the pseries machine type) can have an
optional <node> subelement within
the <target> subelement, which is used to
set the NUMA node reported to the guest OS for that bus - the
guest OS will then know that all devices on that bus are a
part of the specified NUMA node (it is up to the user of the
libvirt API to attach host devices to the correct
pci-expander-bus when assigning them to the domain).
indexFor machine types which provide an implicit PCI bus, the pci-root controller with index=0 is auto-added and required to use PCI devices. pci-root has no address. PCI bridges are auto-added if there are too many devices to fit on the one bus provided by pci-root, or a PCI bus number greater than zero was specified. PCI bridges can also be specified manually, but their addresses should only refer to PCI buses provided by already specified PCI controllers. Leaving gaps in the PCI controller indexes might lead to an invalid configuration.
...
<devices>
<controller type='pci' index='0' model='pci-root'/>
<controller type='pci' index='1' model='pci-bridge'>
<address type='pci' domain='0' bus='0' slot='5' function='0' multifunction='off'/>
</controller>
</devices>
...
For machine types which provide an implicit PCI Express (PCIe)
bus (for example, the machine types based on the Q35 chipset),
the pcie-root controller with index=0 is auto-added to the
domain's configuration. pcie-root has also no address, provides
31 slots (numbered 1-31) that can be used to attach PCIe or PCI
devices (although libvirt will never auto-assign a PCI device to
a PCIe slot, it will allow manual specification of such an
assignment). Devices connected to pcie-root cannot be
hotplugged. If traditional PCI devices are present in the guest
configuration, a pcie-to-pci-bridge controller will
automatically be added: this controller, which plugs into a
pcie-root-port, provides 31 usable PCI slots (1-31) with
hotplug support (since 4.3.0). If the QEMU
binary doesn't support the corresponding device, then a
dmi-to-pci-bridge controller will be added instead,
usually at the defacto standard location of slot=0x1e. A
dmi-to-pci-bridge controller plugs into a PCIe slot (as provided
by pcie-root), and itself provides 31 standard PCI slots (which
also do not support device hotplug). In order to have
hot-pluggable PCI slots in the guest system, a pci-bridge
controller will also be automatically created and connected to
one of the slots of the auto-created dmi-to-pci-bridge
controller; all guest PCI devices with addresses that are
auto-determined by libvirt will be placed on this pci-bridge
device. (since 1.1.2).
Domains with an implicit pcie-root can also add controllers
with model='pcie-root-port',
model='pcie-switch-upstream-port',
and model='pcie-switch-downstream-port'. pcie-root-port
is a simple type of bridge device that can connect only to one
of the 31 slots on the pcie-root bus on its upstream side, and
makes a single (PCIe, hotpluggable) port available on the
downstream side (at slot='0'). pcie-root-port can be used to
provide a single slot to later hotplug a PCIe device (but is not
itself hotpluggable - it must be in the configuration when the
domain is started).
(since 1.2.19)
pcie-switch-upstream-port is a more flexible (but also more complex) device that can only plug into a pcie-root-port or pcie-switch-downstream-port on the upstream side (and only before the domain is started - it is not hot-pluggable), and provides 32 ports on the downstream side (slot='0' - slot='31') that accept only pcie-switch-downstream-port devices; each pcie-switch-downstream-port device can only plug into a pcie-switch-upstream-port on its upstream side (again, not hot-pluggable), and on its downstream side provides a single hotpluggable pcie port that can accept any standard pci or pcie device (or another pcie-switch-upstream-port), i.e. identical in function to a pcie-root-port. (since 1.2.19)
...
<devices>
<controller type='pci' index='0' model='pcie-root'/>
<controller type='pci' index='1' model='pcie-root-port'>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/>
</controller>
<controller type='pci' index='2' model='pcie-to-pci-bridge'>
<address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
</controller>
</devices>
...
When using a lock manager, it may be desirable to record device leases against a VM. The lock manager will ensure the VM won't start unless the leases can be acquired.
...
<devices>
...
<lease>
<lockspace>somearea</lockspace>
<key>somekey</key>
<target path='/some/lease/path' offset='1024'/>
</lease>
...
</devices>
...
lockspacekeytarget
USB, PCI and SCSI devices attached to the host can be passed through
to the guest using the hostdev element.
since after 0.4.4 for USB, 0.6.0 for PCI (KVM only)
and 1.0.6 for SCSI (KVM only):
...
<devices>
<hostdev mode='subsystem' type='usb'>
<source startupPolicy='optional'>
<vendor id='0x1234'/>
<product id='0xbeef'/>
</source>
<boot order='2'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='pci' managed='yes'>
<source>
<address domain='0x0000' bus='0x06' slot='0x02' function='0x0'/>
</source>
<boot order='1'/>
<rom bar='on' file='/etc/fake/boot.bin'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='scsi' sgio='filtered' rawio='yes'>
<source>
<adapter name='scsi_host0'/>
<address bus='0' target='0' unit='0'/>
</source>
<readonly/>
<address type='drive' controller='0' bus='0' target='0' unit='0'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='scsi'>
<source protocol='iscsi' name='iqn.2014-08.com.example:iscsi-nopool/1'>
<host name='example.com' port='3260'/>
<auth username='myuser'>
<secret type='iscsi' usage='libvirtiscsi'/>
</auth>
</source>
<address type='drive' controller='0' bus='0' target='0' unit='0'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='scsi_host'>
<source protocol='vhost' wwpn='naa.50014057667280d8'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='mdev' model='vfio-pci'>
<source>
<address uuid='c2177883-f1bb-47f0-914d-32a22e3a8804'/>
</source>
</hostdev>
<hostdev mode='subsystem' type='mdev' model='vfio-ccw'>
<source>
<address uuid='9063cba3-ecef-47b6-abcf-3fef4fdcad85'/>
</source>
<address type='ccw' cssid='0xfe' ssid='0x0' devno='0x0001'/>
</hostdev>
</devices>
...
hostdevhostdev element is the main container for describing
host devices. For each device, the mode is always
"subsystem" and the type is one of the following values
with additional attributes noted.
usbpcimanaged is "yes" it is
detached from the host before being passed on to the guest
and reattached to the host after the guest exits. If
managed is omitted or "no", the user is
responsible to call virNodeDeviceDetachFlags
(or virsh nodedev-detach before starting the guest
or hot-plugging the device and virNodeDeviceReAttach
(or virsh nodedev-reattach) after hot-unplug or
stopping the guest.
scsisgio (since 1.0.6)
attribute indicates whether unprivileged SG_IO commands are
filtered for the disk. Valid settings are "filtered" or
"unfiltered", where the default is "filtered".
The optional rawio
(since 1.2.9) attribute indicates
whether the lun needs the rawio capability. Valid settings are
"yes" or "no". See the rawio description within the
disk section.
If a disk lun in the domain already has the rawio capability,
then this setting not required.
scsi_hosttype passes all LUNs presented by a single HBA to
the guest. Since 5.2.0, the
model attribute can be specified further
with "virtio-transitional", "virtio-non-transitional", or
"virtio". See
Virtio transitional devices
for more details.
mdevmodel attribute specifies the device API which
determines how the host's vfio driver will expose the device to the
guest. Currently, model='vfio-pci',
model='vfio-ccw' (Since 4.4.0)
and model='vfio-ap' (Since 4.9.0)
is supported. MDEV section
provides more information about mediated devices as well as how to
create mediated devices on the host.
Since 4.6.0 (QEMU 2.12) an optional
display attribute may be used to enable or disable
support for an accelerated remote desktop backed by a mediated
device (such as NVIDIA vGPU or Intel GVT-g) as an alternative to
emulated video devices. This attribute
is limited to model='vfio-pci' only. Supported values
are either on or off (default is 'off').
It is required to use a
graphical framebuffer in order to
use this attribute, currently only supported with VNC, Spice and
egl-headless graphics devices.
Since version 5.10.0, there is an optional
ramfb attribute for devices with
model='vfio-pci'. Supported values are either
on or off (default is 'off'). When
enabled, this attribute provides a memory framebuffer device to the
guest. This framebuffer will be used as a boot display when a vgpu
device is the primary display.
Note: There are also some implications on the usage of guest's
address type depending on the model attribute,
see the address element below.
Note: The managed attribute is only used with
type='pci' and is ignored by all the other device types,
thus setting managed explicitly with other than a PCI
device has the same effect as omitting it. Similarly,
model attribute is only supported by mediated devices and
ignored by all other device types.
sourceusbvendor and product elements
or by the device's address on the host using the
address element.
Since 1.0.0, the source
element of USB devices may contain startupPolicy
attribute which can be used to define policy what to do if the
specified host USB device is not found. The attribute accepts
the following values:
| mandatory | fail if missing for any reason (the default) |
| requisite | fail if missing on boot up, drop if missing on migrate/restore/revert |
| optional | drop if missing at any start attempt |
pciaddress.
scsiadapter
and address elements. The address
element includes a bus attribute (a 2-digit bus
number), a target attribute (a 10-digit target
number), and a unit attribute (a 20-digit unit
number on the bus). Not all hypervisors support larger
target and unit values. It is up
to each hypervisor to determine the maximum value supported
for the adapter.
Since 1.2.8, the source
element of a SCSI device may contain the protocol
attribute. When the attribute is set to "iscsi", the host
device XML follows the network disk
device using the same name attribute and optionally
using the auth element to provide the authentication
credentials to the iSCSI server.
scsi_hostprotocol
attribute set to "vhost" and a wwpn attribute that
is the vhost_scsi wwpn (16 hexadecimal digits with a prefix of
"naa.") established in the host configfs.
mdevaddress element. The
address element contains a single mandatory attribute
uuid.
vendor, productvendor and product elements each have an
id attribute that specifies the USB vendor and product id.
The ids can be given in decimal, hexadecimal (starting with 0x) or
octal (starting with 0) form.bootorder
attribute determines the order in which devices will be tried during
boot sequence. The per-device boot elements cannot be
used together with general boot elements in
BIOS bootloader section.
Since 0.8.8 for PCI devices,
Since 1.0.1 for USB devices.
romrom element is used to change how a PCI
device's ROM is presented to the guest. The optional bar
attribute can be set to "on" or "off", and determines whether
or not the device's ROM will be visible in the guest's memory
map. (In PCI documentation, the "rombar" setting controls the
presence of the Base Address Register for the ROM). If no rom
bar is specified, the qemu default will be used (older
versions of qemu used a default of "off", while newer qemus
have a default of "on"). Since
0.9.7 (QEMU and KVM only). The optional
file attribute contains an absolute path to a binary file
to be presented to the guest as the device's ROM BIOS. This
can be useful, for example, to provide a PXE boot ROM for a
virtual function of an sr-iov capable ethernet device (which
has no boot ROMs for the VFs).
Since 0.9.10 (QEMU and KVM only).
The optional enabled attribute can be set to
no to disable PCI ROM loading completely for the device;
if PCI ROM loading is disabled through this attribute, attempts to
tweak the loading process further using the bar or
file attributes will be rejected.
Since 4.3.0 (QEMU and KVM only).
addressaddress element for USB devices has a
bus and device attribute to specify the
USB bus and device number the device appears at on the host.
The values of these attributes can be given in decimal, hexadecimal
(starting with 0x) or octal (starting with 0) form.
For PCI devices the element carries 4 attributes allowing to designate
the device as can be found with the lspci or
with virsh nodedev-list. For SCSI devices a 'drive'
address type must be used. For mediated devices, which are software-only
devices defining an allocation of resources on the physical parent device,
the address type used must conform to the model attribute
of element hostdev, e.g. any address type other than PCI for
vfio-pci device API or any address type other than CCW for
vfio-ccw device API will result in an error.
See above for more details on the address
element.driverdriver
subelement that specifies which backend driver to use for PCI
device assignment. Use the name attribute to
select either "vfio" (for the new VFIO device assignment
backend, which is compatible with UEFI SecureBoot) or "kvm"
(the legacy device assignment handled directly by the KVM
kernel module)Since 1.0.5 (QEMU and KVM
only, requires kernel 3.6 or newer). When specified,
device assignment will fail if the requested method of device
assignment isn't available on the host. When not specified,
the default is "vfio" on systems where the VFIO driver is
available and loaded, and "kvm" on older systems, or those
where the VFIO driver hasn't been
loaded Since 1.1.3 (prior to that
the default was always "kvm").
readonlyshareable
Note: Although shareable was introduced
in 1.0.6, it did not work as
as expected until 1.2.2.
Block / character devices from the host can be passed through
to the guest using the hostdev element. This is
only possible with container based virtualization. Devices are specified
by a fully qualified path.
since after 1.0.1 for LXC:
...
<hostdev mode='capabilities' type='storage'>
<source>
<block>/dev/sdf1</block>
</source>
</hostdev>
...
...
<hostdev mode='capabilities' type='misc'>
<source>
<char>/dev/input/event3</char>
</source>
</hostdev>
...
...
<hostdev mode='capabilities' type='net'>
<source>
<interface>eth0</interface>
</source>
</hostdev>
...
hostdevhostdev element is the main container for describing
host devices. For block/character device passthrough mode is
always "capabilities" and type is "storage" for a block
device, "misc" for a character device and "net" for a host network
interface.
sourceUSB device redirection through a character device is supported since after 0.9.5 (KVM only):
...
<devices>
<redirdev bus='usb' type='tcp'>
<source mode='connect' host='localhost' service='4000'/>
<boot order='1'/>
</redirdev>
<redirfilter>
<usbdev class='0x08' vendor='0x1234' product='0xbeef' version='2.56' allow='yes'/>
<usbdev allow='no'/>
</redirfilter>
</devices>
...
redirdevredirdev element is the main container for
describing redirected devices. bus must be "usb"
for a USB device.
An additional attribute type is required,
matching one of the
supported serial device types,
to describe the host side of the
tunnel; type='tcp'
or type='spicevmc' (which uses the usbredir
channel of a SPICE graphics
device) are typical. The redirdev element has an optional
sub-element <address> which can tie the
device to a particular controller. Further sub-elements,
such as <source>, may be required according
to the given type, although a <target> sub-element
is not required (since the consumer of the character device is
the hypervisor itself, rather than a device visible in the guest).
bootorder attribute determines the order in which
devices will be tried during boot sequence. The per-device
boot elements cannot be used together with general
boot elements in BIOS bootloader section.
(Since 1.0.1)
redirfilter redirfilter element is used for creating the
filter rule to filter out certain devices from redirection.
It uses sub-element <usbdev> to define each filter rule.
class attribute is the USB Class code, for example,
0x08 represents mass storage devices. The USB device can be addressed by
vendor / product id using the vendor and product attributes.
version is the device revision from the bcdDevice field (not
the version of the USB protocol).
These four attributes are optional and -1 can be used to allow
any value for them. allow attribute is mandatory,
'yes' means allow, 'no' for deny.
A virtual smartcard device can be supplied to the guest via the
smartcard element. A USB smartcard reader device on
the host cannot be used on a guest with simple device
passthrough, since it will then not be available on the host,
possibly locking the host computer when it is "removed".
Therefore, some hypervisors provide a specialized virtual device
that can present a smartcard interface to the guest, with
several modes for describing how credentials are obtained from
the host or even a from a channel created to a third-party
smartcard provider. Since 0.8.8
...
<devices>
<smartcard mode='host'/>
<smartcard mode='host-certificates'>
<certificate>cert1</certificate>
<certificate>cert2</certificate>
<certificate>cert3</certificate>
<database>/etc/pki/nssdb/</database>
</smartcard>
<smartcard mode='passthrough' type='tcp'>
<source mode='bind' host='127.0.0.1' service='2001'/>
<protocol type='raw'/>
<address type='ccid' controller='0' slot='0'/>
</smartcard>
<smartcard mode='passthrough' type='spicevmc'/>
</devices>
...
The <smartcard> element has a mandatory
attribute mode. The following modes are supported;
in each mode, the guest sees a device on its USB bus that
behaves like a physical USB CCID (Chip/Smart Card Interface
Device) card.
host<address> sub-element.host-certificatescertutil -d /etc/pki/nssdb -x -t
CT,CT,CT -S -s CN=cert1 -n cert1, and the resulting three
certificate names must be supplied as the content of each of
three <certificate> sub-elements. An
additional sub-element <database> can specify
the absolute path to an alternate directory (matching
the -d option of the certutil command
when creating the certificates); if not present, it defaults to
/etc/pki/nssdb.passthroughtype is required, matching one of the
supported serial device types, to
describe the host side of the tunnel; type='tcp'
or type='spicevmc' (which uses the smartcard
channel of a SPICE graphics
device) are typical. Further sub-elements, such
as <source>, may be required according to the
given type, although a <target> sub-element
is not required (since the consumer of the character device is
the hypervisor itself, rather than a device visible in the
guest).
Each mode supports an optional
sub-element <address>, which fine-tunes the
correlation between the smartcard and a ccid bus
controller, documented above.
For now, qemu only supports at most one
smartcard, with an address of bus=0 slot=0.
...
<devices>
<interface type='direct' trustGuestRxFilters='yes'>
<source dev='eth0'/>
<mac address='52:54:00:5d:c7:9e'/>
<boot order='1'/>
<rom bar='off'/>
</interface>
</devices>
...
There are several possibilities for specifying a network interface visible to the guest. Each subsection below provides more details about common setup options.
Since 1.2.10),
the interface element
property trustGuestRxFilters provides the
capability for the host to detect and trust reports from the
guest regarding changes to the interface mac address and receive
filters by setting the attribute to yes. The default
setting for the attribute is no for security
reasons and support depends on the guest network device model as
well as the type of connection on the host - currently it is
only supported for the virtio device model and for macvtap
connections on the host.
Each <interface> element has an
optional <address> sub-element that can tie
the interface to a particular pci slot, with
attribute type='pci'
as documented above.
This is the recommended config for general guest connectivity on
hosts with dynamic / wireless networking configs (or multi-host
environments where the host hardware details are described
separately in a <network>
definition Since 0.9.4).
Provides a connection whose details are described by the named
network definition. Depending on the virtual network's "forward
mode" configuration, the network may be totally isolated
(no <forward> element given), NAT'ing to an
explicit network device or to the default route
(<forward mode='nat'>), routed with no NAT
(<forward mode='route'/>), or connected
directly to one of the host's network interfaces (via macvtap)
or bridge devices ((<forward
mode='bridge|private|vepa|passthrough'/> Since
0.9.4)
For networks with a forward mode of bridge, private, vepa, and
passthrough, it is assumed that the host has any necessary DNS
and DHCP services already setup outside the scope of libvirt. In
the case of isolated, nat, and routed networks, DHCP and DNS are
provided on the virtual network by libvirt, and the IP range can
be determined by examining the virtual network config with
'virsh net-dumpxml [networkname]'. There is one
virtual network called 'default' setup out of the box which does
NAT'ing to the default route and has an IP range
of 192.168.122.0/255.255.255.0. Each guest will
have an associated tun device created with a name of vnetN,
which can also be overridden with the <target> element
(see
overriding the target element).
When the source of an interface is a network,
a portgroup can be specified along with the name of
the network; one network may have multiple portgroups defined,
with each portgroup containing slightly different configuration
information for different classes of network
connections. Since 0.9.4.
When a guest is running an interface of type network
may include a portid attribute. This provides the UUID
of an associated virNetworkPortPtr object that records the association
between the domain interface and the network. This attribute is
read-only since port objects are create and deleted automatically
during startup and shutdown. Since 5.1.0
Also, similar to direct network connections
(described below), a connection of type network may
specify a virtualport element, with configuration
data to be forwarded to a vepa (802.1Qbg) or 802.1Qbh compliant
switch (Since 0.8.2), or to an
Open vSwitch virtual switch (Since
0.9.11).
Since the actual type of switch may vary depending on the
configuration in the <network> on the host,
it is acceptable to omit the virtualport type
attribute, and specify attributes from multiple different
virtualport types (and also to leave out certain attributes); at
domain startup time, a complete <virtualport>
element will be constructed by merging together the type and
attributes defined in the network and the portgroup referenced
by the interface. The newly-constructed virtualport is a combination
of them. The attributes from lower virtualport can't make change
on the ones defined in higher virtualport.
Interface takes the highest priority, portgroup is lowest priority.
(Since 0.10.0). For example, in order
to work properly with both an 802.1Qbh switch and an Open vSwitch
switch, you may choose to specify no type, but both
a profileid (in case the switch is 802.1Qbh) and
an interfaceid (in case the switch is Open vSwitch)
(you may also omit the other attributes, such as managerid,
typeid, or profileid, to be filled in from the
network's <virtualport>). If you want to
limit a guest to connecting only to certain types of switches,
you can specify the virtualport type, but still omit some/all of
the parameters - in this case if the host's network has a
different type of virtualport, connection of the interface will
fail.
...
<devices>
<interface type='network'>
<source network='default'/>
</interface>
...
<interface type='network'>
<source network='default' portgroup='engineering'/>
<target dev='vnet7'/>
<mac address="00:11:22:33:44:55"/>
<virtualport>
<parameters instanceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/>
</virtualport>
</interface>
</devices>
...
This is the recommended config for general guest connectivity on hosts with static wired networking configs.
Provides a bridge from the VM directly to the LAN. This assumes there is a bridge device on the host which has one or more of the hosts physical NICs enslaved. The guest VM will have an associated tun device created with a name of vnetN, which can also be overridden with the <target> element (see overriding the target element). The tun device will be enslaved to the bridge. The IP range / network configuration is whatever is used on the LAN. This provides the guest VM full incoming & outgoing net access just like a physical machine.
On Linux systems, the bridge device is normally a standard Linux
host bridge. On hosts that support Open vSwitch, it is also
possible to connect to an Open vSwitch bridge device by adding
a <virtualport type='openvswitch'/> to the
interface definition. (Since
0.9.11). The Open vSwitch type virtualport accepts two
parameters in its <parameters> element -
an interfaceid which is a standard uuid used to
uniquely identify this particular interface to Open vSwitch (if
you do not specify one, a random interfaceid will be generated
for you when you first define the interface), and an
optional profileid which is sent to Open vSwitch as
the interfaces "port-profile".
...
<devices>
...
<interface type='bridge'>
<source bridge='br0'/>
</interface>
<interface type='bridge'>
<source bridge='br1'/>
<target dev='vnet7'/>
<mac address="00:11:22:33:44:55"/>
</interface>
<interface type='bridge'>
<source bridge='ovsbr'/>
<virtualport type='openvswitch'>
<parameters profileid='menial' interfaceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/>
</virtualport>
</interface>
...
</devices>
...
On hosts that support Open vSwitch on the kernel side and have the
Midonet Host Agent configured, it is also possible to connect to the
'midonet' bridge device by adding a
<virtualport type='midonet'/> to the
interface definition. (Since
1.2.13). The Midonet virtualport type requires an
interfaceid attribute in its
<parameters> element. This interface id is the UUID
that specifies which port in the virtual network topology will be bound
to the interface.
...
<devices>
...
<interface type='bridge'>
<source bridge='br0'/>
</interface>
<interface type='bridge'>
<source bridge='br1'/>
<target dev='vnet7'/>
<mac address="00:11:22:33:44:55"/>
</interface>
<interface type='bridge'>
<source bridge='midonet'/>
<virtualport type='midonet'>
<parameters interfaceid='0b2d64da-3d0e-431e-afdd-804415d6ebbb'/>
</virtualport>
</interface>
...
</devices>
...
Provides a virtual LAN with NAT to the outside world. The virtual
network has DHCP & DNS services and will give the guest VM addresses
starting from 10.0.2.15. The default router will be
10.0.2.2 and the DNS server will be 10.0.2.3.
This networking is the only option for unprivileged users who need their
VMs to have outgoing access. Since 3.8.0
it is possible to override the default network address by
including an ip element specifying an IPv4
address in its one mandatory attribute, address.
Optionally, a second ip element with a
family attribute set to "ipv6" can be
specified to add an IPv6 address to the interface.
address. Optionally, address
prefix can be specified.
...
<devices>
<interface type='user'/>
...
<interface type='user'>
<mac address="00:11:22:33:44:55"/>
<ip family='ipv4' address='172.17.2.0' prefix='24'/>
<ip family='ipv6' address='2001:db8:ac10:fd01::' prefix='64'/>
</interface>
</devices>
...
Provides a means to use a new or existing tap device (or veth device pair, depening on the needs of the hypervisor driver) that is partially or wholly setup external to libvirt (either prior to the guest starting, or while the guest is being started via an optional script specified in the config).
The name of the tap device can optionally be specified with
the dev attribute of the
<target> element. If no target dev is
specified, libvirt will create a new standard tap device with a
name of the pattern "vnetN", where "N" is replaced with a
number. If a target dev is specified and that device doesn't
exist, then a new standard tap device will be created with the
exact dev name given. If the specified target dev does exist,
then that existing device will be used. Usually some basic setup
of the device is done by libvirt, including setting a MAC
address, and the IFF_UP flag, but if the dev is a
pre-existing device, and the managed attribute of
the target element is also set to "no" (the default
value is "yes"), even this basic setup will not be performed -
libvirt will simply pass the device on to the hypervisor with no
setup at all. Since 5.7.0 Using
managed='no' with a pre-created tap device is useful because
it permits a virtual machine managed by an unprivileged libvirtd
to have emulated network devices based on tap devices.
After creating/opening the tap device, an optional shell script
(given in the path attribute of
the <script> element) will be run; this can
be used to do whatever extra host network integration is
required.
...
<devices>
<interface type='ethernet'>
<script path='/etc/qemu-ifup-mynet'/>
</interface>
...
<interface type='ethernet'>
<target dev='mytap1' managed='no'/>
<model type='virtio'/>
</interface>
</devices>
...
Provides direct attachment of the virtual machine's NIC to the given
physical interface of the host.
Since 0.7.7 (QEMU and KVM only)
This setup requires the Linux macvtap
driver to be available. (Since Linux 2.6.34.)
One of the modes 'vepa'
(
'Virtual Ethernet Port Aggregator'), 'bridge' or 'private'
can be chosen for the operation mode of the macvtap device, 'vepa'
being the default mode. The individual modes cause the delivery of
packets to behave as follows:
If the model type is set to virtio and
interface's trustGuestRxFilters attribute is set
to yes, changes made to the interface mac address,
unicast/multicast receive filters, and vlan settings in the
guest will be monitored and propagated to the associated macvtap
device on the host (Since
1.2.10). If trustGuestRxFilters is not set,
or is not supported for the device model in use, an attempted
change to the mac address originating from the guest side will
result in a non-working network connection.
vepabridgevepa mode,
a VEPA capable bridge is required.privateprivate mode.passthrough
...
<devices>
...
<interface type='direct' trustGuestRxFilters='no'>
<source dev='eth0' mode='vepa'/>
</interface>
</devices>
...
The network access of direct attached virtual machines can be managed by the hardware switch to which the physical interface of the host machine is connected to.
The interface can have additional parameters as shown below, if the switch is conforming to the IEEE 802.1Qbg standard. The parameters of the virtualport element are documented in more detail in the IEEE 802.1Qbg standard. The values are network specific and should be provided by the network administrator. In 802.1Qbg terms, the Virtual Station Interface (VSI) represents the virtual interface of a virtual machine. Since 0.8.2
Please note that IEEE 802.1Qbg requires a non-zero value for the VLAN ID.
manageridtypeidtypeidversioninstanceid
...
<devices>
...
<interface type='direct'>
<source dev='eth0.2' mode='vepa'/>
<virtualport type="802.1Qbg">
<parameters managerid="11" typeid="1193047" typeidversion="2" instanceid="09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f"/>
</virtualport>
</interface>
</devices>
...
The interface can have additional parameters as shown below if the switch is conforming to the IEEE 802.1Qbh standard. The values are network specific and should be provided by the network administrator. Since 0.8.2
profileid
...
<devices>
...
<interface type='direct'>
<source dev='eth0' mode='private'/>
<virtualport type='802.1Qbh'>
<parameters profileid='finance'/>
</virtualport>
</interface>
</devices>
...
A PCI network device (specified by the <source> element) is directly assigned to the guest using generic device passthrough, after first optionally setting the device's MAC address to the configured value, and associating the device with an 802.1Qbh capable switch using an optionally specified <virtualport> element (see the examples of virtualport given above for type='direct' network devices). Note that - due to limitations in standard single-port PCI ethernet card driver design - only SR-IOV (Single Root I/O Virtualization) virtual function (VF) devices can be assigned in this manner; to assign a standard single-port PCI or PCIe ethernet card to a guest, use the traditional <hostdev> device definition and Since 0.9.11
To use VFIO device assignment rather than traditional/legacy KVM
device assignment (VFIO is a new method of device assignment
that is compatible with UEFI Secure Boot), a type='hostdev'
interface can have an optional driver sub-element
with a name attribute set to "vfio". To use legacy
KVM device assignment you can set name to "kvm" (or
simply omit the <driver> element, since "kvm"
is currently the default).
Since 1.0.5 (QEMU and KVM only, requires kernel 3.6 or newer)
Note that this "intelligent passthrough" of network devices is very similar to the functionality of a standard <hostdev> device, the difference being that this method allows specifying a MAC address and <virtualport> for the passed-through device. If these capabilities are not required, if you have a standard single-port PCI, PCIe, or USB network card that doesn't support SR-IOV (and hence would anyway lose the configured MAC address during reset after being assigned to the guest domain), or if you are using a version of libvirt older than 0.9.11, you should use standard <hostdev> to assign the device to the guest instead of <interface type='hostdev'/>.
Similar to the functionality of a standard <hostdev> device,
when managed is "yes", it is detached from the host
before being passed on to the guest, and reattached to the host
after the guest exits. If managed is omitted or "no",
the user is responsible to call virNodeDeviceDettach
(or virsh nodedev-detach) before starting the guest
or hot-plugging the device, and virNodeDeviceReAttach
(or virsh nodedev-reattach) after hot-unplug or
stopping the guest.
...
<devices>
<interface type='hostdev' managed='yes'>
<driver name='vfio'/>
<source>
<address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
</source>
<mac address='52:54:00:6d:90:02'/>
<virtualport type='802.1Qbh'>
<parameters profileid='finance'/>
</virtualport>
</interface>
</devices>
...
Since 6.1.0 (QEMU and KVM only, requires
QEMU 4.2.0 or newer and a guest virtio-net driver supporting
the "failover" feature, such as the one included in Linux
kernel 4.18 and newer)
The <teaming> element of two interfaces can
be used to connect them as a team/bond device in the guest
(assuming proper support in the hypervisor and the guest
network driver).
...
<devices>
<interface type='network'>
<source network='mybridge'/>
<mac address='00:11:22:33:44:55'/>
<model type='virtio'/>
<teaming type='persistent'/>
<alias name='ua-backup0'/>
</interface>
<interface type='network'>
<source network='hostdev-pool'/>
<mac address='00:11:22:33:44:55'/>
<model type='virtio'/>
<teaming type='transient' persistent='ua-backup0'/>
</interface>
</devices>
...
The <teaming> element required
attribute type will be set to
either "persistent" to indicate a device that
should always be present in the domain,
or "transient" to indicate a device that may
periodically be removed, then later re-added to the domain. When
type="transient", there should be a second attribute
to <teaming> called "persistent"
- this attribute should be set to the alias name of the other
device in the pair (the one that has <teaming
type="persistent'/>).
In the particular case of QEMU,
libvirt's <teaming> element is used to setup
a virtio-net "failover" device pair. For this setup, the
persistent device must be an interface with <model
type="virtio"/>, and the transient device must
be <interface type='hostdev'/>
(or <interface type='network'/> where the
referenced network defines a pool of SRIOV VFs). The guest will
then have a simple network team/bond device made of the virtio
NIC + hostdev NIC pair. In this configuration, the
higher-performing hostdev NIC will normally be preferred for all
network traffic, but when the domain is migrated, QEMU will
automatically unplug the VF from the guest, and then hotplug a
similar device once migration is completed; while migration is
taking place, network traffic will use the virtio NIC. (Of
course the emulated virtio NIC and the hostdev NIC must be
connected to the same subnet for bonding to work properly).
NB1: Since you must know the alias name of the virtio NIC when configuring the hostdev NIC, it will need to be manually set in the virtio NIC's configuration (as with all other manually set alias names, this means it must start with "ua-").
NB2: Currently the only implementation of the guest OS virtio-net driver supporting virtio-net failover requires that the MAC addresses of the virtio and hostdev NIC must match. Since that may not always be a requirement in the future, libvirt doesn't enforce this limitation - it is up to the person/management application that is creating the configuration to assure the MAC addresses of the two devices match.
NB3: Since the PCI addresses of the SRIOV VFs on the hosts that
are the source and destination of the migration will almost
certainly be different, either higher level management software
will need to modify the <source> of the
hostdev NIC (<interface type='hostdev'>) at
the start of migration, or (a simpler solution) the
configuration will need to use a libvirt "hostdev" virtual
network that maintains a pool of such devices, as is implied in
the example's use of the libvirt network named "hostdev-pool" -
as long as the hostdev network pools on both hosts have the same
name, libvirt itself will take care of allocating an appropriate
device on both ends of the migration. Similarly the XML for the
virtio interface must also either work correctly unmodified on
both the source and destination of the migration (e.g. by
connecting to the same bridge device on both hosts, or by using
the same virtual network), or the management software must
properly modify the interface XML during migration so that the
virtio device remains connected to the same network segment
before and after migration.
A multicast group is setup to represent a virtual network. Any VMs whose network devices are in the same multicast group can talk to each other even across hosts. This mode is also available to unprivileged users. There is no default DNS or DHCP support and no outgoing network access. To provide outgoing network access, one of the VMs should have a 2nd NIC which is connected to one of the first 4 network types and do the appropriate routing. The multicast protocol is compatible with that used by user mode linux guests too. The source address used must be from the multicast address block.
...
<devices>
<interface type='mcast'>
<mac address='52:54:00:6d:90:01'/>
<source address='230.0.0.1' port='5558'/>
</interface>
</devices>
...
A TCP client/server architecture provides a virtual network. One VM provides the server end of the network, all other VMS are configured as clients. All network traffic is routed between the VMs via the server. This mode is also available to unprivileged users. There is no default DNS or DHCP support and no outgoing network access. To provide outgoing network access, one of the VMs should have a 2nd NIC which is connected to one of the first 4 network types and do the appropriate routing.
...
<devices>
<interface type='server'>
<mac address='52:54:00:22:c9:42'/>
<source address='192.168.0.1' port='5558'/>
</interface>
...
<interface type='client'>
<mac address='52:54:00:8b:c9:51'/>
<source address='192.168.0.1' port='5558'/>
</interface>
</devices>
...
A UDP unicast architecture provides a virtual network which enables connections between QEMU instances using QEMU's UDP infrastructure. The xml "source" address is the endpoint address to which the UDP socket packets will be sent from the host running QEMU. The xml "local" address is the address of the interface from which the UDP socket packets will originate from the QEMU host. Since 1.2.20
...
<devices>
<interface type='udp'>
<mac address='52:54:00:22:c9:42'/>
<source address='127.0.0.1' port='11115'>
<local address='127.0.0.1' port='11116'/>
</source>
</interface>
</devices>
...
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<model type='ne2k_pci'/>
</interface>
</devices>
...
For hypervisors which support this, you can set the model of emulated network interface card.
The values for type aren't defined specifically by
libvirt, but by what the underlying hypervisor supports (if
any). For QEMU and KVM you can get a list of supported models
with these commands:
qemu -net nic,model=? /dev/null qemu-kvm -net nic,model=? /dev/null
Typical values for QEMU and KVM include:
ne2k_isa i82551 i82557b i82559er ne2k_pci pcnet rtl8139 e1000 virtio.
Since 5.2.0, virtio-transitional
and virtio-non-transitional values are supported.
See Virtio transitional devices
for more details.
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<model type='virtio'/>
<driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off' queues='5' rx_queue_size='256' tx_queue_size='256'>
<host csum='off' gso='off' tso4='off' tso6='off' ecn='off' ufo='off' mrg_rxbuf='off'/>
<guest csum='off' tso4='off' tso6='off' ecn='off' ufo='off'/>
</driver>
</interface>
</devices>
...
Some NICs may have tunable driver-specific options. These are
set as attributes of the driver sub-element of the
interface definition. Currently the following attributes are
available for the "virtio" NIC driver:
namename attribute forces which type of
backend driver to use. The value can be either 'qemu' (a
user-space backend) or 'vhost' (a kernel backend, which
requires the vhost module to be provided by the kernel); an
attempt to require the vhost driver without kernel support
will be rejected. If this attribute is not present, then the
domain defaults to 'vhost' if present, but silently falls back
to 'qemu' without error.
Since 0.8.8 (QEMU and KVM only)
name attribute can optionally be set to
"vfio" or "kvm". "vfio" tells libvirt to use VFIO device
assignment rather than traditional KVM device assignment (VFIO
is a new method of device assignment that is compatible with
UEFI Secure Boot), and "kvm" tells libvirt to use the legacy
device assignment performed directly by the kvm kernel module
(the default is currently "kvm", but is subject to change).
Since 1.0.5 (QEMU and KVM only, requires
kernel 3.6 or newer)
name
attribute is ignored. The backend driver used is always
vhost-user.
txmodetxmode attribute specifies how to handle
transmission of packets when the transmit buffer is full. The
value can be either 'iothread' or 'timer'.
Since 0.8.8 (QEMU and KVM only)ioeventfdevent_idxevent_idx attribute controls some aspects of
device event processing. The value can be either 'on' or 'off'
- if it is on, it will reduce the number of interrupts and
exits for the guest. The default is determined by QEMU;
usually if the feature is supported, default is on. In case
there is a situation where this behavior is suboptimal, this
attribute provides a way to force the feature off.
Since 0.9.5 (QEMU and KVM only)queuesqueues attribute controls the number
of queues to be used for either
Multiqueue
virtio-net or vhost-user network
interfaces. Use of multiple packet processing queues requires the
interface having the <model type='virtio'/>
element. Each queue will potentially be handled by a different
processor, resulting in much higher throughput.
virtio-net since 1.0.6 (QEMU and KVM only)
vhost-user since 1.2.17 (QEMU and KVM only)
rx_queue_sizerx_queue_size attribute controls
the size of virtio ring for each queue as described above.
The default value is hypervisor dependent and may change
across its releases. Moreover, some hypervisors may pose
some restrictions on actual value. For instance, latest
QEMU (as of 2016-09-01) requires value to be a power of two
from [256, 1024] range.
Since 2.3.0 (QEMU and KVM only)tx_queue_sizetx_queue_size attribute controls
the size of virtio ring for each queue as described above.
The default value is hypervisor dependent and may change
across its releases. Moreover, some hypervisors may pose
some restrictions on actual value. For instance, QEMU
v2.9 requires value to be a power of two from [256, 1024]
range. In addition to that, this may work only for a subset of
interface types, e.g. aforementioned QEMU enables this option
only for vhostuser type.
Since 3.7.0 (QEMU and KVM only)Offloading options for the host and guest can be configured using the following sub-elements:
hostcsum, gso, tso4,
tso6, ecn and ufo
attributes with possible values on
and off can be used to turn off host offloading options.
By default, the supported offloads are enabled by QEMU.
Since 1.2.9 (QEMU only)
The mrg_rxbuf attribute can be used to control
mergeable rx buffers on the host side. Possible values are
on (default) and off.
Since 1.2.13 (QEMU only)
guestcsum, tso4,
tso6, ecn and ufo
attributes with possible values on
and off can be used to turn off guest offloading options.
By default, the supported offloads are enabled by QEMU.
Since 1.2.9 (QEMU only)
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<model type='virtio'/>
<backend tap='/dev/net/tun' vhost='/dev/vhost-net'/>
<driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off' queues='5'/>
<tune>
<sndbuf>1600</sndbuf>
</tune>
</interface>
</devices>
...
For tuning the backend of the network, the backend element
can be used. The vhost attribute can override the default vhost
device path (/dev/vhost-net) for devices with virtio model.
The tap attribute overrides the tun/tap device path (default:
/dev/net/tun) for network and bridge interfaces. This does not work
in session mode. Since 1.2.9
For tap devices there is also sndbuf element which can
adjust the size of send buffer in the host. Since
0.8.8
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
</interface>
</devices>
...
If no target is specified, certain hypervisors will automatically generate a name for the created tun device. This name can be manually specified, however the name should not start with either 'vnet', 'vif', 'macvtap', or 'macvlan', which are prefixes reserved by libvirt and certain hypervisors. Manually specified targets using these prefixes may be ignored.
Note that for LXC containers, this defines the name of the interface
on the host side. Since 1.2.7, to define
the name of the device on the guest side, the guest
element should be used, as in the following snippet:
...
<devices>
<interface type='network'>
<source network='default'/>
<guest dev='myeth'/>
</interface>
</devices>
...
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<boot order='1'/>
</interface>
</devices>
...
For hypervisors which support this, you can set a specific NIC to
be used for network boot. The order attribute determines
the order in which devices will be tried during boot sequence. The
per-device boot elements cannot be used together with
general boot elements in
BIOS bootloader section.
Since 0.8.8
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<rom bar='on' file='/etc/fake/boot.bin'/>
</interface>
</devices>
...
For hypervisors which support this, you can change how a PCI Network
device's ROM is presented to the guest. The bar
attribute can be set to "on" or "off", and determines whether
or not the device's ROM will be visible in the guest's memory
map. (In PCI documentation, the "rombar" setting controls the
presence of the Base Address Register for the ROM). If no rom
bar is specified, the qemu default will be used (older
versions of qemu used a default of "off", while newer qemus
have a default of "on").
The optional file attribute is used to point to a
binary file to be presented to the guest as the device's ROM
BIOS. This can be useful to provide an alternative boot ROM for a
network device.
Since 0.9.10 (QEMU and KVM only).
...
<devices>
...
<interface type='bridge'>
<source bridge='br0'/>
<backenddomain name='netvm'/>
</interface>
...
</devices>
...
The optional backenddomain element allows specifying a
backend domain (aka driver domain) for the interface. Use the
name attribute to specify the backend domain name. You
can use it to create a direct network link between domains (so data
will not go through host system). Use with type 'ethernet' to create
plain network link, or with type 'bridge' to connect to a bridge inside
the backend domain.
Since 1.2.13 (Xen only)
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<bandwidth>
<inbound average='1000' peak='5000' floor='200' burst='1024'/>
<outbound average='128' peak='256' burst='256'/>
</bandwidth>
</interface>
</devices>
...
This part of interface XML provides setting quality of service. Incoming
and outgoing traffic can be shaped independently.
The bandwidth element and its child elements are described
in the QoS section of
the Network XML.
...
<devices>
<interface type='bridge'>
<vlan>
<tag id='42'/>
</vlan>
<source bridge='ovsbr0'/>
<virtualport type='openvswitch'>
<parameters interfaceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/>
</virtualport>
</interface>
<interface type='bridge'>
<vlan trunk='yes'>
<tag id='42'/>
<tag id='123' nativeMode='untagged'/>
</vlan>
...
</interface>
</devices>
...
If (and only if) the network connection used by the guest
supports VLAN tagging transparent to the guest, an
optional <vlan> element can specify one or
more VLAN tags to apply to the guest's network
traffic Since 0.10.0. Network
connections that support guest-transparent VLAN tagging include
1) type='bridge' interfaces connected to an Open vSwitch bridge
Since 0.10.0, 2) SRIOV Virtual
Functions (VF) used via type='hostdev' (direct device
assignment) Since 0.10.0, and 3)
SRIOV VFs used via type='direct' with mode='passthrough'
(macvtap "passthru" mode) Since
1.3.5. All other connection types, including standard
linux bridges and libvirt's own virtual networks, do not
support it. 802.1Qbh (vn-link) and 802.1Qbg (VEPA) switches
provide their own way (outside of libvirt) to tag guest traffic
onto a specific VLAN. Each tag is given in a
separate <tag> subelement
of <vlan> (for example: <tag
id='42'/>). For VLAN trunking of multiple tags (which
is supported only on Open vSwitch connections),
multiple <tag> subelements can be specified,
which implies that the user wants to do VLAN trunking on the
interface for all the specified tags. In the case that VLAN
trunking of a single tag is desired, the optional
attribute trunk='yes' can be added to the toplevel
<vlan> element to differentiate trunking of a
single tag from normal tagging.
For network connections using Open vSwitch it is also possible
to configure 'native-tagged' and 'native-untagged' VLAN modes
Since 1.1.0. This is done with the
optional nativeMode attribute on
the <tag> subelement: nativeMode
may be set to 'tagged' or 'untagged'. The id
attribute of the <tag> subelement
containing nativeMode sets which VLAN is considered
to be the "native" VLAN for this interface, and
the nativeMode attribute determines whether or not
traffic for that VLAN will be tagged.
...
<devices>
<interface type='network'>
<source network='default'/>
<port isolated='yes'/>
</interface>
</devices>
...
Since 6.1.0. The port
element property isolated, when set
to yes (default setting is no) is used
to isolate this interface's network traffic from that of other
guest interfaces connected to the same network that also
have <port isolated='yes'/>. This setting is
only supported for emulated interface devices that use a
standard tap device to connect to the network via a Linux host
bridge. This property can be inherited from a libvirt network,
so if all guests that will be connected to the network should be
isolated, it is better to put the setting in the network
configuration. (NB: this only prevents guests that
have isolated='yes' from communicating with each
other; if there is a guest on the same bridge that doesn't
have isolated='yes', even the isolated guests will
be able to communicate with it.)
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<link state='down'/>
</interface>
</devices>
...
This element provides means of setting state of the virtual network link.
Possible values for attribute state are up and
down. If down is specified as the value, the interface
behaves as if it had the network cable disconnected. Default behavior if this
element is unspecified is to have the link state up.
Since 0.9.5
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<mtu size='1500'/>
</interface>
</devices>
...
This element provides means of setting MTU of the virtual network link.
Currently there is just one attribute size which accepts a
non-negative integer which specifies the MTU size for the interface.
Since 3.1.0
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<coalesce>
<rx>
<frames max='7'/>
</rx>
</coalesce>
</interface>
</devices>
...
This element provides means of setting coalesce settings for
some interface devices (currently only type network
and bridge. Currently there is just one attribute,
max, to tweak, in element frames for
the rx group, which accepts a non-negative integer
that specifies the maximum number of packets that will be
received before an interrupt.
Since 3.3.0
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<ip address='192.168.122.5' prefix='24'/>
<ip address='192.168.122.5' prefix='24' peer='10.0.0.10'/>
<route family='ipv4' address='192.168.122.0' prefix='24' gateway='192.168.122.1'/>
<route family='ipv4' address='192.168.122.8' gateway='192.168.122.1'/>
</interface>
...
<hostdev mode='capabilities' type='net'>
<source>
<interface>eth0</interface>
</source>
<ip address='192.168.122.6' prefix='24'/>
<route family='ipv4' address='192.168.122.0' prefix='24' gateway='192.168.122.1'/>
<route family='ipv4' address='192.168.122.8' gateway='192.168.122.1'/>
</hostdev>
...
</devices>
...
Since 1.2.12 network devices and
hostdev devices with network capabilities can optionally be provided
one or more IP addresses to set on the network device in the
guest. Note that some hypervisors or network device types will
simply ignore them or only use the first one.
The family attribute can be set to
either ipv4 or ipv6, and the
address attribute contains the IP address. The
optional prefix is the number of 1 bits in the
netmask, and will be automatically set if not specified - for
IPv4 the default prefix is determined according to the network
"class" (A, B, or C - see RFC870), and for IPv6 the default
prefix is 64. The optional peer attribute holds the
IP address of the other end of a point-to-point network
device (since 2.1.0).
Since 1.2.12 route elements can also be
added to define IP routes to add in the guest. The attributes of
this element are described in the documentation for
the route element
in network
definitions. This is used by the LXC driver.
...
<devices>
<interface type='ethernet'>
<source/>
<ip address='192.168.123.1' prefix='24'/>
<ip address='10.0.0.10' prefix='24' peer='192.168.122.5'/>
<route family='ipv4' address='192.168.42.0' prefix='24' gateway='192.168.123.4'/>
<source/>
...
</interface>
...
</devices>
...
Since 2.1.0 network devices of type
"ethernet" can optionally be provided one or more IP addresses
and one or more routes to set on the host side of the
network device. These are configured as subelements of
the <source> element of the interface, and
have the same attributes as the similarly named elements used to
configure the guest side of the interface (described above).
Since 1.2.7 the vhost-user enables the communication between a QEMU virtual machine and other userspace process using the Virtio transport protocol. A char dev (e.g. Unix socket) is used for the control plane, while the data plane is based on shared memory.
...
<devices>
<interface type='vhostuser'>
<mac address='52:54:00:3b:83:1a'/>
<source type='unix' path='/tmp/vhost1.sock' mode='server'/>
<model type='virtio'/>
</interface>
<interface type='vhostuser'>
<mac address='52:54:00:3b:83:1b'/>
<source type='unix' path='/tmp/vhost2.sock' mode='client'>
<reconnect enabled='yes' timeout='10'/>
</source>
<model type='virtio'/>
<driver queues='5'/>
</interface>
</devices>
...
The <source> element has to be specified
along with the type of char device.
Currently, only type='unix' is supported, where the path (the
directory path of the socket) and mode attributes are required.
Both mode='server' and mode='client'
are supported.
vhost-user requires the virtio model type, thus the
<model> element is mandatory.
Since 4.1.0 the element has an
optional child element reconnect which
configures reconnect timeout if the connection is lost. It
has two attributes enabled (which accepts
yes and no) and
timeout which specifies the amount of seconds
after which hypervisor tries to reconnect.
Since 0.8.0 an nwfilter profile
can be assigned to a domain interface, which allows configuring
traffic filter rules for the virtual machine.
See the nwfilter documentation for more
complete details.
...
<devices>
<interface ...>
...
<filterref filter='clean-traffic'/>
</interface>
<interface ...>
...
<filterref filter='myfilter'>
<parameter name='IP' value='104.207.129.11'/>
<parameter name='IP6_ADDR' value='2001:19f0:300:2102::'/>
<parameter name='IP6_MASK' value='64'/>
...
</filterref>
</interface>
</devices>
...
The filter attribute specifies the name of the nwfilter
to use. Optional <parameter> elements may be
specified for passing additional info to the nwfilter via the
name and value attributes. See
the nwfilter
docs for info on parameters.
Input devices allow interaction with the graphical framebuffer in the guest virtual machine. When enabling the framebuffer, an input device is automatically provided. It may be possible to add additional devices explicitly, for example, to provide a graphics tablet for absolute cursor movement.
...
<devices>
<input type='mouse' bus='usb'/>
<input type='keyboard' bus='usb'/>
<input type='mouse' bus='virtio'/>
<input type='keyboard' bus='virtio'/>
<input type='tablet' bus='virtio'/>
<input type='passthrough' bus='virtio'>
<source evdev='/dev/input/event1/>
</input>
</devices>
...
inputinput element has one mandatory attribute,
the type whose value can be 'mouse', 'tablet',
(since 1.2.2) 'keyboard' or
(since 1.3.0) 'passthrough'.
The tablet provides absolute cursor movement,
while the mouse uses relative movement. The optional
bus attribute can be used to refine the exact device type.
It takes values "xen" (paravirtualized), "ps2" and "usb" or
(since 1.3.0) "virtio".
The input element has an optional
sub-element <address> which can tie the
device to a particular PCI
slot, documented above.
On S390, address can be used to provide a CCW address for
an input device (since 4.2.0).
For type passthrough, the mandatory sub-element source
must have an evdev attribute containing the absolute path to the
event device passed through to guests. (KVM only)
Since 5.2.0, the input element
accepts a model attribute which has the values 'virtio',
'virtio-transitional' and 'virtio-non-transitional'. See
Virtio transitional devices
for more details.
The subelement driver can be used to tune the virtio
options of the device:
Virtio-specific options can also be
set. (Since 3.5.0)
A hub is a device that expands a single port into several so that there are more ports available to connect devices to a host system.
... <devices> <hub type='usb'/> </devices> ...
hubhub element has one mandatory attribute,
the type whose value can only be 'usb'.
The hub element has an optional
sub-element <address>
with type='usb'which can tie the device to a
particular controller, documented
above.
A graphics device allows for graphical interaction with the guest OS. A guest will typically have either a framebuffer or a text console configured to allow interaction with the admin.
...
<devices>
<graphics type='sdl' display=':0.0'/>
<graphics type='vnc' port='5904' sharePolicy='allow-exclusive'>
<listen type='address' address='1.2.3.4'/>
</graphics>
<graphics type='rdp' autoport='yes' multiUser='yes' />
<graphics type='desktop' fullscreen='yes'/>
<graphics type='spice'>
<listen type='network' network='rednet'/>
</graphics>
</devices>
...
graphics
The graphics element has a mandatory type
attribute which takes the value sdl, vnc,
spice, rdp, desktop or
egl-headless:
sdl
This displays a window on the host desktop, it can take 3 optional
arguments: a display attribute for the display to use,
an xauth attribute for the authentication identifier,
and an optional fullscreen attribute accepting values
yes or no.
You can use a gl with the enable="yes"
property to enable OpenGL support in SDL. Likewise you can
explicitly disable OpenGL support with enable="no".
vnc
Starts a VNC server. The port attribute specifies
the TCP port number (with -1 as legacy syntax indicating that it
should be auto-allocated). The autoport attribute is
the new preferred syntax for indicating auto-allocation of the TCP
port to use. The passwd attribute provides a VNC
password in clear text. If the passwd attribute is
set to an empty string, then VNC access is disabled. The
keymap attribute specifies the keymap to use. It is
possible to set a limit on the validity of the password by giving
a timestamp passwdValidTo='2010-04-09T15:51:00'
assumed to be in UTC. The connected attribute allows
control of connected client during password changes. VNC accepts
keep value only since 0.9.3.
NB, this may not be supported by all hypervisors.
The optional sharePolicy attribute specifies vnc
server display sharing policy. allow-exclusive allows
clients to ask for exclusive access by dropping other connections.
Connecting multiple clients in parallel requires all clients asking
for a shared session (vncviewer: -Shared switch). This is
the default value. force-shared disables exclusive
client access, every connection has to specify -Shared switch for
vncviewer. ignore welcomes every connection
unconditionally since 1.0.6.
Rather than using listen/port, QEMU supports a socket
attribute for listening on a unix domain socket path
Since 0.8.8.
For VNC WebSocket functionality, websocket attribute
may be used to specify port to listen on (with -1 meaning
auto-allocation and autoport having no effect due to
security reasons) Since 1.0.6.
Although VNC doesn't support OpenGL natively, it can be paired
with graphics type egl-headless (see below) which
will instruct QEMU to open and use drm nodes for OpenGL rendering.
spice Since 0.8.6
Starts a SPICE server. The port attribute specifies
the TCP port number (with -1 as legacy syntax indicating that it
should be auto-allocated), while tlsPort gives
an alternative secure port number. The autoport
attribute is the new preferred syntax for indicating
auto-allocation of needed port numbers. The passwd
attribute provides a SPICE password in clear text. If the
passwd attribute is set to an empty string, then
SPICE access is disabled. The keymap attribute
specifies the keymap to use. It is possible to set a limit on
the validity of the password by giving a timestamp
passwdValidTo='2010-04-09T15:51:00' assumed to be
in UTC.
The connected attribute allows control of connected
client during password changes. SPICE accepts keep to
keep client connected, disconnect to disconnect client
and fail to fail changing password . NB, this may not
be supported by all hypervisors.
Since 0.9.3
The defaultMode attribute sets the default channel
security policy, valid values are secure,
insecure and the default any (which is
secure if possible, but falls back to insecure rather than erroring
out if no secure path is available).
Since 0.9.12
When SPICE has both a normal and TLS secured TCP port configured,
it can be desirable to restrict what channels can be run on each
port. This is achieved by adding one or more <channel>
elements inside the main <graphics>
element and setting the mode attribute to either
secure or insecure. Setting the mode
attribute overrides the default value as set by
the defaultMode attribute. (Note that specifying
any as mode discards the entry as the channel would
inherit the default mode anyways.) Valid channel names include
main, display, inputs,
cursor, playback, record
(all since 0.8.6);
smartcard (since 0.8.8);
and usbredir (since 0.9.12).
<graphics type='spice' port='-1' tlsPort='-1' autoport='yes'> <channel name='main' mode='secure'/> <channel name='record' mode='insecure'/> <image compression='auto_glz'/> <streaming mode='filter'/> <clipboard copypaste='no'/> <mouse mode='client'/> <filetransfer enable='no'/> <gl enable='yes' rendernode='/dev/dri/by-path/pci-0000:00:02.0-render'/> </graphics>
Spice supports variable compression settings for audio, images and
streaming. These settings are accessible via the compression
attribute in all following elements: image to
set image compression (accepts auto_glz,
auto_lz, quic, glz,
lz, off), jpeg for JPEG
compression for images over wan (accepts auto,
never, always), zlib for
configuring wan image compression (accepts auto,
never, always) and playback
for enabling audio stream compression (accepts on or
off). Since 0.9.1
Streaming mode is set by the streaming element,
settings its mode attribute to one of
filter, all or off.
Since 0.9.2
Copy & Paste functionality (via Spice agent) is set by the
clipboard element. It is enabled by default, and can
be disabled by setting the copypaste property to
no. Since 0.9.3
Mouse mode is set by the mouse element, setting its
mode attribute to one of server or
client. If no mode is specified, the qemu default will
be used (client mode). Since 0.9.11
File transfer functionality (via Spice agent) is set using the
filetransfer element. It is enabled by default, and
can be disabled by setting the enable property to
no. Since 1.2.2
Spice may provide accelerated server-side rendering with OpenGL.
You can enable or disable OpenGL support explicitly with
the gl element, by setting the enable
property. (QEMU only, since 1.3.3).
Note that this only works locally, since this requires usage of
UNIX sockets, i.e. using listen types 'socket' or
'none'. For accelerated OpenGL with remote support, consider
pairing this element with type egl-headless
(see below). However, this will deliver weaker performance
compared to native Spice OpenGL support.
By default, QEMU will pick the first available GPU DRM render node. You may specify a DRM render node path to use instead. (QEMU only, since 3.1.0).
rdp
Starts a RDP server. The port attribute specifies the
TCP port number (with -1 as legacy syntax indicating that it should
be auto-allocated). The autoport attribute is the new
preferred syntax for indicating auto-allocation of the TCP port to
use. In the VirtualBox driver, the autoport will make
the hypervisor pick available port from 3389-3689 range when the VM
is started. The chosen port will be reflected in the port
attribute. The multiUser attribute is a boolean deciding
whether multiple simultaneous connections to the VM are permitted.
The replaceUser attribute is a boolean deciding whether
the existing connection must be dropped and a new connection must
be established by the VRDP server, when a new client connects in
single connection mode.
desktop
This value is reserved for VirtualBox domains for the moment. It
displays a window on the host desktop, similarly to "sdl", but
using the VirtualBox viewer. Just like "sdl", it accepts
the optional attributes display and
fullscreen.
egl-headlessSince 4.6.0
This display type provides support for an OpenGL accelerated
display accessible both locally and remotely (for comparison,
Spice's native OpenGL support only works locally using UNIX
sockets at the moment, but has better performance). Since this
display type doesn't provide any window or graphical console like
the other types, for practical reasons it should be paired with
either vnc or spice graphics types.
This display type is only supported by QEMU domains
(needs QEMU 2.10 or newer).
5.0.0 this element accepts a
<gl/> sub-element with an optional attribute
rendernode which can be used to specify an absolute
path to a host's DRI device to be used for OpenGL rendering.
<graphics type='spice' autoport='yes'/>
<graphics type='egl-headless'>
<gl rendernode='/dev/dri/renderD128'/>
</graphics>
Graphics device uses a <listen> to set up where
the device should listen for clients. It has a mandatory attribute
type which specifies the listen type. Only vnc,
spice and rdp supports <listen>
element. Since 0.9.4.
Available types are:
address
Tells a graphics device to use an address specified in the
address attribute, which will contain either an IP address
or hostname (which will be resolved to an IP address via a DNS query)
to listen on.
It is possible to omit the address attribute in order to
use an address from config files Since 1.3.5.
The address attribute is duplicated as listen
attribute in graphics element for backward compatibility.
If both are provided they must be equal.
network
This is used to specify an existing network in the network
attribute from libvirt's list of configured networks. The named network
configuration will be examined to determine an appropriate listen
address and the address will be stored in live XML in address
attribute. For example, if the network has an IPv4 address in
its configuration (e.g. if it has a forward type of route,
nat, or no forward type (isolated)), the first IPv4
address listed in the network's configuration will be used.
If the network is describing a host bridge, the first IPv4 address
associated with that bridge device will be used, and if the network is
describing one of the 'direct' (macvtap) modes, the first IPv4 address
of the first forward dev will be used.
socket since 2.0.0 (QEMU only)
This listen type tells a graphics server to listen on unix socket.
Attribute socket contains a path to unix socket. If this
attribute is omitted libvirt will generate this path for you.
Supported by graphics type vnc and spice.
For vnc graphics be backward compatible
the socket attribute of first listen element
is duplicated as socket attribute in graphics
element. If graphics element contains a socket
attribute all listen elements are ignored.
none since 2.0.0 (QEMU only)
This listen type doesn't have any other attribute. Libvirt supports
passing a file descriptor through our APIs virDomainOpenGraphics() and
virDomainOpenGraphicsFD(). No other listen types are allowed if this
one is used and the graphics device doesn't listen anywhere. You need
to use one of the two APIs to pass a FD to QEMU in order to connect to
this graphics device. Supported by graphics type vnc and
spice.
A video device.
...
<devices>
<video>
<model type='vga' vram='16384' heads='1'>
<acceleration accel3d='yes' accel2d='yes'/>
</model>
<driver name='qemu'/>
</video>
</devices>
...
video
The video element is the container for describing
video devices. For backwards compatibility, if no video
is set but there is a graphics in domain xml, then
libvirt will add a default video according to the guest
type.
For a guest of type "kvm", the default video is:
type with value "cirrus", vram with value
"16384" and heads with value "1". By default, the first
video device in domain xml is the primary one, but the optional
attribute primary (since 1.0.2)
with value 'yes' can be used to mark the primary in cases of multiple
video device. The non-primary must be type of "qxl" or
(since 2.4.0) "virtio".
model
The model element has a mandatory type
attribute which takes the value "vga", "cirrus", "vmvga", "xen",
"vbox", "qxl" (since 0.8.6),
"virtio" (since 1.3.0),
"gop" (since 3.2.0),
"bochs" (since 5.6.0), "ramfb"
(since 5.9.0), or "none"
(since 4.6.0, depending on the hypervisor
features available.
The purpose of the type none is to instruct libvirt not
to add a default video device in the guest (see the paragraph above).
This legacy behaviour can be inconvenient in cases where GPU mediated
devices are meant to be the only rendering device within a guest and
so specifying another video device along with type
none.
Refer to Host device assignment to see
how to add a mediated device into a guest.
You can provide the amount of video memory in kibibytes (blocks of
1024 bytes) using vram. This is supported only for guest
type of "libxl", "vz", "qemu", "vbox", "vmx" and "xen". If no
value is provided the default is used. If the size is not a power of
two it will be rounded to closest one.
The number of screen can be set using heads. This is
supported only for guests type of "vz", "kvm", "vbox" and "vmx".
For guest type of "kvm" or "qemu" and model type "qxl" there are
optional attributes. Attribute ram (
since 1.0.2) specifies the size of the primary bar, while the
attribute vram specifies the secondary bar size.
If ram or vram are not supplied a default
value is used. The ram should also be rounded to power of
two as vram. There is also optional attribute
vgamem (since 1.2.11) to set
the size of VGA framebuffer for fallback mode of QXL device.
Attribute vram64 (since 1.3.3)
extends secondary bar and makes it addressable as 64bit memory.
Since 5.9.0, the model
element may also have an optional resolution sub-element.
The resolution element has attributes x and
y to set the minimum resolution for the video device. This
sub-element is valid for model types "vga", "qxl", "bochs", and
"virtio".
accelerationaccel2daccel3drendernodeaddressaddress sub-element can be used to
tie the video device to a particular PCI slot.
On S390, address can be used to provide the
CCW address for the video device (
since 4.2.0).
driverdriver can be used to tune the device:
namevirtio
device).
vgaconf attribute which takes the value "io", "on" or "off".
At present, it's only applicable to the bhyve's "gop" video model type
(Since 3.5.0)
A character device provides a way to interact with the virtual machine. Paravirtualized consoles, serial ports, parallel ports and channels are all classed as character devices and so represented using the same syntax.
...
<devices>
<parallel type='pty'>
<source path='/dev/pts/2'/>
<target port='0'/>
</parallel>
<serial type='pty'>
<source path='/dev/pts/3'/>
<target port='0'/>
</serial>
<serial type='file'>
<source path='/tmp/file' append='on'>
<seclabel model='dac' relabel='no'/>
</source>
<target port='0'/>
</serial>
<console type='pty'>
<source path='/dev/pts/4'/>
<target port='0'/>
</console>
<channel type='unix'>
<source mode='bind' path='/tmp/guestfwd'/>
<target type='guestfwd' address='10.0.2.1' port='4600'/>
</channel>
</devices>
...
In each of these directives, the top-level element name (parallel, serial,
console, channel) describes how the device is presented to the guest. The
guest interface is configured by the target element.
The interface presented to the host is given in the type
attribute of the top-level element. The host interface is
configured by the source element.
The source element may contain an optional
seclabel to override the way that labelling
is done on the socket path. If this element is not present,
the security label is inherited from
the per-domain setting.
If the interface type presented to the host is "file",
then the source element may contain an optional attribute
append that specifies whether or not the information in
the file should be preserved on domain restart. Allowed values are
"on" and "off" (default). Since 1.3.1.
Regardless of the type, character devices can
have an optional log file associated with them. This is
expressed via a log sub-element, with a
file attribute. There can also be an append
attribute which takes the same values described above.
Since 1.3.3.
... <log file="/var/log/libvirt/qemu/guestname-serial0.log" append="off"/> ...
Each character device element has an optional
sub-element <address> which can tie the
device to a
particular controller or PCI
slot.
For character device with type unix or tcp
the source has an optional element reconnect
which configures reconnect timeout if the connection is lost.
There are two attributes, enabled where possible
values are "yes" and "no" and timeout which is in
seconds. The reconnect attribute is valid only
for connect mode.
Since 3.7.0 (QEMU driver only).
A character device presents itself to the guest as one of the following types.
...
<devices>
<parallel type='pty'>
<source path='/dev/pts/2'/>
<target port='0'/>
</parallel>
</devices>
...
target can have a port attribute, which
specifies the port number. Ports are numbered starting from 0. There are
usually 0, 1 or 2 parallel ports.
...
<devices>
<!-- Serial port -->
<serial type='pty'>
<source path='/dev/pts/3'/>
<target port='0'/>
</serial>
</devices>
...
...
<devices>
<!-- USB serial port -->
<serial type='pty'>
<target type='usb-serial' port='0'>
<model name='usb-serial'/>
</target>
<address type='usb' bus='0' port='1'/>
</serial>
</devices>
...
The target element can have an optional port
attribute, which specifies the port number (starting from 0), and an
optional type attribute: valid values are,
since 1.0.2, isa-serial (usable
with x86 guests), usb-serial (usable whenever USB support
is available) and pci-serial (usable whenever PCI support
is available); since 3.10.0,
spapr-vio-serial (usable with ppc64/pseries guests),
system-serial (usable with aarch64/virt and,
since 4.7.0, riscv/virt guests) and
sclp-serial (usable with s390 and s390x guests) are
available as well.
Since 3.10.0, the target
element can have an optional model subelement;
valid values for its name attribute are:
isa-serial (usable with the isa-serial target
type); usb-serial (usable with the usb-serial
target type); pci-serial
(usable with the pci-serial target type);
spapr-vty (usable with the spapr-vio-serial
target type); pl011 and,
since 4.7.0, 16550a (usable
with the system-serial target type);
sclpconsole and sclplmconsole (usable with
the sclp-serial target type). Providing a target model is
usually unnecessary: libvirt will automatically pick one that's suitable
for the chosen target type, and overriding that value is generally not
recommended.
If any of the attributes is not specified by the user, libvirt will choose a value suitable for most users.
Most target types support configuring the guest-visible device
address as documented above; more
specifically, acceptable address types are isa (for
isa-serial), usb (for usb-serial),
pci (for pci-serial) and spapr-vio
(for spapr-vio-serial). The system-serial
and sclp-serial target types don't support specifying an
address.
For the relationship between serial ports and consoles, see below.
...
<devices>
<!-- Serial console -->
<console type='pty'>
<source path='/dev/pts/2'/>
<target type='serial' port='0'/>
</console>
</devices>
...
...
<devices>
<!-- KVM virtio console -->
<console type='pty'>
<source path='/dev/pts/5'/>
<target type='virtio' port='0'/>
</console>
</devices>
...
The console element is used to represent interactive
serial consoles. Depending on the type of guest in use and the specifics
of the configuration, the console element might represent
the same device as an existing serial element or a separate
device.
A target subelement is supported and works the same
way as with the serial element
(see above for details).
Valid values for the type attribute are:
serial (described below);
virtio (usable whenever VirtIO support is available);
xen, lxc and openvz
(available when the corresponding hypervisor is in use).
sclp and sclplm (usable for s390 and
s390x QEMU guests) are supported for compatibility reasons but should
not be used for new guests: use the sclpconsole and
sclplmconsole target models, respectively, with the
serial element instead.
Of the target types listed above, serial is special in
that it doesn't represents a separate device, but rather the same
device as the first serial element. Due to this, there can
only be a single console element with target type
serial per guest.
Virtio consoles are usually accessible as /dev/hvc[0-7]
from inside the guest; for more information, see
http://fedoraproject.org/wiki/Features/VirtioSerial.
Since 0.8.3
For the relationship between serial ports and consoles, see below.
Due to hystorical reasons, the serial and
console elements have partially overlapping scopes.
In general, both elements are used to configure one or more serial
consoles to be used for interacting with the guest. The main difference
between the two is that serial is used for emulated,
usually native, serial consoles, whereas console is used
for paravirtualized ones.
Both emulated and paravirtualized serial consoles have advantages and disadvantages:
A configuration such as:
...
<devices>
<console type='pty'>
<target type='serial'/>
</console>
<console type='pty'>
<target type='virtio'/>
</console>
</devices>
...
will work on any platform and will result in one emulated serial console
for early boot logging / interactive / recovery use, and one
paravirtualized serial console to be used eg. as a side channel. Most
people will be fine with having just the first console
element in their configuration, but if a specific configuration is
desired then both elements should be specified.
Note that, due to the compatibility concerns mentioned earlier, all the following configurations:
... <devices> <serial type='pty'/> </devices> ...
... <devices> <console type='pty'/> </devices> ...
... <devices> <serial type='pty'/> <console type='pty'/> </devices> ...
will be treated the same and will result in a single emulated serial console being available to the guest.
This represents a private communication channel between the host and the guest.
...
<devices>
<channel type='unix'>
<source mode='bind' path='/tmp/guestfwd'/>
<target type='guestfwd' address='10.0.2.1' port='4600'/>
</channel>
<!-- KVM virtio channel -->
<channel type='pty'>
<target type='virtio' name='arbitrary.virtio.serial.port.name'/>
</channel>
<channel type='unix'>
<source mode='bind' path='/var/lib/libvirt/qemu/f16x86_64.agent'/>
<target type='virtio' name='org.qemu.guest_agent.0' state='connected'/>
</channel>
<channel type='spicevmc'>
<target type='virtio' name='com.redhat.spice.0'/>
</channel>
</devices>
...
This can be implemented in a variety of ways. The specific type of
channel is given in the type attribute of the
target element. Different channel types have different
target attributes.
guestfwdtarget
element must have address and port attributes.
Since 0.7.3virtioname is specified,
/dev/virtio-ports/$name (for more info, please see
http://fedoraproject.org/wiki/Features/VirtioSerial). The
optional element address can tie the channel to a
particular type='virtio-serial'
controller, documented above.
With qemu, if name is "org.qemu.guest_agent.0",
then libvirt can interact with a guest agent installed in the
guest, for actions such as guest shutdown or file system quiescing.
Since 0.7.7, guest agent interaction
since 0.9.10 Moreover, since 1.0.6
it is possible to have source path auto generated for virtio unix channels.
This is very useful in case of a qemu guest agent, where users don't
usually care about the source path since it's libvirt who talks to
the guest agent. In case users want to utilize this feature, they should
leave <source> element out. Since
1.2.11 the active XML for a virtio channel may contain an optional
state attribute that reflects whether a process in the
guest is active on the channel. This is an output-only attribute.
Possible values for the state attribute are
connected and disconnected.
xenstate attribute is not supported since Xen channels
lack the necessary probing mechanism.
Since 2.3.0
spicevmcmain channel. The target
element must be present, with
attribute type='virtio'; an optional
attribute name controls how the guest will have
access to the channel, and defaults
to name='com.redhat.spice.0'. The
optional address element can tie the channel to a
particular type='virtio-serial' controller.
Since 0.8.8A character device presents itself to the host as one of the following types.
This disables all input on the character device, and sends output into the virtual machine's logfile
...
<devices>
<console type='stdio'>
<target port='1'/>
</console>
</devices>
...
A file is opened and all data sent to the character device is written to the file.
...
<devices>
<serial type="file">
<source path="/var/log/vm/vm-serial.log"/>
<target port="1"/>
</serial>
</devices>
...
Connects the character device to the graphical framebuffer in a virtual console. This is typically accessed via a special hotkey sequence such as "ctrl+alt+3"
...
<devices>
<serial type='vc'>
<target port="1"/>
</serial>
</devices>
...
Connects the character device to the void. No data is ever provided to the input. All data written is discarded.
...
<devices>
<serial type='null'>
<target port="1"/>
</serial>
</devices>
...
A Pseudo TTY is allocated using /dev/ptmx. A suitable client such as 'virsh console' can connect to interact with the serial port locally.
...
<devices>
<serial type="pty">
<source path="/dev/pts/3"/>
<target port="1"/>
</serial>
</devices>
...
NB special case if <console type='pty'>, then the TTY path is also duplicated as an attribute tty='/dev/pts/3' on the top level <console> tag. This provides compat with existing syntax for <console> tags.
The character device is passed through to the underlying physical character device. The device types must match, eg the emulated serial port should only be connected to a host serial port - don't connect a serial port to a parallel port.
...
<devices>
<serial type="dev">
<source path="/dev/ttyS0"/>
<target port="1"/>
</serial>
</devices>
...
The character device writes output to a named pipe. See pipe(7) for more info.
...
<devices>
<serial type="pipe">
<source path="/tmp/mypipe"/>
<target port="1"/>
</serial>
</devices>
...
The character device acts as a TCP client connecting to a remote server.
...
<devices>
<serial type="tcp">
<source mode="connect" host="0.0.0.0" service="2445"/>
<protocol type="raw"/>
<target port="1"/>
</serial>
</devices>
...
Or as a TCP server waiting for a client connection.
...
<devices>
<serial type="tcp">
<source mode="bind" host="127.0.0.1" service="2445"/>
<protocol type="raw"/>
<target port="1"/>
</serial>
</devices>
...
Alternatively you can use telnet instead
of raw TCP in order to utilize the telnet protocol
for the connection.
Since 0.8.5, some hypervisors support
use of either telnets (secure telnet) or tls
(via secure sockets layer) as the transport protocol for connections.
...
<devices>
<serial type="tcp">
<source mode="connect" host="0.0.0.0" service="2445"/>
<protocol type="telnet"/>
<target port="1"/>
</serial>
...
<serial type="tcp">
<source mode="bind" host="127.0.0.1" service="2445"/>
<protocol type="telnet"/>
<target port="1"/>
</serial>
</devices>
...
Since 2.4.0, the optional attribute
tls can be used to control whether a chardev
TCP communication channel would utilize a hypervisor configured
TLS X.509 certificate environment in order to encrypt the data
channel. For the QEMU hypervisor, usage of a TLS environment can
be controlled on the host by the chardev_tls and
chardev_tls_x509_cert_dir or
default_tls_x509_cert_dir settings in the file
/etc/libvirt/qemu.conf. If chardev_tls is enabled,
then unless the tls attribute is set to "no", libvirt
will use the host configured TLS environment.
If chardev_tls is disabled, but the tls
attribute is set to "yes", then libvirt will attempt to use the
host TLS environment if either the chardev_tls_x509_cert_dir
or default_tls_x509_cert_dir TLS directory structure exists.
...
<devices>
<serial type="tcp">
<source mode='connect' host="127.0.0.1" service="5555" tls="yes"/>
<protocol type="raw"/>
<target port="0"/>
</serial>
</devices>
...
The character device acts as a UDP netconsole service, sending and receiving packets. This is a lossy service.
...
<devices>
<serial type="udp">
<source mode="bind" host="0.0.0.0" service="2445"/>
<source mode="connect" host="0.0.0.0" service="2445"/>
<target port="1"/>
</serial>
</devices>
...
The character device acts as a UNIX domain socket server, accepting connections from local clients.
...
<devices>
<serial type="unix">
<source mode="bind" path="/tmp/foo"/>
<target port="1"/>
</serial>
</devices>
...
The character device is accessible through spice connection
under a channel name specified in the channel
attribute. Since 1.2.2
Note: depending on the hypervisor, spiceports might (or might not) be enabled on domains with or without spice graphics.
...
<devices>
<serial type="spiceport">
<source channel="org.qemu.console.serial.0"/>
<target port="1"/>
</serial>
</devices>
...
The nmdm device driver, available on FreeBSD, provides two tty devices connected together by a virtual null modem cable. Since 1.2.4
...
<devices>
<serial type="nmdm">
<source master="/dev/nmdm0A" slave="/dev/nmdm0B"/>
</serial>
</devices>
...
The source element has these attributes:
masterslave
A virtual sound card can be attached to the host via the
sound element. Since 0.4.3
... <devices> <sound model='es1370'/> </devices> ...
soundsound element has one mandatory attribute,
model, which specifies what real sound device is emulated.
Valid values are specific to the underlying hypervisor, though typical
choices are 'es1370', 'sb16', 'ac97', 'ich6' and 'usb'.
(
'ac97' only since 0.6.0, 'ich6' only since 0.8.8,
'usb' only since 1.2.7)
Since 0.9.13, a sound element
with ich6 model can have optional
sub-elements <codec> to attach various audio
codecs to the audio device. If not specified, a default codec
will be attached to allow playback and recording.
Valid values are:
...
<devices>
<sound model='ich6'>
<codec type='micro'/>
</sound>
</devices>
...
Each sound element has an optional
sub-element <address> which can tie the
device to a particular PCI
slot, documented above.
A virtual hardware watchdog device can be added to the guest via
the watchdog element.
Since 0.7.3, QEMU and KVM only
The watchdog device requires an additional driver and management daemon in the guest. Just enabling the watchdog in the libvirt configuration does not do anything useful on its own.
Currently libvirt does not support notification when the watchdog fires. This feature is planned for a future version of libvirt.
... <devices> <watchdog model='i6300esb'/> </devices> ...
...
<devices>
<watchdog model='i6300esb' action='poweroff'/>
</devices>
</domain>
model
The required model attribute specifies what real
watchdog device is emulated. Valid values are specific to the
underlying hypervisor.
QEMU and KVM support:
action
The optional action attribute describes what
action to take when the watchdog expires. Valid values are
specific to the underlying hypervisor.
QEMU and KVM support:
Note 1: the 'shutdown' action requires that the guest is responsive to ACPI signals. In the sort of situations where the watchdog has expired, guests are usually unable to respond to ACPI signals. Therefore using 'shutdown' is not recommended.
Note 2: the directory to save dump files can be configured
by auto_dump_path in file /etc/libvirt/qemu.conf.
A virtual memory balloon device is added to all Xen and KVM/QEMU
guests. It will be seen as memballoon element.
It will be automatically added when appropriate, so there is no
need to explicitly add this element in the guest XML unless a
specific PCI slot needs to be assigned.
Since 0.8.3, Xen, QEMU and KVM only
Additionally, since 0.8.4, if the
memballoon device needs to be explicitly disabled,
model='none' may be used.
Example: automatically added device with KVM
... <devices> <memballoon model='virtio'/> </devices> ...
Example: manually added device with static PCI slot 2 requested
...
<devices>
<memballoon model='virtio'>
<address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
<stats period='10'/>
<driver iommu='on' ats='on'/>
</memballoon>
</devices>
</domain>
model
The required model attribute specifies what type
of balloon device is provided. Valid values are specific to
the virtualization platform
autodeflate
The optional autodeflate attribute allows to
enable/disable (values "on"/"off", respectively) the ability of the
QEMU virtio memory balloon to release some memory at the last moment
before a guest's process get killed by Out of Memory killer.
Since 1.3.1, QEMU and KVM only
period
The optional period allows the QEMU virtio memory balloon
driver to provide statistics through the virsh dommemstat
[domain] command. By default, collection is not enabled. In
order to enable, use the virsh dommemstat [domain] --period
[number] command or virsh edit command to add the
option to the XML definition. The virsh dommemstat will
accept the options --live, --current,
or --config. If an option is not provided, the change
for a running domain will only be made to the active guest. If the
QEMU driver is not at the right revision, the attempt to set the
period will fail. Large values (e.g. many years) might be ignored.
Since 1.1.1, requires QEMU 1.5
drivervirtio memballoon,
Virtio-specific options can also be
set. (Since 3.5.0)
The virtual random number generator device allows the host to pass through entropy to guest operating systems. Since 1.0.3
Example: usage of the RNG device:
...
<devices>
<rng model='virtio'>
<rate period="2000" bytes="1234"/>
<backend model='random'>/dev/random</backend>
<!-- OR -->
<backend model='egd' type='udp'>
<source mode='bind' service='1234'/>
<source mode='connect' host='1.2.3.4' service='1234'/>
</backend>
<!-- OR -->
<backend model='builtin'/>
</rng>
</devices>
...
model
The required model attribute specifies what type
of RNG device is provided. Valid values are specific to
the virtualization platform:
rate
The optional rate element allows limiting the rate at
which entropy can be consumed from the source. The mandatory
attribute bytes specifies how many bytes are permitted
to be consumed per period. An optional period attribute
specifies the duration of a period in milliseconds; if omitted, the
period is taken as 1000 milliseconds (1 second).
Since 1.0.4
backend
The backend element specifies the source of entropy
to be used for the domain. The source model is configured using the
model attribute. Supported source models are:
random
This backend type expects a non-blocking character device
as input. The file name is specified as contents of the
backend element. Since
1.3.4 any path is accepted. Before that
/dev/random and /dev/hwrng were
the only accepted paths. When no file name is specified,
the hypervisor default is used. For QEMU, the default is
/dev/random. However, the recommended source
of entropy is /dev/urandom (as it doesn't
have the limitations of /dev/random).
egdThis backend connects to a source using the EGD protocol. The source is specified as a character device. Refer to character device host interface for more information.
builtin
This backend uses qemu builtin random generator, which uses
getrandom() syscall as the source of entropy.
(Since 6.1.0 and QEMU 4.2)
driverdriver can be used to tune the device:
The TPM device enables a QEMU guest to have access to TPM functionality. The TPM device may either be a TPM 1.2 or a TPM 2.0.
The TPM passthrough device type provides access to the host's TPM for one QEMU guest. No other software may be using the TPM device, typically /dev/tpm0, at the time the QEMU guest is started. 'passthrough' since 1.0.5
Example: usage of the TPM passthrough device
...
<devices>
<tpm model='tpm-tis'>
<backend type='passthrough'>
<device path='/dev/tpm0'/>
</backend>
</tpm>
</devices>
...
The emulator device type gives access to a TPM emulator providing
TPM functionality for each VM. QEMU talks to it over a Unix socket. With
the emulator device type each guest gets its own private TPM.
'emulator' since 4.5.0
The state of the TPM emulator can be encrypted by providing an
encryption element.
'encryption' since 5.6.0
Example: usage of the TPM Emulator
...
<devices>
<tpm model='tpm-tis'>
<backend type='emulator' version='2.0'>
<encryption secret='6dd3e4a5-1d76-44ce-961f-f119f5aad935'/>
</backend>
</tpm>
</devices>
...
model
The model attribute specifies what device
model QEMU provides to the guest. If no model name is provided,
tpm-tis will automatically be chosen for non-PPC64
architectures.
Since 4.4.0, another available choice
is the tpm-crb, which should only be used when the
backend device is a TPM 2.0. Since 6.1.0,
pSeries guests on PPC64 are supported and the default is
tpm-spapr.
backend
The backend element specifies the type of
TPM device. The following types are supported:
passthroughUse the host's TPM device.
This backend type requires exclusive access to a TPM device on
the host. An example for such a device is /dev/tpm0. The fully
qualified file name is specified by path attribute of the
source element. If no file name is specified then
/dev/tpm0 is automatically used.
emulatorFor this backend type the 'swtpm' TPM Emulator must be installed on the host. Libvirt will automatically start an independent TPM emulator for each QEMU guest requesting access to it.
version
The version attribute indicates the version
of the TPM. By default a TPM 1.2 is created. This attribute
only works with the emulator backend. The following
versions are supported:
encryption
The encryption element allows the state of a TPM emulator
to be encrypted. The secret must reference a secret object
that holds the passphrase from which the encryption key will be derived.
nvram device is always added to pSeries guest on PPC64, and its address
is allowed to be changed. Element nvram (only valid for
pSeries guest, since 1.0.5) is provided to
enable the address setting.
Example: usage of NVRAM configuration
...
<devices>
<nvram>
<address type='spapr-vio' reg='0x00003000'/>
</nvram>
</devices>
...
spapr-vioVIO device address type, only valid for PPC64.
regDevice address
panic device enables libvirt to receive panic notification from a QEMU guest. Since 1.2.1, QEMU and KVM only
This feature is always enabled for:
For the guest types listed above, libvirt automatically adds a
panic element to the domain XML.
Example: usage of panic configuration
...
<devices>
<panic model='hyperv'/>
<panic model='isa'>
<address type='isa' iobase='0x505'/>
</panic>
</devices>
...
model
The optional model attribute specifies what type
of panic device is provided. The panic model used when this attribute
is missing depends on the hypervisor and guest arch.
addressaddress of panic. The default ioport is 0x505. Most users don't need to specify an address, and doing so is forbidden altogether for s390, pseries and hyperv models.
A shared memory device allows to share a memory region between different virtual machines and the host. Since 1.2.10, QEMU and KVM only
...
<devices>
<shmem name='my_shmem0'>
<model type='ivshmem-plain'/>
<size unit='M'>4</size>
</shmem>
<shmem name='shmem_server'>
<model type='ivshmem-doorbell'/>
<size unit='M'>2</size>
<server path='/tmp/socket-shmem'/>
<msi vectors='32' ioeventfd='on'/>
</shmem>
</devices>
...
shmemshmem element has one mandatory attribute,
name to identify the shared memory. This attribute cannot
be directory specific to . or .. as well as
it cannot involve path separator /.
modeltype of the optional element model
specifies the model of the underlying device providing the
shmem device. The models currently supported are
ivshmem (supports both server and server-less shmem, but is
deprecated by newer QEMU in favour of the -plain and -doorbell variants),
ivshmem-plain (only for server-less shmem) and
ivshmem-doorbell (only for shmem with the server).
sizesize element specifies the size of the shared
memory. This must be power of 2 and greater than or equal to 1 MiB.
serverserver element can be used to configure a server
socket the device is supposed to connect to. The optional
path attribute specifies the absolute path to the unix socket
and defaults to /var/lib/libvirt/shmem/$shmem-$name-sock.
msimsi element enables/disables (values "on"/"off",
respectively) MSI interrupts. This option can currently be used only
together with the server element. The vectors
attribute can be used to specify the number of interrupt
vectors. The ioeventd attribute enables/disables (values
"on"/"off", respectively) ioeventfd.
In addition to the initial memory assigned to the guest, memory devices allow additional memory to be assigned to the guest in the form of memory modules. A memory device can be hot-plugged or hot-unplugged depending on the guests' memory resource needs. Some hypervisors may require NUMA configured for the guest.
Example: usage of the memory devices
...
<devices>
<memory model='dimm' access='private' discard='yes'>
<target>
<size unit='KiB'>524287</size>
<node>0</node>
</target>
</memory>
<memory model='dimm'>
<source>
<pagesize unit='KiB'>4096</pagesize>
<nodemask>1-3</nodemask>
</source>
<target>
<size unit='KiB'>524287</size>
<node>1</node>
</target>
</memory>
<memory model='nvdimm'>
<uuid>
<source>
<path>/tmp/nvdimm</path>
</source>
<target>
<size unit='KiB'>524288</size>
<node>1</node>
<label>
<size unit='KiB'>128</size>
</label>
<readonly/>
</target>
</memory>
<memory model='nvdimm' access='shared'>
<uuid>
<source>
<path>/dev/dax0.0</path>
<alignsize unit='KiB'>2048</alignsize>
<pmem/>
</source>
<target>
<size unit='KiB'>524288</size>
<node>1</node>
<label>
<size unit='KiB'>128</size>
</label>
</target>
</memory>
</devices>
...
model
Provide dimm to add a virtual DIMM module to the guest.
Since 1.2.14
Provide nvdimm model adds a Non-Volatile DIMM
module. Since 3.2.0
access
An optional attribute access
(since 3.2.0) that provides
capability to fine tune mapping of the memory on per
module basis. Values are the same as
Memory Backing:
shared and private.
For nvdimm model, if using real NVDIMM DAX device as
backend, shared is required.
discard
An optional attribute discard
(since 4.4.0) that provides
capability to fine tune discard of data on per module
basis. Accepted values are yes and
no. The feature is described here:
Memory Backing.
This attribute is allowed only for
model='dimm'.
uuid
For pSeries guests, an uuid can be set to identify the
nvdimm module. If absent, libvirt will generate an uuid.
automatically. This attribute is allowed only for
model='nvdimm' for pSeries guests.
Since 6.2.0
source
For model dimm this element is optional and allows to
fine tune the source of the memory used for the given memory device.
If the element is not provided defaults configured via
numatune are used. If dimm is provided,
then the following optional elements can be provided as well:
pagesizeThis element can be used to override the default host page size used for backing the memory device. The configured value must correspond to a page size supported by the host.
nodemaskThis element can be used to override the default set of NUMA nodes where the memory would be allocated.
For model nvdimm this element is mandatory. The
mandatory child element path represents a path in
the host that backs the nvdimm module in the guest. The following
optional elements may be used:
alignsize
The alignsize element defines the page size
alignment used to mmap the address range for the backend
path. If not supplied the host page size is used.
For example, to mmap a real NVDIMM device a 2M-aligned page may
be required, and host page size is 4KB, then we need to set this
element to 2MB.
Since 5.0.0
pmem
If persistent memory is supported and enabled by the hypervisor
in order to guarantee the persistence of writes to the vNVDIMM
backend, then use the pmem element in order to
utilize the feature.
Since 5.0.0
target
The mandatory target element configures the placement and
sizing of the added memory from the perspective of the guest.
The mandatory size subelement configures the size of the
added memory as a scaled integer.
The node subelement configures the guest NUMA node to
attach the memory to. The element shall be used only if the guest has
NUMA nodes configured.
The following optional elements may be used:
label
For NVDIMM type devices one can use label and its
subelement size to configure the size of
namespaces label storage within the NVDIMM module. The
size element has usual meaning described
here.
label is mandatory for pSeries guests and optional
for all other architectures.
For QEMU domains the following restrictions apply:
readonly
The readonly element is used to mark the vNVDIMM
as read-only. Only the real NVDIMM device backend can guarantee
the guest write persistence, so other backend types should use
the readonly element.
Since 5.0.0
The iommu element can be used to add an IOMMU device.
Since 2.1.0
Example:
...
<devices>
<iommu model='intel'>
<driver intremap='on'/>
</iommu>
</devices>
...
model
Supported values are intel (for Q35 guests) and,
since 5.5.0, smmuv3 (for
ARM virt guests).
driver
The driver subelement can be used to configure
additional options, some of which might only be available for
certain IOMMU models:
intremap
The intremap attribute with possible values
on and off can be used to
turn on interrupt remapping, a part of the VT-d functionality.
Currently this requires split I/O APIC
(<ioapic driver='qemu'/>).
Since 3.4.0 (QEMU/KVM only)
caching_mode
The caching_mode attribute with possible values
on and off can be used to
turn on the VT-d caching mode (useful for assigned devices).
Since 3.4.0 (QEMU/KVM only)
eim
The eim attribute (with possible values
on and off) can be used to
configure Extended Interrupt Mode. A q35 domain with
split I/O APIC (as described in
hypervisor features),
and both interrupt remapping and EIM turned on for
the IOMMU, will be able to use more than 255 vCPUs.
Since 3.4.0 (QEMU/KVM only)
iotlb
The iotlb attribute with possible values
on and off can be used to
turn on the IOTLB used to cache address translation
requests from devices.
Since 3.5.0 (QEMU/KVM only)
A vsock host/guest interface. The model attribute
defaults to virtio. Since 5.2.0
model can also be 'virtio-transitional' and
'virtio-non-transitional', see
Virtio transitional devices
for more details.
The optional attribute address of the cid
element specifies the CID assigned to the guest. If the attribute
auto is set to yes, libvirt
will assign a free CID automatically on domain startup.
Since 4.4.0
...
<devices>
<vsock model='virtio'>
<cid auto='no' address='3'/>
</vsock>
</devices>
...
The seclabel element allows control over the
operation of the security drivers. There are three basic
modes of operation, 'dynamic' where libvirt automatically
generates a unique security label, 'static' where the
application/administrator chooses the labels, or 'none'
where confinement is disabled. With dynamic
label generation, libvirt will always automatically
relabel any resources associated with the virtual machine.
With static label assignment, by default, the administrator
or application must ensure labels are set correctly on any
resources, however, automatic relabeling can be enabled
if desired. 'dynamic' since 0.6.1, 'static'
since 0.6.2, and 'none' since 0.9.10.
If more than one security driver is used by libvirt, multiple
seclabel tags can be used, one for each driver and
the security driver referenced by each tag can be defined using
the attribute model
Valid input XML configurations for the top-level security label are:
<seclabel type='dynamic' model='selinux'/>
<seclabel type='dynamic' model='selinux'>
<baselabel>system_u:system_r:my_svirt_t:s0</baselabel>
</seclabel>
<seclabel type='static' model='selinux' relabel='no'>
<label>system_u:system_r:svirt_t:s0:c392,c662</label>
</seclabel>
<seclabel type='static' model='selinux' relabel='yes'>
<label>system_u:system_r:svirt_t:s0:c392,c662</label>
</seclabel>
<seclabel type='none'/>
If no 'type' attribute is provided in the input XML, then the security driver default setting will be used, which may be either 'none' or 'dynamic'. If a 'baselabel' is set but no 'type' is set, then the type is presumed to be 'dynamic'
When viewing the XML for a running guest with automatic
resource relabeling active, an additional XML element,
imagelabel, will be included. This is an
output-only element, so will be ignored in user supplied
XML documents
typestatic, dynamic or none
to determine whether libvirt automatically generates a unique security
label or not.
modeldac is not available
when guest is run by unprivileged user.
relabelyes or no. This must always
be yes if dynamic label assignment is used. With
static label assignment it will default to no.
labelbaselabeltype field of the
baselabel in the generated label. Other fields are inherited from
the parent process when using SELinux baselabels.
(The example above demonstrates the use of my_svirt_t
as the value for the type field.)
imagelabelWhen relabeling is in effect, it is also possible to fine-tune
the labeling done for specific source file names, by either
disabling the labeling (useful if the file lives on NFS or other
file system that lacks security labeling) or requesting an
alternate label (useful when a management application creates a
special label to allow sharing of some, but not all, resources
between domains), since 0.9.9. When
a seclabel element is attached to a specific path
rather than the top-level domain assignment, only the
attribute relabel or the
sub-element label are supported. Additionally,
since 1.1.2, an output-only
element labelskip will be present for active
domains on disks where labeling was skipped due to the image
being on a file system that lacks security labeling.
The content of the optional keywrap element specifies
whether the guest will be allowed to perform the S390 cryptographic key
management operations. A clear key can be protected by encrypting it
under a unique wrapping key that is generated for each guest VM running
on the host. Two variations of wrapping keys are generated: one version
for encrypting protected keys using the DEA/TDEA algorithm, and another
version for keys encrypted using the AES algorithm. If a
keywrap element is not included, the guest will be granted
access to both AES and DEA/TDEA key wrapping by default.
<domain>
...
<keywrap>
<cipher name='aes' state='off'/>
</keywrap>
...
</domain>
At least one cipher element must be nested within the
keywrap element.
ciphername attribute identifies the algorithm
for encrypting a protected key. The values supported for this attribute
are aes for encryption under the AES wrapping key, or
dea for encryption under the DEA/TDEA wrapping key. The
state attribute indicates whether the cryptographic key
management operations should be turned on for the specified encryption
algorithm. The value can be set to on or off.
Note: DEA/TDEA is synonymous with DES/TDES.
The contents of the <launchSecurity type='sev'> element
is used to provide the guest owners input used for creating an encrypted
VM using the AMD SEV feature (Secure Encrypted Virtualization).
SEV is an extension to the AMD-V architecture which supports running
encrypted virtual machine (VMs) under the control of KVM. Encrypted
VMs have their pages (code and data) secured such that only the guest
itself has access to the unencrypted version. Each encrypted VM is
associated with a unique encryption key; if its data is accessed to a
different entity using a different key the encrypted guests data will
be incorrectly decrypted, leading to unintelligible data.
For more information see various input parameters and its format see the
SEV API spec
Since 4.4.0
<domain>
...
<launchSecurity type='sev'>
<policy>0x0001</policy>
<cbitpos>47</cbitpos>
<reducedPhysBits>1</reducedPhysBits>
<dhCert>RBBBSDDD=FDDCCCDDDG</dhCert>
<session>AAACCCDD=FFFCCCDSDS</session>
</launchSecurity>
...
</domain>
cbitposcbitpos element provides the C-bit (aka encryption bit)
location in guest page table entry. The value of cbitpos is
hypervisor dependent and can be obtained through the sev element
from the domain capabilities.
reducedPhysBitsreducedPhysBits element provides the physical
address bit reducation. Similar to cbitpos the value of
reduced-phys-bit is hypervisor dependent and can be obtained
through the sev element from the domain capabilities.
policypolicy element provides the guest policy
which must be maintained by the SEV firmware. This policy is enforced by
the firmware and restricts what configuration and operational commands
can be performed on this guest by the hypervisor. The guest policy
provided during guest launch is bound to the guest and cannot be changed
throughout the lifetime of the guest. The policy is also transmitted
during snapshot and migration flows and enforced on the destination platform.
The guest policy is a 4 unsigned byte with the fields shown in Table:
| Bit(s) | Description |
|---|---|
| 0 | Debugging of the guest is disallowed when set |
| 1 | Sharing keys with other guests is disallowed when set |
| 2 | SEV-ES is required when set |
| 3 | Sending the guest to another platform is disallowed when set |
| 4 | The guest must not be transmitted to another platform that is not in the domain when set. |
| 5 | The guest must not be transmitted to another platform that is not SEV capable when set. |
| 6:15 | reserved |
| 16:32 | The guest must not be transmitted to another platform with a lower firmware version. |
dhCertdhCert element provides the guest owners
base64 encoded Diffie-Hellman (DH) key. The key is used to negotiate a
master secret key between the SEV firmware and guest owner. This master
secret key is then used to establish a trusted channel between SEV
firmware and guest owner.
sessionsession element provides the guest owners
base64 encoded session blob defined in the SEV API spec.
See SEV spec LAUNCH_START section for the session blob format.
Example configurations for each driver are provide on the driver specific pages listed below