A new element is introduced to XML that allows to control
state of virtual network interfaces in hypervisors.

Live modification of the link state allows networking tools
propagate topology changes to guest OS or testing of
scenarios in complex (virtual) networks.

This patch adds elements to XML grammars and parsing and generating
code.

I got confused when 'virsh domblkinfo dom disk' required the
path to a disk (which can be ambiguous, since a single file
can back multiple disks), rather than the unambiguous target
device name that I was using in disk snapshots.  So, in true
developer fashion, I went for the best of both worlds - all
interfaces that operate on a disk (aka block) now accept
either the target name or the unambiguous path to the backing
file used by the disk.

* src/conf/domain_conf.h (virDomainDiskIndexByName): Add
parameter.
(virDomainDiskPathByName): New prototype.
* src/libvirt_private.syms (domain_conf.h): Export it.
* src/conf/domain_conf.c (virDomainDiskIndexByName): Also allow
searching by path, and decide whether ambiguity is okay.
(virDomainDiskPathByName): New function.
(virDomainDiskRemoveByName, virDomainSnapshotAlignDisks): Update
callers.
* src/qemu/qemu_driver.c (qemudDomainBlockPeek)
(qemuDomainAttachDeviceConfig, qemuDomainUpdateDeviceConfig)
(qemuDomainGetBlockInfo, qemuDiskPathToAlias): Likewise.
* src/qemu/qemu_process.c (qemuProcessFindDomainDiskByPath):
Likewise.
* src/libxl/libxl_driver.c (libxlDomainAttachDeviceDiskLive)
(libxlDomainDetachDeviceDiskLive, libxlDomainAttachDeviceConfig)
(libxlDomainUpdateDeviceConfig): Likewise.
* src/uml/uml_driver.c (umlDomainBlockPeek): Likewise.
* src/xen/xend_internal.c (xenDaemonDomainBlockPeek): Likewise.
* docs/formatsnapshot.html.in: Update documentation.
* tools/virsh.pod (domblkstat, domblkinfo): Likewise.
* docs/schemas/domaincommon.rng (diskTarget): Tighten pattern on
disk targets.
* docs/schemas/domainsnapshot.rng (disksnapshot): Update to match.
* tests/domainsnapshotxml2xmlin/disk_snapshot.xml: Update test.

Adds an optional element to <domainsnapshot>, which will be used
to give user control over external snapshot filenames on input,
and specify generated filenames on output.

For now, no driver accepts this element; that will come later.

<domainsnapshot>
  ...
  <disks>
    <disk name='vda' snapshot='no'/>
    <disk name='vdb' snapshot='internal'/>
    <disk name='vdc' snapshot='external'>
      <driver type='qcow2'/>
      <source file='/path/to/new'/>
    </disk>
  </disks>
  <domain>
    ...
    <devices>
      <disk ...>
        <driver name='qemu' type='raw'/>
        <target dev='vdc'/>
        <source file='/path/to/old'/>
      </disk>
    </devices>
  </domain>
</domainsnapshot>

* src/conf/domain_conf.h (_virDomainSnapshotDiskDef): New type.
(_virDomainSnapshotDef): Add new elements.
(virDomainSnapshotAlignDisks): New prototype.
* src/conf/domain_conf.c (virDomainSnapshotDiskDefClear)
(virDomainSnapshotDiskDefParseXML, disksorter)
(virDomainSnapshotAlignDisks): New functions.
(virDomainSnapshotDefParseString): Parse new fields.
(virDomainSnapshotDefFree): Clean them up.
(virDomainSnapshotDefFormat): Output them.
* src/libvirt_private.syms (domain_conf.h): Export new function.
* docs/schemas/domainsnapshot.rng (domainsnapshot, disksnapshot):
Add more xml.
* docs/formatsnapshot.html.in: Document it.
* tests/domainsnapshotxml2xmlin/disk_snapshot.xml: New test.
* tests/domainsnapshotxml2xmlout/disk_snapshot.xml: Update.

In order to distinguish disk snapshots from system checkpoints, a
new state value that is only valid for snapshots is helpful.

* include/libvirt/libvirt.h.in (VIR_DOMAIN_LAST): New placeholder.
* src/conf/domain_conf.h (virDomainSnapshotState): New enum mapping.
(VIR_DOMAIN_DISK_SNAPSHOT): New internal enum value.
* src/conf/domain_conf.c (virDomainState): Use placeholder.
(virDomainSnapshotState): Extend mapping by one for use in snapshot.
(virDomainSnapshotDefParseString, virDomainSnapshotDefFormat):
Handle new state.
(virDomainObjSetState, virDomainStateReasonToString)
(virDomainStateReasonFromString): Avoid compiler warnings.
* tools/virsh.c (vshDomainState, vshDomainStateReasonToString):
Likewise.
* src/libvirt_private.syms (domain_conf.h): Export new functions.
* docs/schemas/domainsnapshot.rng: Tighten state definition.
* docs/formatsnapshot.html.in: Document it.
* tests/domainsnapshotxml2xmlout/disk_snapshot.xml: New test.

As discussed here:
https://www.redhat.com/archives/libvir-list/2011-August/msg00361.html
https://www.redhat.com/archives/libvir-list/2011-August/msg00552.html

Adds snapshot attribute and transient sub-element:

<devices>
  <disk type=... snapshot='no|internal|external'>
    ...
    <transient/>
  </disk>
</devices>

* docs/schemas/domaincommon.rng (snapshot): New define.
(disk): Add snapshot and persistent attributes.
* docs/formatdomain.html.in: Document them.
* src/conf/domain_conf.h (virDomainDiskSnapshot): New enum.
(_virDomainDiskDef): New fields.
* tests/qemuxml2argvdata/qemuxml2argv-disk-transient.xml: New
test of rng, no args counterpart until qemu support is complete.
* tests/qemuxml2argvdata/qemuxml2argv-disk-snapshot.args: New
file, snapshot attribute does not affect args.
* tests/qemuxml2argvdata/qemuxml2argv-disk-snapshot.xml: Likewise.
* tests/qemuxml2argvtest.c (mymain): Run new test.

Just like VM saved state images (virsh save), snapshots MUST
track the inactive domain xml to detect any ABI incompatibilities.

The indentation is not perfect, but functionality comes before form.

Later patches will actually supply a full domain; for now, this
wires up the storage to support one, but doesn't ever generate one
in dumpxml output.

Happily, libvirt.c was already rejecting use of VIR_DOMAIN_XML_SECURE
from read-only connections, even though before this patch, there was
no information to be secured by the use of that flag.

And while we're at it, mark the libvirt snapshot metadata files
as internal-use only.

* src/libvirt.c (virDomainSnapshotGetXMLDesc): Document flag.
* src/conf/domain_conf.h (_virDomainSnapshotDef): Add member.
(virDomainSnapshotDefParseString, virDomainSnapshotDefFormat):
Update signature.
* src/conf/domain_conf.c (virDomainSnapshotDefFree): Clean up.
(virDomainSnapshotDefParseString): Optionally parse domain.
(virDomainSnapshotDefFormat): Output full domain.
* src/esx/esx_driver.c (esxDomainSnapshotCreateXML)
(esxDomainSnapshotGetXMLDesc): Update callers.
* src/vbox/vbox_tmpl.c (vboxDomainSnapshotCreateXML)
(vboxDomainSnapshotGetXMLDesc): Likewise.
* src/qemu/qemu_driver.c (qemuDomainSnapshotCreateXML)
(qemuDomainSnapshotLoad, qemuDomainSnapshotGetXMLDesc)
(qemuDomainSnapshotWriteMetadata): Likewise.
* docs/formatsnapshot.html.in: Rework doc example.
Based on a patch by Philipp Hahn.

Redefining a qemu snapshot requires a bit of a tweak to the common
snapshot parsing code, but the end result is quite nice.

Be careful that redefinitions do not introduce circular parent
chains.  Also, we don't want to allow conversion between online
and offline existing snapshots.  We could probably do some more
validation for snapshots that don't already exist to make sure
they are even feasible, by parsing qemu-img output, but that
can come later.

* src/conf/domain_conf.h (virDomainSnapshotParseFlags): New
internal flags.
* src/conf/domain_conf.c (virDomainSnapshotDefParseString): Alter
signature to take internal flags.
* src/esx/esx_driver.c (esxDomainSnapshotCreateXML): Update caller.
* src/vbox/vbox_tmpl.c (vboxDomainSnapshotCreateXML): Likewise.
* src/qemu/qemu_driver.c (qemuDomainSnapshotCreateXML): Support
new public flags.

Filtering for roots is pretty easy to do.

* src/conf/domain_conf.h (virDomainSnapshotObjListGetNames)
(virDomainSnapshotObjListNum): Update prototype.
* src/conf/domain_conf.c (virDomainSnapshotObjListCopyNames)
(virDomainSnapshotObjListGetNames, virDomainSnapshotObjListCount)
(virDomainSnapshotObjListNum): Support filtering.
* src/qemu/qemu_driver.c (qemuDomainSnapshotNum)
(qemuDomainSnapshotListNames): Update callers.

Similar to the last patch in isolating the filtering from the
client actions, so that clients don't have to reinvent the
filtering.

* src/conf/domain_conf.h (virDomainSnapshotForEachChild): New
prototype.
* src/libvirt_private.syms (domain_conf.h): Export it.
* src/conf/domain_conf.c (virDomainSnapshotActOnChild)
(virDomainSnapshotForEachChild): New functions.
(virDomainSnapshotCountChildren): Delete.
(virDomainSnapshotHasChildren): Simplify.
* src/qemu/qemu_driver.c (qemuDomainSnapshotReparentChildren)
(qemuDomainSnapshotDelete): Likewise.

This one's nasty.  Ever since we fixed virHashForEach to prevent
nested hash iterations for safety reasons (commit fba550f6),
virDomainSnapshotDelete with VIR_DOMAIN_SNAPSHOT_DELETE_CHILDREN
has been broken for qemu: it deletes children, while leaving
grandchildren intact but pointing to a no-longer-present parent.
But even before then, the code would often appear to succeed to
clean up grandchildren, but risked memory corruption if you have
a large and deep hierarchy of snapshots.

For acting on just children, a single virHashForEach is sufficient.
But for acting on an entire subtree, it requires iteration; and
since we declared recursion as invalid, we have to switch to a
while loop.  Doing this correctly requires quite a bit of overhaul,
so I added a new helper function to isolate the algorithm from the
actions, so that callers do not have to reinvent the iteration.

Note that this _still_ does not handle CHILDREN correctly if one
of the children is the current snapshot; that will be next.

* src/conf/domain_conf.h (_virDomainSnapshotDef): Add mark.
(virDomainSnapshotForEachDescendant): New prototype.
* src/libvirt_private.syms (domain_conf.h): Export it.
* src/conf/domain_conf.c (virDomainSnapshotMarkDescendant)
(virDomainSnapshotActOnDescendant)
(virDomainSnapshotForEachDescendant): New functions.
* src/qemu/qemu_driver.c (qemuDomainSnapshotDiscardChildren):
Replace...
(qemuDomainSnapshotDiscardDescenent): ...with callback that
doesn't nest hash traversal.
(qemuDomainSnapshotDelete): Use new function.

- create a new "redirdev" element for this purpose

So that devices can be attached to hubs. Example, to attach to first
port of a usb-hub on port 1.

      <hub type='usb'>
         <address type='usb' bus='0' port='1'/>
      </hub>

      <input type='mouse' type='usb'>
         <address type='usb' bus='0' port='1.1'/>
      </hub>

also add a test entry

domain parsing and serialization code, qemu driver backend and
a couple of test

Companion controllers take an extra 'master' attribute to associate
them.

Also add tests for this

Expand the domain and the QEmu driver code
Adds a couple of tests

The model by default is piix3-uchi.

Example:
<controller type='usb' index='0' model='ich9-ehci'/>

List is: piix3-uhci piix4-uhci ehci ich9-ehci1 ich9-uhci1 ich9-uhci2
ich9-uhci3 vt82c686b-uhci pci-ohci

Since we are about to add USB controller support let's remove the
ambiguity

Newer QEMU introduced cache=directsync for -drive, this patchset
is to expose it in libvirt layer.

  * Introduced a new QEMU capability flag ($prefix_CACHE_DIRECTSYNC),
    As even $prefix_CACHE_V2 is set, we can't known if directsync
    is supported.

Audit all changes to the qemu vm->current_snapshot, and make them
update the saved xml file for both the previous and the new
snapshot, so that there is always at most one snapshot with
<active>1</active> in the xml, and that snapshot is used as the
current snapshot even across libvirtd restarts.

This patch does not fix the case of virDomainSnapshotDelete(,CHILDREN)
where one of the children is the current snapshot; that will be later.

* src/conf/domain_conf.h (_virDomainSnapshotDef): Alter member
type and name.
* src/conf/domain_conf.c (virDomainSnapshotDefParseString)
(virDomainSnapshotDefFormat): Update clients.
* docs/schemas/domainsnapshot.rng: Tighten rng.
* src/qemu/qemu_driver.c (qemuDomainSnapshotLoad): Reload current
snapshot.
(qemuDomainSnapshotCreateXML, qemuDomainRevertToSnapshot)
(qemuDomainSnapshotDiscard): Track current snapshot.

In some versions of qemu, both virtio-blk-pci and virtio-net-pci
devices can have an event_idx setting that determines some details of
event processing. When it is enabled, it "reduces the number of
interrupts and exits for the guest". qemu will automatically enable
this feature when it is available, but there may be cases where this
new feature could actually make performance worse (NB: no such case
has been found so far).

As a safety switch in case such a situation is encountered in the
field, this patch adds a new attribute "event_idx" to the <driver>
element of both disk and interface devices. event_idx can be set to
"on" (to force event_idx on in case qemu has it disabled by default)
or "off" (for force event_idx off). In the case that event_idx support
isn't present in qemu, the attribute is ignored (this on the advice of
the qemu developer).

docs/formatdomain.html.in: document the new flag (marking it as
   "don't mess with this!"
docs/schemas/domain.rng: add event_idx in appropriate places
src/conf/domain_conf.[ch]: add event_idx to parser and formatter
src/libvirt_private.syms: export
   virDomainVirtioEventIdx(From|To)String
src/qemu/qemu_capabilities.[ch]: detect and report event_idx in
   disk/net
src/qemu/qemu_command.c: add event_idx parameter to qemu commandline
    when appropriate.
tests/qemuxml2argvdata/qemuxml2argv-event_idx.args,
tests/qemuxml2argvdata/qemuxml2argv-event_idx.xml,
tests/qemuxml2argvtest.c,
tests/qemuxml2xmltest.c: test cases for event_idx.

In preparation for storing the domain description with the snapshot,
swap the order of declaration.
Signed-off-by: NPhilipp Hahn <hahn@univention.de>

Originally noticed by comparing the xml generated by virDomainSave
with the xml produced by reparsing and redumping that xml, but I
also did an audit of every last use of VIR_DOMAIN_XML_INACTIVE in
domain_conf.c to ensure that no other discrepancies exist.

* src/conf/domain_conf.c (virDomainDeviceInfoIsSet): Add
parameter, and update all callers.  Make static.
(virDomainNetDefFormat): Skip generated ifname.
(virDomainDefFormatInternal): Skip default <seclabel>.
(virDomainChrSourceDefParseXML): Skip generated pty path, and add
parameter.  Update callers.
* src/conf/domain_conf.h (virDomainDeviceInfoIsSet): Delete.
* src/libvirt_private.syms (domain_conf.h): Update.

Using a macro ensures that all the code is looking for the same
prefix.

* src/conf/domain_conf.h (VIR_NET_GENERATED_PREFIX): New macro.
* src/conf/domain_conf.c (virDomainNetDefParseXML): Use it.
* src/uml/uml_conf.c (umlConnectTapDevice): Likewise.
* src/qemu/qemu_command.c (qemuNetworkIfaceConnect): Likewise.
Suggested by Laine Stump.

Once it's plugged in, the <listen> element will be an optional
replacement for the "listen" attribute that graphics elements already
have. If the <listen> element is type='address', it will have an
attribute called 'address' which will contain an IP address or dns
name that the guest's display server should listen on. If, however,
type='network', the <listen> element should have an attribute called
'network' that will be set to the name of a network configuration to
get the IP address from.

* docs/schemas/domain.rng: updated to allow the <listen> element

* docs/formatdomain.html.in: document the <listen> element and its
  attributes.

* src/conf/domain_conf.[hc]:

  1) The domain parser, formatter, and data structure are modified to
     support 0 or more <listen> subelements to each <graphics>
     element. The old style "legacy" listen attribute is also still
     accepted, and will be stored internally just as if it were a
     separate <listen> element. On output (i.e. format), the address
     attribute of the first <listen> element of type 'address' will be
     duplicated in the legacy "listen" attribute of the <graphic>
     element.

  2) The "listenAddr" attribute has been removed from the unions in
     virDomainGRaphicsDef for graphics types vnc, rdp, and spice.
     This attribute is now in the <listen> subelement (aka
     virDomainGraphicsListenDef)

  3) Helper functions were written to provide simple access
     (both Get and Set) to the listen elements and their attributes.

* src/libvirt_private.syms: export the listen helper functions

* src/qemu/qemu_command.c, src/qemu/qemu_hotplug.c,
  src/qemu/qemu_migration.c, src/vbox/vbox_tmpl.c,
  src/vmx/vmx.c, src/xenxs/xen_sxpr.c, src/xenxs/xen_xm.c

  Modify all these files to use the listen helper functions rather
  than directly referencing the (now missing) listenAddr
  attribute. There can be multiple <listen> elements to a single
  <graphics>, but the drivers all currently only support one, so all
  replacements of direct access with a helper function indicate index
  "0".

* tests/* - only 3 of these are new files added explicitly to test the
  new <listen> element. All the others have been modified to reflect
  the fact that any legacy "listen" attributes passed in to the domain
  parse will be saved in a <listen> element (i.e. one of the
  virDomainGraphicsListenDefs), and during the domain format function,
  both the <listen> element as well as the legacy attributes will be
  output.

Every DomainNetDef has a bandwidth, as does every portgroup.
Whenever a DomainNetDef of type NETWORK is about to be used, a call is
made to networkAllocateActualDevice(). This function chooses the "best"
bandwidth object and places it in the DomainActualNetDef.
From that point on, whenever some code needs to use the bandwidth data
for the interface, it's retrieved with virDomainNetGetActualBandwidth(),
which will always return the "best" info as determined in the
previous step.

These functions parse given XML node and return pointer to the
output. Unknown elements are silently ignored. Attributes must
be integer and must fit in unsigned long long.

Free function frees elements of virBandwidth structure.

the domain XML <interface> element is updated in the following ways:

1) <virtualportprofile> can be specified when source type='network'
(previously it was only valid for source type='direct')

2) A new attribute "portgroup" has been added to the <source>
element. When source type='network' (the only time portgroup is
recognized), extra configuration information will be taken from the
<portgroup> element of the given name in the network definition.

3) Each virDomainNetDef now also potentially has a
virDomainActualNetDef which is a private object (never
exported/imported via the public API, and not defined in the RNG) that
is used to maintain information about the physical device that was
actually used for a NetDef of type VIR_DOMAIN_NET_TYPE_NETWORK.

The virDomainActualNetDef will only be parsed/formatted if the
parse/format function is called with the
VIR_DOMAIN_XML_INTERNAL_ACTUAL_NET flag set (which is only needed when
saving/loading a running domain's state info to the stateDir).

The virtPortProfile in the domain interface struct is now a separately
allocated object *pointed to by* (rather than contained in) the main
virDomainNetDef object. This is done to make it easier to figure out
when a virtualPortProfile has/hasn't been specified in a particular
config.

This patch implements period and quota tunable XML configuration and parsing.
A quota or period of zero will be simply ignored.

There were two API in driver.c that were silently masking flags
bits prior to calling out to the drivers, and several others
that were explicitly masking flags bits.  This is not
forward-compatible - if we ever have that many flags in the
future, then talking to an old server that masks out the
flags would be indistinguishable from talking to a new server
that can honor the flag.  In general, libvirt.c should forward
_all_ flags on to drivers, and only the drivers should reject
unknown flags.

In the case of virDrvSecretGetValue, the solution is to separate
the internal driver callback function to have two parameters
instead of one, with only one parameter affected by the public
API.  In the case of virDomainGetXMLDesc, it turns out that
no one was ever mixing VIR_DOMAIN_XML_INTERNAL_STATUS with
the dumpxml path in the first place; that internal flag was
only used in saving and restoring state files, which happened
to be in functions internal to a single file, so there is no
mixing of the internal flag with a public flags argument.
Additionally, virDomainMemoryStats passed a flags argument
over RPC, but not to the driver.

* src/driver.h (VIR_DOMAIN_XML_FLAGS_MASK)
(VIR_SECRET_GET_VALUE_FLAGS_MASK): Delete.
(virDrvSecretGetValue): Separate out internal flags.
(virDrvDomainMemoryStats): Provide missing flags argument.
* src/driver.c (verify): Drop unused check.
* src/conf/domain_conf.h (virDomainObjParseFile): Delete
declaration.
(virDomainXMLInternalFlags): Move...
* src/conf/domain_conf.c: ...here.  Delete redundant include.
(virDomainObjParseFile): Make static.
* src/libvirt.c (virDomainGetXMLDesc, virSecretGetValue): Update
clients.
(virDomainMemoryPeek, virInterfaceGetXMLDesc)
(virDomainMemoryStats, virDomainBlockPeek, virNetworkGetXMLDesc)
(virStoragePoolGetXMLDesc, virStorageVolGetXMLDesc)
(virNodeNumOfDevices, virNodeListDevices, virNWFilterGetXMLDesc):
Don't mask unknown flags.
* src/interface/netcf_driver.c (interfaceGetXMLDesc): Reject
unknown flags.
* src/secret/secret_driver.c (secretGetValue): Update clients.
* src/remote/remote_driver.c (remoteSecretGetValue)
(remoteDomainMemoryStats): Likewise.
* src/qemu/qemu_process.c (qemuProcessGetVolumeQcowPassphrase):
Likewise.
* src/qemu/qemu_driver.c (qemudDomainMemoryStats): Likewise.
* daemon/remote.c (remoteDispatchDomainMemoryStats): Likewise.

Given a PID, the QEMU driver reads /proc/$PID/cmdline and
/proc/$PID/environ to get the configuration. This is fed
into the ARGV->XML convertor to build an XML configuration
for the process.

/proc/$PID/exe is resolved to identify the full command
binary path

After checking for name/uuid uniqueness, an attempt is
made to connect to the monitor socket. If successful
then 'info status' and 'info kvm' are issued to determine
whether the CPUs are running and if KVM is enabled.

* src/qemu/qemu_driver.c: Implement virDomainQemuAttach
* src/qemu/qemu_process.h, src/qemu/qemu_process.c: Add
  qemuProcessAttach to connect to the monitor of an
  existing QEMU process

The drivers were accepting domain configs without checking if those
were actually meant for them. For example the LXC driver happily
accepts configs with type QEMU.

Add a check for the expected domain types to the virDomainDefParse*
functions.

This patch creates new <bios> element which, at this time has only the
attribute useserial='yes|no'. This attribute allow users to use
Serial Graphics Adapter and see BIOS messages from the very first moment
domain boots up. Therefore, users can choose boot medium, set PXE, etc.

This option accepts 3 values:
-keep, to keep current client connected (Spice+VNC)
-disconnect, to disconnect client (Spice)
-fail, to fail setting password if there is a client connected (Spice)

When no <seclabel> is present in the XML, the virDomainSeclabelDef
struct is left as all zeros. Unfortunately, this means it gets setup
as type=dynamic, with relabel=no, which is an illegal combination.

Change the 'bool relabel' attribute in virDomainSeclabelDef to
the inverse 'bool norelabel' so that the default initialization
is sensible

* src/conf/domain_conf.c, src/conf/domain_conf.h,
  src/security/security_apparmor.c, src/security/security_selinux.c:
  Replace 'relabel' with 'norelabel'

* Change all flags args from int to unsigned int

* Allow passing flags in virDomainObjParseFile (and propogate those
  flags all the way down the call chain). Previously the flags were
  hardcoded (to VIR_DOMAIN_XML_INTERNAL_STATUS) several layers down
  the chain. Pass that value in at the one place that is currently
  calling virDomainObjParseFile.

Add a new attribute to the <seclabel> XML to allow resource
relabelling to be enabled with static label usage.

  <seclabel model='selinux' type='static' relabel='yes'>
    <label>system_u:system_r:svirt_t:s0:c392,c662</label>
  </seclabel>

* docs/schemas/domain.rng: Add relabel attribute
* src/conf/domain_conf.c, src/conf/domain_conf.h: Parse
  the 'relabel' attribute
* src/qemu/qemu_process.c: Unconditionally clear out the
  'imagelabel' attribute
* src/security/security_apparmor.c: Skip based on 'relabel'
  attribute instead of label type
* src/security/security_selinux.c: Skip based on 'relabel'
  attribute instead of label type and fill in <imagelabel>
  attribute if relabel is enabled.

Normally the dynamic labelling mode will always use a base
label of 'svirt_t' for VMs. Introduce a <baselabel> field
in the <seclabel> XML to allow this base label to be changed

eg

   <seclabel type='dynamic' model='selinux'>
     <baselabel>system_u:object_r:virt_t:s0</baselabel>
   </seclabel>

* docs/schemas/domain.rng: Add <baselabel>
* src/conf/domain_conf.c, src/conf/domain_conf.h: Parsing
  of base label
* src/qemu/qemu_process.c: Don't reset 'model' attribute if
  a base label is specified
* src/security/security_apparmor.c: Refuse to support base label
* src/security/security_selinux.c: Use 'baselabel' when generating
  label, if available