Use the new virDomainUpdateDeviceFlags API to allow the VNC password
to be changed on the fly

* src/internal.h: Define STREQ_NULLABLE() which is like STREQ()
  but does not crash if either argument is NULL, and treats two
  NULLs as equal.
* src/libvirt_private.syms: Export virDomainGraphicsTypeToString
* src/qemu/qemu_driver.c: Support VNC password change on a live
  machine
* src/qemu/qemu_monitor.c: Disable crazy debugging info. Treat a
  NULL password as "" (empty string), allowing passwords to be
  disabled in the monitor

To allow the new virDomainUpdateDeviceFlags() API to be universally
used with all drivers, this patch adds an impl to all the current
drivers which support CDROM or Floppy disk media change via the
current virDomainAttachDeviceFlags API

* src/qemu/qemu_driver.c, src/vbox/vbox_tmpl.c,
  src/xen/proxy_internal.c, src/xen/xen_driver.c,
  src/xen/xend_internal.c: Implement media change via the
  virDomainUpdateDeviceFlags API
* src/xen/xen_driver.h, src/xen/xen_hypervisor.c,
  src/xen/xen_inotify.c, src/xen/xm_internal.c,
  src/xen/xs_internal.c: Stubs for Xen driver entry points

The current virDomainAttachDevice API can be (ab)used to change
the media of an existing CDROM/Floppy device. Going forward there
will be more devices that can be configured on the fly and overloading
virDomainAttachDevice for this is not too pleasant. This patch adds
a new virDomainUpdateDeviceFlags() explicitly just for modifying
existing devices.

* include/libvirt/libvirt.h.in: Add virDomainUpdateDeviceFlags
* src/driver.h: Internal API for virDomainUpdateDeviceFlags
* src/libvirt.c, src/libvirt_public.syms: Glue public API to
  driver API
* src/esx/esx_driver.c, src/lxc/lxc_driver.c, src/opennebula/one_driver.c,
  src/openvz/openvz_driver.c, src/phyp/phyp_driver.c, src/qemu/qemu_driver.c,
  src/remote/remote_driver.c, src/test/test_driver.c, src/uml/uml_driver.c,
  src/vbox/vbox_tmpl.c, src/xen/xen_driver.c, src/xenapi/xenapi_driver.c: Add
  stubs for new driver entry point

This introduces a new event type

   VIR_DOMAIN_EVENT_ID_GRAPHICS

The same event can be emitted in 3 scenarios

  typedef enum {
      VIR_DOMAIN_EVENT_GRAPHICS_CONNECT = 0,
      VIR_DOMAIN_EVENT_GRAPHICS_INITIALIZE,
      VIR_DOMAIN_EVENT_GRAPHICS_DISCONNECT,
  } virDomainEventGraphicsPhase;

Connect/disconnect are triggered at socket accept/close.
The initialize phase is immediately after the protocol
setup and authentication has completed. ie when the
client is authorized and about to start interacting with
the graphical desktop

This event comes with *a lot* of potential information

 - IP address, port & address family of client
 - IP address, port & address family of server
 - Authentication scheme (arbitrary string)
 - Authenticated subject identity. A subject may have
   multiple identities with some authentication schemes.
   For example, vencrypt+sasl results in a x509dname
   and saslUsername identities.

This results in a very complicated callback :-(

   typedef enum {
      VIR_DOMAIN_EVENT_GRAPHICS_ADDRESS_IPV4,
      VIR_DOMAIN_EVENT_GRAPHICS_ADDRESS_IPV6,
   } virDomainEventGraphicsAddressType;

   struct _virDomainEventGraphicsAddress {
       int family;
       const char *node;
       const char *service;
   };
   typedef struct _virDomainEventGraphicsAddress virDomainEventGraphicsAddress;
   typedef virDomainEventGraphicsAddress *virDomainEventGraphicsAddressPtr;

   struct _virDomainEventGraphicsSubject {
      int nidentity;
      struct {
          const char *type;
          const char *name;
      } *identities;
   };
   typedef struct _virDomainEventGraphicsSubject virDomainEventGraphicsSubject;
   typedef virDomainEventGraphicsSubject *virDomainEventGraphicsSubjectPtr;

   typedef void (*virConnectDomainEventGraphicsCallback)(virConnectPtr conn,
                                                         virDomainPtr dom,
                                                         int phase,
                                                         virDomainEventGraphicsAddressPtr local,
                                                         virDomainEventGraphicsAddressPtr remote,
                                                         const char *authScheme,
                                                         virDomainEventGraphicsSubjectPtr subject,
                                                         void *opaque);

The wire protocol is similarly complex

   struct remote_domain_event_graphics_address {
     int family;
     remote_nonnull_string node;
     remote_nonnull_string service;
   };

   const REMOTE_DOMAIN_EVENT_GRAPHICS_IDENTITY_MAX = 20;

   struct remote_domain_event_graphics_identity {
     remote_nonnull_string type;
     remote_nonnull_string name;
   };

   struct remote_domain_event_graphics_msg {
     remote_nonnull_domain dom;
     int phase;
     remote_domain_event_graphics_address local;
     remote_domain_event_graphics_address remote;
     remote_nonnull_string authScheme;
     remote_domain_event_graphics_identity subject<REMOTE_DOMAIN_EVENT_GRAPHICS_IDENTITY_MAX>;
   };

This is currently implemented in QEMU for the VNC graphics
protocol, but designed to be usable with SPICE graphics in
the future too.

* daemon/remote.c: Dispatch graphics events to client
* examples/domain-events/events-c/event-test.c: Watch for
  graphics events
* include/libvirt/libvirt.h.in: Define new graphics event ID
  and callback signature
* src/conf/domain_event.c, src/conf/domain_event.h,
  src/libvirt_private.syms: Extend API to handle graphics events
* src/qemu/qemu_driver.c: Connect to the QEMU monitor event
  for VNC events and emit a libvirt graphics event
* src/remote/remote_driver.c: Receive and dispatch graphics
  events to application
* src/remote/remote_protocol.x: Wire protocol definition for
  graphics events
* src/qemu/qemu_monitor.c, src/qemu/qemu_monitor.h,
  src/qemu/qemu_monitor_json.c: Watch for VNC_CONNECTED,
  VNC_INITIALIZED & VNC_DISCONNETED events from QEMU monitor

This introduces a new event type

   VIR_DOMAIN_EVENT_ID_IO_ERROR

This event includes the action that is about to be taken
as a result of the watchdog triggering

  typedef enum {
     VIR_DOMAIN_EVENT_IO_ERROR_NONE = 0,
     VIR_DOMAIN_EVENT_IO_ERROR_PAUSE,
     VIR_DOMAIN_EVENT_IO_ERROR_REPORT,
  } virDomainEventIOErrorAction;

In addition it has the source path of the disk that had the
error and its unique device alias. It does not include the
target device name (/dev/sda), since this would preclude
triggering IO errors from other file backed devices (eg
serial ports connected to a file)

Thus there is a new callback definition for this event type

typedef void (*virConnectDomainEventIOErrorCallback)(virConnectPtr conn,
                                                     virDomainPtr dom,
                                                     const char *srcPath,
                                                     const char *devAlias,
                                                     int action,
                                                     void *opaque);

This is currently wired up to the QEMU block IO error events

* daemon/remote.c: Dispatch IO error events to client
* examples/domain-events/events-c/event-test.c: Watch for
  IO error events
* include/libvirt/libvirt.h.in: Define new IO error event ID
  and callback signature
* src/conf/domain_event.c, src/conf/domain_event.h,
  src/libvirt_private.syms: Extend API to handle IO error events
* src/qemu/qemu_driver.c: Connect to the QEMU monitor event
  for block IO errors and emit a libvirt IO error event
* src/remote/remote_driver.c: Receive and dispatch IO error
  events to application
* src/remote/remote_protocol.x: Wire protocol definition for
  IO error events
* src/qemu/qemu_monitor.c, src/qemu/qemu_monitor.h,
  src/qemu/qemu_monitor_json.c: Watch for BLOCK_IO_ERROR event
  from QEMU monitor

This introduces a new event type

   VIR_DOMAIN_EVENT_ID_WATCHDOG

This event includes the action that is about to be taken
as a result of the watchdog triggering

 typedef enum {
     VIR_DOMAIN_EVENT_WATCHDOG_NONE = 0,
     VIR_DOMAIN_EVENT_WATCHDOG_PAUSE,
     VIR_DOMAIN_EVENT_WATCHDOG_RESET,
     VIR_DOMAIN_EVENT_WATCHDOG_POWEROFF,
     VIR_DOMAIN_EVENT_WATCHDOG_SHUTDOWN,
     VIR_DOMAIN_EVENT_WATCHDOG_DEBUG,
 } virDomainEventWatchdogAction;

Thus there is a new callback definition for this event type

 typedef void (*virConnectDomainEventWatchdogCallback)(virConnectPtr conn,
                                                       virDomainPtr dom,
                                                       int action,
                                                       void *opaque);

* daemon/remote.c: Dispatch watchdog events to client
* examples/domain-events/events-c/event-test.c: Watch for
  watchdog events
* include/libvirt/libvirt.h.in: Define new watchdg event ID
  and callback signature
* src/conf/domain_event.c, src/conf/domain_event.h,
  src/libvirt_private.syms: Extend API to handle watchdog events
* src/qemu/qemu_driver.c: Connect to the QEMU monitor event
  for watchdogs and emit a libvirt watchdog event
* src/remote/remote_driver.c: Receive and dispatch watchdog
  events to application
* src/remote/remote_protocol.x: Wire protocol definition for
  watchdog events
* src/qemu/qemu_monitor.c, src/qemu/qemu_monitor.h,
  src/qemu/qemu_monitor_json.c: Watch for WATCHDOG event
  from QEMU monitor

This introduces a new event type

   VIR_DOMAIN_EVENT_ID_RTC_CHANGE

This event includes the new UTC offset measured in seconds.
Thus there is a new callback definition for this event type

 typedef void (*virConnectDomainEventRTCChangeCallback)(virConnectPtr conn,
                                                        virDomainPtr dom,
                                                        long long utcoffset,
                                                        void *opaque);

If the guest XML configuration for the <clock> is set to
offset='variable', then the XML will automatically be
updated with the new UTC offset value. This ensures that
during migration/save/restore the new offset is preserved.

* daemon/remote.c: Dispatch RTC change events to client
* examples/domain-events/events-c/event-test.c: Watch for
  RTC change events
* include/libvirt/libvirt.h.in: Define new RTC change event ID
  and callback signature
* src/conf/domain_event.c, src/conf/domain_event.h,
  src/libvirt_private.syms: Extend API to handle RTC change events
* src/qemu/qemu_driver.c: Connect to the QEMU monitor event
  for RTC changes and emit a libvirt RTC change event
* src/remote/remote_driver.c: Receive and dispatch RTC change
  events to application
* src/remote/remote_protocol.x: Wire protocol definition for
  RTC change events
* src/qemu/qemu_monitor.c, src/qemu/qemu_monitor.h,
  src/qemu/qemu_monitor_json.c: Watch for RTC_CHANGE event
  from QEMU monitor

The reboot event is not a normal lifecycle event, since the
virtual machine on the host does not change state. Rather the
guest OS is resetting the virtual CPUs. ie, the QEMU process
does not restart. Thus, this does not belong in the current
lifecycle events callback.

This introduces a new event type

    VIR_DOMAIN_EVENT_ID_REBOOT

It takes no parameters, besides the virDomainPtr, so it can
use the generic callback signature.

* daemon/remote.c: Dispatch reboot events to client
* examples/domain-events/events-c/event-test.c: Watch for
  reboot events
* include/libvirt/libvirt.h.in: Define new reboot event ID
* src/conf/domain_event.c, src/conf/domain_event.h,
  src/libvirt_private.syms: Extend API to handle reboot events
* src/qemu/qemu_driver.c: Connect to the QEMU monitor event
  for reboots and emit a libvirt reboot event
* src/remote/remote_driver.c: Receive and dispatch reboot
  events to application
* src/remote/remote_protocol.x: Wire protocol definition for
  reboot events

The libvirtd daemon impl will need to switch over to using the
new event APIs. To make this simpler, ensure all drivers currently
providing events support both the new APIs and old APIs.

* src/lxc/lxc_driver.c, src/qemu/qemu_driver.c, src/test/test_driver.c,
  src/vbox/vbox_tmpl.c, src/xen/xen_driver.c: Implement the new
  virConnectDomainEvent(Dereg|Reg)isterAny driver entry points

The internal domain events APIs are designed to handle the lifecycle
events. This needs to be refactored to allow arbitrary new event
types to be handled.

 * The signature of virDomainEventDispatchFunc changes to use
   virConnectDomainEventGenericCallback instead of the lifecycle
   event specific virConnectDomainEventCallback
 * Every registered callback gains a unique ID to allow its
   removal based on ID, instead of function pointer
 * Every registered callback gains an 'eventID' to allow callbacks
   for different types of events to be distinguished
 * virDomainEventDispatch is adapted to filter out callbacks
   whose eventID does not match the eventID of the event being
   dispatched
 * virDomainEventDispatch is adapted to filter based on the
   domain name and uuid, if this filter is set for a callback.
 * virDomainEvent type/detail fields are moved into a union to
   allow different data fields for other types of events to be
   added later

* src/conf/domain_event.h, src/conf/domain_event.c: Refactor
  to allow handling of different types of events
* src/lxc/lxc_driver.c, src/qemu/qemu_driver.c,
  src/remote/remote_driver.c, src/test/test_driver.c,
  src/xen/xen_driver.c: Change dispatch function signature
  to use virConnectDomainEventGenericCallback

The current API for domain events has a number of problems

 - Only allows for domain lifecycle change events
 - Does not allow the same callback to be registered multiple times
 - Does not allow filtering of events to a specific domain

This introduces a new more general purpose domain events API

  typedef enum {
     VIR_DOMAIN_EVENT_ID_LIFECYCLE = 0,       /* virConnectDomainEventCallback */
      ...more events later..
  }

  int virConnectDomainEventRegisterAny(virConnectPtr conn,
                                       virDomainPtr dom, /* Optional, to filter */
                                       int eventID,
                                       virConnectDomainEventGenericCallback cb,
                                       void *opaque,
                                       virFreeCallback freecb);

  int virConnectDomainEventDeregisterAny(virConnectPtr conn,
                                         int callbackID);

Since different event types can received different data in the callback,
the API is defined with a generic callback. Specific events will each
have a custom signature for their callback. Thus when registering an
event it is neccessary to cast the callback to the generic signature

eg

  int myDomainEventCallback(virConnectPtr conn,
                            virDomainPtr dom,
                            int event,
                            int detail,
                            void *opaque)
  {
    ...
  }

  virConnectDomainEventRegisterAny(conn, NULL,
                                   VIR_DOMAIN_EVENT_ID_LIFECYCLE,
                                   VIR_DOMAIN_EVENT_CALLBACK(myDomainEventCallback)
                                   NULL, NULL);

The VIR_DOMAIN_EVENT_CALLBACK() macro simply does a "bad" cast
to the generic signature

* include/libvirt/libvirt.h.in: Define new APIs for registering
  domain events
* src/driver.h: Internal driver entry points for new events APIs
* src/libvirt.c: Wire up public API to driver API for events APIs
* src/libvirt_public.syms: Export new APIs
* src/esx/esx_driver.c, src/lxc/lxc_driver.c, src/opennebula/one_driver.c,
  src/openvz/openvz_driver.c, src/phyp/phyp_driver.c,
  src/qemu/qemu_driver.c, src/remote/remote_driver.c,
  src/test/test_driver.c, src/uml/uml_driver.c,
  src/vbox/vbox_tmpl.c, src/xen/xen_driver.c,
  src/xenapi/xenapi_driver.c: Stub out new API entries

"virsh dominfo <vm>" crashes if there's no primary security driver set
since we only intialize the secmodel.model and secmodel.doi if we have
one. Attached patch checks for securityPrimaryDriver instead of
securityDriver since the later is always set in qemudSecurityInit().

Closes: http://bugs.debian.org/574359

Attempt to turn on vhost-net mode for devices of type NETWORK, BRIDGE,
and DIRECT (macvtap).

* src/qemu/qemu_conf.h: add vhostfd to qemuBuildHostNetStr prototype
  add qemudOpenVhostNet prototype new flag to set when :,vhost=" found in
  qemu help
* src/qemu/qemu_conf.c: * set QEMUD_CMD_FLAG_VNET_HOST is ",vhost=" found
  in qemu help
   - qemudOpenVhostNet - opens /dev/vhost-net to pass to qemu if everything
     is in place to use it.
   - qemuBuildHostNetStr - add vhostfd to commandline if it's not empty
     (higher levels decide whether or not to fill it in)
   - qemudBuildCommandLine - if /dev/vhost-net is successfully opened, add
     its fd to tapfds array so it isn't closed on qemu exec, and populate
     vhostfd_name to be passed in to commandline builder.
* src/qemu/qemu_driver.c: add filler 0 for new arg to qemuBuildHostNetStr,
  along with a note that this must be implemented in order for hot-plug of
  vhost-net virtio devices to work properly (once qemu "netdev_add" monitor
  command is implemented).

The logfile FD is dup2'ed in __virExec in the child. The FD needs to
be closed in the parent, otherwise it leaks.

Currently no command can be sent to a qemu process while another job is
active. This patch adds support for signaling long-running jobs (such as
migration) so that other threads may request predefined operations to be
done during such jobs. Two signals are defined so far:
    - QEMU_JOB_SIGNAL_CANCEL
    - QEMU_JOB_SIGNAL_SUSPEND

The first one is used by qemuDomainAbortJob.

The second one is used by qemudDomainSuspend for suspending a domain
during migration, which allows for changing live migration into offline
migration. However, there is a small issue in the way qemudDomainSuspend
is currently implemented for migrating domains. The API calls returns
immediately after signaling migration job which means it is asynchronous
in this specific case.
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>

* src/qemu/qemu_driver.c (qemudDomainAttachSCSIDisk): The ".controller"
member is an index, and *may* be 0.  As such, the commit that we're
reverting broke SCSI disk hot-plug on controller 0.
Reported by Wolfgang Mauerer.

We need to call PrepareHostdevs to determine the USB device path before
any security calls. PrepareHostUSBDevices was also incorrectly skipping
all USB devices.

Currently if you dump the core of a qemu guest with
qemudDomainCoreDump, subsequent commands will hang
up libvirtd.  This is because qemudDomainCoreDump
uses qemuDomainWaitForMigrationComplete, which expects
the qemuDriverLock to be held when it's called.  This
patch does the simple thing and moves the qemuDriveUnlock
to the end of the qemudDomainCoreDump so that the driver
lock is held for the entirety of the call (as it is done
in qemudDomainSave).  We will probably want to make the
lock more fine-grained than that in the future, but
we can fix both qemudDomainCoreDump and qemudDomainSave
at the same time.
Signed-off-by: NChris Lalancette <clalance@redhat.com>

The code to add job support into libvirtd caused a problem
in qemudDomainSetVcpus.  In particular, a qemuDomainObjEndJob()
call was added at the end of the function, but a
corresponding qemuDomainObjBeginJob() was not.  Additionally,
a call to qemuDomainObj{Enter,Exit}Monitor() was also missed
in qemudDomainHotplugVcpus().  These missing calls conspired to
cause a hang in the libvirtd process after the command was
finished.  Fix this by adding the missing calls.
Signed-off-by: NChris Lalancette <clalance@redhat.com>

As previously discussed[1], this patch removes the
qemudDomainSetMaxMemory() function, since it doesn't
work.  This means that instead of getting somewhat
cryptic errors, you will now get:

error: Unable to change MaxMemorySize
error: this function is not supported by the hypervisor: virDomainSetMaxMemory

Which describes the situation perfectly.

[1] https://www.redhat.com/archives/libvir-list/2010-February/msg00928.htmlSigned-off-by: NChris Lalancette <clalance@redhat.com>

* global: patch created by running:
for f in $(git ls-files '*.[ch]') ; do
    cppi $f > $f.t && mv $f.t $f
done

When adding domainMemoryStats API support for the qemu driver, I didn't
follow the locking rules exactly.  The job condition must be held when
executing monitor commands.  This corrects the segfaults I was seeing
when calling domainMemoryStats in a multi-threaded environment.

* src/qemu/qemu_driver.c: in qemudDomainMemoryStats() add missing
  calls to qemuDomainObjBeginJob/qemuDomainObjEndJob

doTunnelSendAll function (used by QEMU migration) uses a 64k buffer on
the stack, which could be problematic. This patch replaces that with a
buffer from the heap.

While in the neighborhood, this patch also improves error reporting in
the case that saferead fails - previously, virStreamAbort() was called
(resetting errno) before reporting the error. It's been changed to
report the error first.

* src/qemu/qemu_driver.c: fix doTunnelSendAll() to use a malloc'ed
  buffer

* src/qemu/qemu_driver.c (qemudDomainAttachSCSIDisk): Handle
the (theoretical) case of an empty controller list, so that
clang does not think the subsequent dereference of "cont"
would dereference an undefined variable (due to preceding
loop not iterating even once).

* src/qemu/qemu_driver.c (qemudDomainRestore): A corrupt save file
(in particular, a too-large header.xml_len value) would cause an
unwarranted out-of-memory error.  Do not trust the just-read
header.xml_len.  Instead, merely use that as a hint, and
read/allocate up to that number of bytes from the file.
Also verify that header.xml_len is positive; if it were negative,
passing it to virFileReadLimFD could cause trouble.

Changeset

  commit 5073aa99
  Author: Cole Robinson <crobinso@redhat.com>
  Date:   Mon Jan 11 11:40:46 2010 -0500

Added support for product/vendor based passthrough, but it only
worked at the security driver layer. The main guest XML config
was not updated with the resolved bus/device ID. When the QEMU
argv refactoring removed use of product/vendor, this then broke
launching guests.

THe solution is to move the product/vendor resolution up a layer
into the QEMU driver. So the first thing QEMU does is resolve
the product/vendor to a bus/device and updates the XML config
with this info. The rest of the code, including security drivers
and QEMU argv generated can now rely on bus/device always being
set.

* src/util/hostusb.c, src/util/hostusb.h: Split vendor/product
  resolution code out of usbGetDevice and into usbFindDevice.
  Add accessors for bus/device ID
* src/security/virt-aa-helper.c, src/security/security_selinux.c,
  src/qemu/qemu_security_dac.c: Remove vendor/product from the
  usbGetDevice() calls
* src/qemu/qemu_driver.c: Use usbFindDevice to resolve vendor/product
  into a bus/device ID

The pci_del command is not being ported to QMP. Convert all the
QEMU hotplug code over to use device_del whenever it is available
to avoid the pci_del problem

* src/qemu/qemu_driver.c: Convert unplug code to device_del

Previously hot-unplug could not be supported for USB devices
in QEMU, since usb_del required the guest visible address
which libvirt never knows. With 'device_del' command we can
now unplug based on device alias, so support that.

* src/qemu/qemu_driver.c: Use device_del to remove USB devices

QEMU has a monitor command 'set_cpu' which allows a specific
CPU to be toggled between online& offline state. libvirt CPU
hotplug does not work in terms of individual indexes CPUs.
Thus to support this, we iteratively toggle the online state
when the total number of vCPUs is adjusted via libvirt

NB, currently untested since QEMU segvs when running this!

* src/qemu/qemu_driver.c: Toggle online state for CPUs when
  doing hotplug
* src/qemu/qemu_monitor.c, src/qemu/qemu_monitor.h,
  src/qemu/qemu_monitor_json.c, src/qemu/qemu_monitor_json.h,
  src/qemu/qemu_monitor_text.c, src/qemu/qemu_monitor_text.h: Add
  monitor API for toggling a CPU's online status via 'set_cpu

The code to remove the cgroup after QEMU failed to startup could
be obscuring a real error from earlier on. It is not neccessary
to raise an error in this case, so tell cgroups to keep quiet

* src/qemu/qemu_driver.c: Don't raise cgroups error in QEMU start
  cleanup code.

The QEMU hotunplug code for PCI devices was looking at host
devices in the guest config without first filtering non
PCI devices. This means it was reading garbage

* src/qemu/qemu_driver.c: Filter out non-PCI devices

Commit 3c12a67b added
a dependency on the NFS_SUPER_MAGIC macro, which is
defined in linux/magic.h.  Unfortunately linux/magic.h
is not available in RHEL-5, and causes a compile error.
Just define it locally, since this is something that
can't change.
Signed-off-by: NChris Lalancette <clalance@redhat.com>

Move *all* file operations related to creation and writing of libvirt
header to the domain save file into a hook function that is called by
virFileOperation. First try to call virFileOperation as root. If that
fails with EACCESS, and (in the case of Linux) statfs says that we're
trying to save the file on an NFS share, rerun virFileOperation,
telling it to fork a child process and setuid to the qemu user. This
is the only way we can successfully create a file on a root-squashed
NFS server.

This patch (along with setting dynamic_ownership=0 in qemu.conf)
makes qemudDomainSave work on root-squashed NFS.

* src/qemu/qemu_driver.c: provide new qemudDomainSaveFileOpHook()
  utility, use it in qemudDomainSave() if normal creation of the
  file as root failed, and after checking the filesystem type for
  the storage is NFS. In that case we also bypass the security
  driver, as this would fail on NFS.

If qemudDomainRestore fails to open the domain save file, create a
pipe, then fork a process that does setuid(qemu_user) and opens the
file, then reads this file and stuffs it into the pipe. the parent
libvirtd process will use the other end of the pipe as its fd, then
reap the child process after it's done reading.

This makes domain restore work on a root-squash NFS share that is only
visible to the qemu user.

* src/qemu/qemu_driver.c: add new qemudOpenAsUID() helper function,
  and use it in qemudDomainRestore() if reading as root directly failed.

The USB/PCI device hotplug code for the QEMU driver was forgetting
to allocate a unique device alias.

* src/qemu/qemu_driver.c: Fill in device alias for USB/PCI devices

When a VM save attempt failed, the VM would be left in a paused
state. It is neccessary to resume CPU execution upon failure
if it was running originally

* src/qemu/qemu_driver.c: Resume CPUs upon save failure

This supports cancellation of jobs for the QEMU driver against
the virDomainMigrate, virDomainSave and virDomainCoreDump APIs.
It is not yet supported for the virDomainRestore API, although
it is desirable.

* src/qemu/qemu_driver.c: Issue 'migrate_cancel' command if
  virDomainAbortJob is issued during a migration operation
* tools/virsh.c: Add a domjobabort command