1. 04 3月, 2014 29 次提交
    • C
      add 'driver' info to used_by · de6fa535
      Chunyan Liu 提交于
      Specify which driver and which domain in used_by area to avoid conflict among
      different drivers.
      Signed-off-by: NChunyan Liu <cyliu@suse.com>
      de6fa535
    • C
      apparmor: handle "none" type · 9194ccec
      Cédric Bosdonnat 提交于
      9194ccec
    • C
      add support for apparmor in lxc-enter-namespace · ef7dc7d4
      Cédric Bosdonnat 提交于
      ef7dc7d4
    • C
      apparmor: add debug traces when changing profile. · 500b2e96
      Cédric Bosdonnat 提交于
      The reason for these is that aa-status doesn't show the process using
      the profile as they are in another namespace.
      500b2e96
    • C
      Make sure apparmor is started before libvirtd · a3e4eeff
      Cédric Bosdonnat 提交于
      If apparmor security driver is enabled in either qemu or lxc
      driver configuration and libvirtd starts before AppArmor, it will fail.
      a3e4eeff
    • C
      LXC driver: generate apparmor profiles for guests · 43c030f0
      Cédric Bosdonnat 提交于
      use_apparmor() was first designed to be called from withing libvirtd,
      but libvirt_lxc also uses it. in libvirt_lxc, there is no need to check
      whether to use apparmor or not: just use it if possible.
      43c030f0
    • P
      qemu: monitor: Fix error message and comment when getting cpu info · a31bd18f
      Peter Krempa 提交于
      In qemuMonitorJSONExtractCPUInfo an error message hinted on missing
      character device data which is wrong.
      
      Also a comment states that only qemu-kvm tree includes the thread_id
      field. This is no longer true.
      a31bd18f
    • P
      qemu: snapshot: Use better check when reverting external snapshots · d410e6f1
      Peter Krempa 提交于
      https://bugzilla.redhat.com/show_bug.cgi?id=1071264
      
      Reverting of external snapshots is not supported currently. The check
      that is present doesn't properly check for all aspects that make a
      snapshot external. Use virDomainSnapshotIsExternal() to do the check.
      d410e6f1
    • M
      qemuBuildNicDevStr: Adapt to new advisory on multiqueue · 042c4ab1
      Michal Privoznik 提交于
      As I did previously in 4f588a1b, libvirt needs to set virtio vectors.
      Previously, we were advised to use vectors=N, where
      
      N = 2 * (number of queues) + 1
      
      However, just recently this advisory has changed on the Multiquue wiki
      page [1] to:
      
      N = 2 * (number of queues) + 2
      
      1: http://www.linux-kvm.org/page/Multiqueue#Enable_MQ_featureSigned-off-by: NMichal Privoznik <mprivozn@redhat.com>
      042c4ab1
    • J
      Check if systemd is running before creating machines · 12ee0b98
      Ján Tomko 提交于
      If systemd is installed, but is not the init system,
      systemd-machined fails with an unhelpful error message:
      Launch helper exited with unknown return code 1
      
      Currently we only check if the "machine1" service is
      available (in ListActivatableNames).
      Also check if "systemd1" service is registered with DBus
      (ListNames).
      
      This fixes https://bugs.gentoo.org/show_bug.cgi?id=493246#c22
      12ee0b98
    • J
      Split out most of virDBusIsServiceEnabled · 65a4cb03
      Ján Tomko 提交于
      Introduce virDBusIsServiceInList which can be used to call other
      methods for listing services (ListNames), not just ListActivatableNames.
      
      No functional change, fixed the 'Retruns' typo.
      65a4cb03
    • J
      Don't always skip virportallocatortest · d7e0f113
      Ján Tomko 提交于
      Include dlfcn.h before checking if RTLD_NEXT is defined
      d7e0f113
    • M
      tests: Create privileged driver config in qemuxml2argvtest · 29151830
      Martin Kletzander 提交于
      This is actually a proper setting since we're not checking
      session-mode related XMLs.
      Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>
      29151830
    • J
      build: Include sys/wait.h in commandtest.c · 460e42b1
      Ján Tomko 提交于
      Commit 631923e7 used a few macros from sys/wait.h without including
      it. On Linux, they were also defined in stdlib.h, but on FreeBSD
      the build failed:
      
      ../../tests/commandtest.c: In function 'test1':
      warning: implicit declaration of function 'WIFEXITED'
      warning: nested extern declaration of 'WIFEXITED' [-Wnested-externs]
      460e42b1
    • E
      build: fix cppi warning · b75c7bd6
      Eric Blake 提交于
      Jenkins pointed out that the previous commit violates syntax
      check when cppi is installed.
      
      * src/nwfilter/nwfilter_dhcpsnoop.c (SNOOP_POLL_MAX_TIMEOUT_MS):
      Update indentation.
      Signed-off-by: NEric Blake <eblake@redhat.com>
      b75c7bd6
    • S
      nwfilter: Increase buffer size for libpcap · 49b59a15
      Stefan Berger 提交于
      Libpcap 1.5 requires a larger buffer than previous pcap versions.
      Adjust the size of the buffer to 128kb.
      
      This patch should address symptoms in BZ 1071181 and BZ 731059
      Signed-off-by: NStefan Berger <stefanb@linux.vnet.ibm.com>
      49b59a15
    • S
      nwfilter: Display the pcap errror message · 64df4c75
      Stefan Berger 提交于
      Display the pcap error message in the log.
      Signed-off-by: NStefan Berger <stefanb@linux.vnet.ibm.com>
      64df4c75
    • S
      nwfilter: Cap the poll timeout in the DHCP Snooping code · a718eb19
      Stefan Berger 提交于
      Cap the poll timeout in the DHCP Snooping code to a max. of 10 seconds
      to not hold up the libvirt shutdown longer than this.
      Signed-off-by: NStefan Berger <stefanb@linux.vnet.ibm.com>
      a718eb19
    • E
      virsh: report exit status of failed lxc-enter-namespace · 2ebf593a
      Eric Blake 提交于
      'virsh lxc-enter-namespace' does not have a way to reflect exit
      status to the caller in single-command mode, but we might as well
      at least report the exit status.  Prior to this patch,
      
      $ virsh -c lxc:/// lxc-enter-namespace shell /bin/sh 'exit 3'; echo $?
      1
      
      now it gives some details:
      
      $ virsh -c lxc:/// lxc-enter-namespace shell /bin/sh -c 'exit 3'; echo $?
      error: internal error: Child process (31557) unexpected exit status 3
      1
      
      Also useful:
      
      $ virsh -c lxc:/// lxc-enter-namespace shell /bin/sh -c 'kill $$'; echo $?
      error: internal error: Child process (31585) unexpected fatal signal 15
      1
      
      * tools/virsh-domain.c (cmdLxcEnterNamespace): Avoid magic numbers.
      Dispatch any error.
      * tools/virsh.pod: Document that non-zero exit status is collapsed.
      Signed-off-by: NEric Blake <eblake@redhat.com>
      2ebf593a
    • E
      virt-login-shell: saner exit value · 730fc962
      Eric Blake 提交于
      virt-login-shell was exiting with status 0, regardless of what the
      wrapped shell returned.  This is unkind to users; we should behave
      more like env(1), nice(1), su(1), and other wrapper programs, by
      preserving the invoked application's status (which includes the
      distinction between death due to signal vs. normal death).
      
      * tools/virt-login-shell.c (main): Pass through child exit status.
      * tools/virt-login-shell.pod: Document exit status.
      Signed-off-by: NEric Blake <eblake@redhat.com>
      730fc962
    • E
      virt-login-shell: use single instead of double fork · 4594a33b
      Eric Blake 提交于
      Note that 'virsh lxc-enter-namespace' must double-fork, for two
      reasons: some namespaces can only be done from a single thread,
      while virsh is multithreaded; and because virsh can be run in
      batch mode where we must not corrupt the namespace of that
      execution upon return from the subsidiary command.
      
      When virt-login-shell was first written, it blindly copied from
      'virsh lxc-enter-namespace', including the double-fork.  But
      neither of the reasons for double forking apply to
      virt-login-shell (we are single-threaded, and we have nothing to
      do after the child completes that would require us to preserve a
      namespace), so we can simplify life by using a single fork.
      In turn, this will make it easier for a future patch to pass the
      child's exit status on to the invoking shell.
      
      In flattening to a single fork, note that closing the fds must
      be done after fork, because the parent process still needs to
      use fds to control the virConnectPtr; meanwhile, chdir can be
      done prior to forking (in fact, it's easier to report errors
      on anything attempted before forking).
      
      * tools/virt-login-shell.c (main): Single rather than double fork.
      (virLoginShellFini): Delete, by inlining actions instead.
      Signed-off-by: NEric Blake <eblake@redhat.com>
      4594a33b
    • E
      virFork: simplify semantics · 25f87817
      Eric Blake 提交于
      The old semantics of virFork() violates the priciple of good
      usability: it requires the caller to check the pid argument
      after use, *even when virFork returned -1*, in order to properly
      abort a child process that failed setup done immediately after
      fork() - that is, the caller must call _exit() in the child.
      While uses in virfile.c did this correctly, uses in 'virsh
      lxc-enter-namespace' and 'virt-login-shell' would happily return
      from the calling function in both the child and the parent,
      leading to very confusing results. [Thankfully, I found the
      problem by inspection, and can't actually trigger the double
      return on error without an LD_PRELOAD library.]
      
      It is much better if the semantics of virFork are impossible
      to abuse.  Looking at virFork(), the parent could only ever
      return -1 with a non-negative pid if it misused pthread_sigmask,
      but this never happens.  Up until this patch series, the child
      could return -1 with non-negative pid if it fails to set up
      signals correctly, but we recently fixed that to make the child
      call _exit() at that point instead of forcing the caller to do
      it.  Thus, the return value and contents of the pid argument are
      now redundant (a -1 return now happens only for failure to fork,
      a child 0 return only happens for a successful 0 pid, and a
      parent 0 return only happens for a successful non-zero pid),
      so we might as well return the pid directly rather than an
      integer of whether it succeeded or failed; this is also good
      from the interface design perspective as users are already
      familiar with fork() semantics.
      
      One last change in this patch: before returning the pid directly,
      I found cases where using virProcessWait unconditionally on a
      cleanup path of a virFork's -1 pid return would be nicer if there
      were a way to avoid it overwriting an earlier message.  While
      such paths are a bit harder to come by with my change to a direct
      pid return, I decided to keep the virProcessWait change in this
      patch.
      
      * src/util/vircommand.h (virFork): Change signature.
      * src/util/vircommand.c (virFork): Guarantee that child will only
      return on success, to simplify callers.  Return pid rather than
      status, now that the situations are always the same.
      (virExec): Adjust caller, also avoid open-coding process death.
      * src/util/virprocess.c (virProcessWait): Tweak semantics when pid
      is -1.
      (virProcessRunInMountNamespace): Adjust caller.
      * src/util/virfile.c (virFileAccessibleAs, virFileOpenForked)
      (virDirCreate): Likewise.
      * tools/virt-login-shell.c (main): Likewise.
      * tools/virsh-domain.c (cmdLxcEnterNamespace): Likewise.
      * tests/commandtest.c (test23): Likewise.
      Signed-off-by: NEric Blake <eblake@redhat.com>
      25f87817
    • E
      util: make it easier to grab only regular command exit · b9dd878f
      Eric Blake 提交于
      Auditing all callers of virCommandRun and virCommandWait that
      passed a non-NULL pointer for exit status turned up some
      interesting observations.  Many callers were merely passing
      a pointer to avoid the overall command dying, but without
      caring what the exit status was - but these callers would
      be better off treating a child death by signal as an abnormal
      exit.  Other callers were actually acting on the status, but
      not all of them remembered to filter by WIFEXITED and convert
      with WEXITSTATUS; depending on the platform, this can result
      in a status being reported as 256 times too big.  And among
      those that correctly parse the output, it gets rather verbose.
      Finally, there were the callers that explicitly checked that
      the status was 0, and gave their own message, but with fewer
      details than what virCommand gives for free.
      
      So the best idea is to move the complexity out of callers and
      into virCommand - by default, we return the actual exit status
      already cleaned through WEXITSTATUS and treat signals as a
      failed command; but the few callers that care can ask for raw
      status and act on it themselves.
      
      * src/util/vircommand.h (virCommandRawStatus): New prototype.
      * src/libvirt_private.syms (util/command.h): Export it.
      * docs/internals/command.html.in: Document it.
      * src/util/vircommand.c (virCommandRawStatus): New function.
      (virCommandWait): Adjust semantics.
      * tests/commandtest.c (test1): Test it.
      * daemon/remote.c (remoteDispatchAuthPolkit): Adjust callers.
      * src/access/viraccessdriverpolkit.c (virAccessDriverPolkitCheck):
      Likewise.
      * src/fdstream.c (virFDStreamCloseInt): Likewise.
      * src/lxc/lxc_process.c (virLXCProcessStart): Likewise.
      * src/qemu/qemu_command.c (qemuCreateInBridgePortWithHelper):
      Likewise.
      * src/xen/xen_driver.c (xenUnifiedXendProbe): Simplify.
      * tests/reconnect.c (mymain): Likewise.
      * tests/statstest.c (mymain): Likewise.
      * src/bhyve/bhyve_process.c (virBhyveProcessStart)
      (virBhyveProcessStop): Don't overwrite virCommand error.
      * src/libvirt.c (virConnectAuthGainPolkit): Likewise.
      * src/openvz/openvz_driver.c (openvzDomainGetBarrierLimit)
      (openvzDomainSetBarrierLimit): Likewise.
      * src/util/virebtables.c (virEbTablesOnceInit): Likewise.
      * src/util/viriptables.c (virIpTablesOnceInit): Likewise.
      * src/util/virnetdevveth.c (virNetDevVethCreate): Fix debug
      message.
      * src/qemu/qemu_capabilities.c (virQEMUCapsInitQMP): Add comment.
      * src/storage/storage_backend_iscsi.c
      (virStorageBackendISCSINodeUpdate): Likewise.
      Signed-off-by: NEric Blake <eblake@redhat.com>
      b9dd878f
    • E
      util: make it easier to grab only regular process exit · c72e76c3
      Eric Blake 提交于
      Right now, a caller waiting for a child process either requires
      the child to have status 0, or must use WIFEXITED() and friends
      itself.  But in many cases, we want the middle ground of treating
      fatal signals as an error, and directly accessing the normal exit
      value without having to use WEXITSTATUS(), in order to easily
      detect an expected non-zero exit status.  This adds the middle
      ground to the low-level virProcessWait; the next patch will add
      it to virCommand.
      
      * src/util/virprocess.h (virProcessWait): Alter signature.
      * src/util/virprocess.c (virProcessWait): Add parameter.
      (virProcessRunInMountNamespace): Adjust caller.
      * src/util/vircommand.c (virCommandWait): Likewise.
      * src/util/virfile.c (virFileAccessibleAs): Likewise.
      * src/lxc/lxc_container.c (lxcContainerHasReboot)
      (lxcContainerAvailable): Likewise.
      * daemon/libvirtd.c (daemonForkIntoBackground): Likewise.
      * tools/virt-login-shell.c (main): Likewise.
      * tools/virsh-domain.c (cmdLxcEnterNamespace): Likewise.
      * tests/testutils.c (virtTestCaptureProgramOutput): Likewise.
      * tests/commandtest.c (test23): Likewise.
      Signed-off-by: NEric Blake <eblake@redhat.com>
      c72e76c3
    • E
      util: preserve exit status from mount namespace callback · 8b24a803
      Eric Blake 提交于
      The documentation of namespace callbacks was inconsistent on whether
      it preserved positive return values.  Now that we have a dedicated
      EXIT_CANCELED to flag all errors before getting to the callback,
      it is possible to use positive return values (not that any of the
      current callers do, but it is better to match the docs).
      
      Also, while vircommand.c is careful to close fds that a child should
      not have, it's still better to be in the practice of setting
      FD_CLOEXEC up front.
      
      * src/util/virprocess.c (virProcessRunInMountNamespace): Tweak
      return value to pass back non-zero status.  Avoid leaking pipe fds
      to other threads.
      * src/util/virprocess.h: Fix comment.
      Signed-off-by: NEric Blake <eblake@redhat.com>
      8b24a803
    • E
      util: make it easier to reflect child exit status · 2b4f162e
      Eric Blake 提交于
      Thanks to namespaces, we have a couple of places in the code
      base that want to reflect a child exit status, including the
      ability to detect death by a signal, back to a grandparent.
      Best to make it a reusable function.
      
      * src/util/virprocess.h (virProcessExitWithStatus): New prototype.
      * src/libvirt_private.syms (util/virprocess.h): Export it.
      * src/util/virprocess.c (virProcessExitWithStatus): New function.
      * tests/commandtest.c (test23): Test it.
      Signed-off-by: NEric Blake <eblake@redhat.com>
      2b4f162e
    • E
      virFork: give specific status on failure prior to exec · 631923e7
      Eric Blake 提交于
      When a child fails without exec'ing, we want a well-known status;
      best is to match what env(1), nice(1), su(1), and other wrapper
      programs do.  This patch adds enum values that later patches will
      use, and sets up virFork as the first client of EXIT_CANCELED
      for errors detected prior to even attempting exec, as well as
      virExec to distinguish between a missing executable vs. a binary
      that cannot be executed.
      
      This is a slight semantic change in the unlikely case of a child
      process failing to restore its signal mask - we now kill the
      child with a known status instead of relying on the caller to
      notice and do an appropriate _exit().  A subsequent patch will
      make further cleanups based on an audit of all callers.
      
      * src/internal.h (EXIT_CANCELED, EXIT_CANNOT_INVOKE)
      (EXIT_ENOENT): New enum.
      * src/util/vircommand.c (virFork): Document specific exit value if
      child aborts early.
      (virExec): Distinguish between various exec failures.
      * tests/commandtest.c (test1): Enhance test.
      (test22): New test.
      Signed-off-by: NEric Blake <eblake@redhat.com>
      631923e7
    • E
      nwfilter: make ignoring non-zero status easier to follow · f972a7c7
      Eric Blake 提交于
      While auditing all callers of virCommandRun, I noticed that nwfilter
      code never paid attention to commands with a non-zero status; they
      were merely passing a pointer to avoid spamming the logs with a
      message about commands that might indeed fail.  But proving this
      required chasing through a lot of code; refactoring things to
      localize the decision of whether to ignore non-zero status makes
      it easier to prove that later changes to virFork don't negatively
      affect this code.
      
      While at it, I also noticed that ebiptablesRemoveRules would
      actually report success if the child process failed for a
      reason other than non-zero status, such as OOM.
      
      * src/nwfilter/nwfilter_ebiptables_driver.c (ebiptablesExecCLI):
      Change parameter from pointer to bool.
      (ebtablesApplyBasicRules, ebtablesApplyDHCPOnlyRules)
      (ebtablesApplyDropAllRules, ebtablesCleanAll)
      (ebiptablesApplyNewRules, ebiptablesTearNewRules)
      (ebiptablesTearOldRules, ebiptablesAllTeardown)
      (ebiptablesDriverInitWithFirewallD)
      (ebiptablesDriverTestCLITools, ebiptablesDriverProbeStateMatch):
      Adjust all clients.
      (ebiptablesRemoveRules): Likewise, and fix return value on failure.
      Signed-off-by: NEric Blake <eblake@redhat.com>
      f972a7c7
    • O
      qemu: Implement a stub cpuArchDriver.baseline() handler for arm · 72bddd5f
      Oleg Strikov 提交于
      Openstack Nova calls virConnectBaselineCPU() during initialization
      of the instance to get a full list of CPU features.
      This patch adds a stub to arm-specific code to handle
      this request (no actual work is done).
      Signed-off-by: NOleg Strikov <oleg.strikov@canonical.com>
      72bddd5f
  2. 03 3月, 2014 7 次提交
    • R
      docs: typo fix · da78406e
      Roman Bogorodskiy 提交于
       * drvuml.html.in: (connected) s/toa PTY/to a PTY/
      da78406e
    • J
      Fix indentation in virsystemdmock · 93e721c6
      Ján Tomko 提交于
      93e721c6
    • J
      Replace space with a tab in the Makefile · a0936288
      Ján Tomko 提交于
      All the other test_programs in the section use tabs
      and virportallocatortest sticks out with tab width
      other than 8.
      a0936288
    • J
      Add a test for virUSBDeviceList functions · 295c1b0a
      Ján Tomko 提交于
      Most of them are already tested in a limited way
      by testing virUSBDeviceFind.
      295c1b0a
    • J
      Add tests for virUSBDeviceFind functions · 855e9faa
      Ján Tomko 提交于
      Mock the /sys/bus/usb directory and test the finding
      (and not finding) of some USB devices.
      855e9faa
    • D
      Generate a unique journald log for QEMU capabilities failure · 36ff4ed1
      Daniel P. Berrange 提交于
      When probing QEMU capabilities fails for a binary generate a
      log message with MESSAGE_ID==8ae2f3fb-2dbe-498e-8fbd-012d40afa361.
      
      This can be directly queried from journald based on the UUID
      instead of needing string grep. This lets tools like libguestfs'
      bug reporting tool trivially do automated sanity tests on the
      host they're running on.
      
       $ journalctl MESSAGE_ID=8ae2f3fb-2dbe-498e-8fbd-012d40afa361
       Feb 21 17:11:01 localhost.localdomain lt-libvirtd[9196]:
       Failed to probe capabilities for /bin/qemu-system-alpha:
       internal error: Child process (LC_ALL=C LD_LIBRARY_PATH=
       /home/berrange/src/virt/libvirt/src/.libs PATH=/usr/lib64/
       ccache:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:
       /usr/bin:/root/bin HOME=/root USER=root LOGNAME=root
       /bin/qemu-system-alpha -help) unexpected exit status 127:
       /bin/qemu-system-alpha: error while loading shared libraries:
       libglapi.so.0: cannot open shared object file: No such file
       or directory
      
       $ journalctl MESSAGE_ID=8ae2f3fb-2dbe-498e-8fbd-012d40afa361 --output=json
       { ...snip...
        "LIBVIRT_SOURCE" : "file",
        "PRIORITY" : "3",
        "CODE_FILE" : "qemu/qemu_capabilities.c",
        "CODE_LINE" : "2770",
        "CODE_FUNC" : "virQEMUCapsLogProbeFailure",
        "MESSAGE_ID" : "8ae2f3fb-2dbe-498e-8fbd-012d40afa361",
        "LIBVIRT_QEMU_BINARY" : "/bin/qemu-system-xtensa",
        "MESSAGE" : "Failed to probe capabilities for /bin/qemu-system-xtensa:
         internal error: Child process (LC_ALL=C LD_LIBRARY_PATH=/home/berrange
         /src/virt/libvirt/src/.libs PATH=/usr/lib64/ccache:/usr/local/sbin:
         /usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin HOME=/root
         USER=root LOGNAME=root /bin/qemu-system-xtensa -help) unexpected
         exit status 127: /bin/qemu-system-xtensa: error while loading shared
         libraries: libglapi.so.0: cannot open shared object file: No such
          file or directory\n" }
      Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>
      36ff4ed1
    • M
      Bump version to 1.2.3 for new dev cycle · 852582ea
      Michal Privoznik 提交于
      Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
      852582ea
  3. 02 3月, 2014 2 次提交
  4. 01 3月, 2014 2 次提交
    • R
      bhyve: defined domains should be persistent · ae49a093
      Roman Bogorodskiy 提交于
      ae49a093
    • E
      virsh: add --all flag to 'event' command · 0e16ae40
      Eric Blake 提交于
      Similar to our event-test demo program, it's nice to be able to
      have a mode where we can sniff all events at once, rather than
      having to spawn multiple virsh in parallel with one for each
      event type.
      
      (Can I just say our RegisterAny design is lousy?  The fact that
      the majority of our callback pointers have a function signature
      with the opaque data in a different position, and that we have
      to cast the function signature before registering it, makes it
      hard to write a generic callback function; we have to write one
      for every type of event id.  Life would have been easier if we
      had designed the callback as a fixed signature with a void*
      and size parameter, and then allowed the caller to downcast
      the void* to a particular struct for data specific to their
      callback id, where we could have then had a single function
      with a switch statement for each event id, and register that
      one function for all types of events.  It would also be nicer
      if the callback functions knew which callbackID was being used
      when invoking that callback, so that I could use a common data
      structure among all registrations instead of having to create
      an array of one data per callback.  But I really don't want to
      go add yet another event API design.)
      
      * tools/virsh-domain.c (cmdEvent): Add --all parameter; convert
      all callbacks to support shared counter.
      * tools/virsh.pod (event): Document it.
      Signed-off-by: NEric Blake <eblake@redhat.com>
      0e16ae40