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Re: [libvirt] [PATCH] Ignore qemu STOP event when stopping CPUs



On Tue, Apr 27, 2010 at 11:20:39AM +0200, jdenemar redhat com wrote:
> From: Jiri Denemark <jdenemar redhat com>
> 
> With JSON qemu monitor, we get a STOP event from qemu whenever qemu
> stops guests CPUs. The downside of it is that vm->state is changed to
> PAUSED and a new generic paused event is send to applications. However,
> when we ask qemu to stop the CPUs we are not really interested in qemu
> event and we usually want to issue a more specific event.
> 
> By setting vm->status to PAUSED before actually sending the request to
> qemu (and resetting it back if the request fails) we can ignore the
> event since the event handler does nothing when the guest is already
> paused. This solution is quite hacky but unfortunately it's the best
> solution which I was able to come up with and it doesn't introduce a
> race condition.
> ---
>  src/qemu/qemu_driver.c |   25 +++++++++++++++++++------
>  1 files changed, 19 insertions(+), 6 deletions(-)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 3c4876e..8ccf0b7 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -4117,13 +4117,16 @@ static int qemudDomainSuspend(virDomainPtr dom) {
>          }
>          if (vm->state != VIR_DOMAIN_PAUSED) {
>              int rc;
> +            int state = vm->state;
>  
> +            vm->state = VIR_DOMAIN_PAUSED;
>              qemuDomainObjEnterMonitorWithDriver(driver, vm);
>              rc = qemuMonitorStopCPUs(priv->mon);
>              qemuDomainObjExitMonitorWithDriver(driver, vm);
> -            if (rc < 0)
> +            if (rc < 0) {
> +                vm->state = state;
>                  goto endjob;
> -            vm->state = VIR_DOMAIN_PAUSED;
> +            }
>              event = virDomainEventNewFromObj(vm,
>                                               VIR_DOMAIN_EVENT_SUSPENDED,
>                                               VIR_DOMAIN_EVENT_SUSPENDED_PAUSED);
> @@ -4491,8 +4494,10 @@ qemuDomainMigrateOffline(struct qemud_driver *driver,
>                           virDomainObjPtr vm)
>  {
>      qemuDomainObjPrivatePtr priv = vm->privateData;
> +    int state = vm->state;
>      int ret;
>  
> +    vm->state = VIR_DOMAIN_PAUSED;
>      qemuDomainObjEnterMonitorWithDriver(driver, vm);
>      ret = qemuMonitorStopCPUs(priv->mon);
>      qemuDomainObjExitMonitorWithDriver(driver, vm);
> @@ -4500,13 +4505,13 @@ qemuDomainMigrateOffline(struct qemud_driver *driver,
>      if (ret == 0) {
>          virDomainEventPtr event;
>  
> -        vm->state = VIR_DOMAIN_PAUSED;
>          event = virDomainEventNewFromObj(vm,
>                                           VIR_DOMAIN_EVENT_SUSPENDED,
>                                           VIR_DOMAIN_EVENT_SUSPENDED_MIGRATED);
>          if (event)
>              qemuDomainEventQueue(driver, event);
> -    }
> +    } else
> +        vm->state = state;
>  
>      return ret;
>  }
> @@ -4743,13 +4748,14 @@ static int qemudDomainSaveFlag(virDomainPtr dom, const char *path,
>      /* Pause */
>      if (vm->state == VIR_DOMAIN_RUNNING) {
>          header.was_running = 1;
> +        vm->state = VIR_DOMAIN_PAUSED;
>          qemuDomainObjEnterMonitorWithDriver(driver, vm);
>          if (qemuMonitorStopCPUs(priv->mon) < 0) {
>              qemuDomainObjExitMonitorWithDriver(driver, vm);
> +            vm->state = VIR_DOMAIN_RUNNING;
>              goto endjob;
>          }
>          qemuDomainObjExitMonitorWithDriver(driver, vm);
> -        vm->state = VIR_DOMAIN_PAUSED;
>      }
>  
>      /* Get XML for the domain */
> @@ -5167,9 +5173,11 @@ static int qemudDomainCoreDump(virDomainPtr dom,
>  
>      /* Pause domain for non-live dump */
>      if (!(flags & VIR_DUMP_LIVE) && vm->state == VIR_DOMAIN_RUNNING) {
> +        vm->state = VIR_DOMAIN_PAUSED;
>          qemuDomainObjEnterMonitorWithDriver(driver, vm);
>          if (qemuMonitorStopCPUs(priv->mon) < 0) {
>              qemuDomainObjExitMonitorWithDriver(driver, vm);
> +            vm->state = VIR_DOMAIN_RUNNING;
>              goto endjob;
>          }
>          qemuDomainObjExitMonitorWithDriver(driver, vm);
> @@ -5214,6 +5222,7 @@ endjob:
>                                  "%s", _("resuming after dump failed"));
>          }
>          qemuDomainObjExitMonitorWithDriver(driver, vm);
> +        vm->state = VIR_DOMAIN_RUNNING;
>      }
>  
>      if (qemuDomainObjEndJob(vm) == 0)
> @@ -11056,12 +11065,16 @@ static int qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
>              /* qemu unconditionally starts the domain running again after
>               * loadvm, so let's pause it to keep consistency
>               */
> +            int state = vm->state;
>              priv = vm->privateData;
> +            vm->state = VIR_DOMAIN_PAUSED;
>              qemuDomainObjEnterMonitorWithDriver(driver, vm);
>              rc = qemuMonitorStopCPUs(priv->mon);
>              qemuDomainObjExitMonitorWithDriver(driver, vm);
> -            if (rc < 0)
> +            if (rc < 0) {
> +                vm->state = state;
>                  goto cleanup;
> +            }
>          }
>  
>          event = virDomainEventNewFromObj(vm,

  Hum, that sounds reasonnable, yes. All those operations should already
emit a more specific event, if that's the case, ACK.

Daniel

-- 
Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/


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