[libvirt] [PATCH v2] qemu: agent: Avoid agentError when closing the QEMU agent

[Michal Privoznik]

On 09/28/2018 11:36 AM, Wang Yechao wrote:
> After calling qemuAgentClose(), it is still possible for
> the QEMU Agent I/O event callback to get invoked. This
> will trigger an agent error because mon->fd has been set
> to -1 at this point.  Then vm->privateData->agentError is
> always 'true' except that restart libvirtd or restart
> qemu-guest-agent process in guest.
> 
> Silently ignore the case where mon->fd is -1, likewise for
> mon->watch being zero.
> 
> Signed-off-by: Wang Yechao <wang.yechao255 at zte.com.cn>
> ---
> v1 patch:
> https://www.redhat.com/archives/libvir-list/2018-September/msg01382.html
> 
> Changes in v2:
>  - do not set agentError, let agent state as disconnected instead of error.
> ---
>  src/qemu/qemu_agent.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/src/qemu/qemu_agent.c b/src/qemu/qemu_agent.c
> index 97ad0e7..d842b0e 100644
> --- a/src/qemu/qemu_agent.c
> +++ b/src/qemu/qemu_agent.c
> @@ -530,6 +530,9 @@ static void qemuAgentUpdateWatch(qemuAgentPtr mon)
>          VIR_EVENT_HANDLE_HANGUP |
>          VIR_EVENT_HANDLE_ERROR;
>  
> +    if (!mon->watch)
> +        return;
> +
>      if (mon->lastError.code == VIR_ERR_OK) {
>          events |= VIR_EVENT_HANDLE_READABLE;
>  
> @@ -555,6 +558,12 @@ qemuAgentIO(int watch, int fd, int events, void *opaque)
>      VIR_DEBUG("Agent %p I/O on watch %d fd %d events %d", mon, watch, fd, events);
>  #endif
>  
> +    if (mon->fd == -1 || mon->watch == 0) {
> +        virObjectUnlock(mon);
> +        virObjectUnref(mon);
> +        return;
> +    }
> +

Is this safe to do? What if there's a thread waiting for a message from
the agent? Shouldn't @eof variable be set in this case so that
appropriate code is run?

>      if (mon->fd != fd || mon->watch != watch) {
>          if (events & (VIR_EVENT_HANDLE_HANGUP | VIR_EVENT_HANDLE_ERROR))
>              eof = true;
> @@ -788,8 +797,10 @@ void qemuAgentClose(qemuAgentPtr mon)
>      virObjectLock(mon);
>  
>      if (mon->fd >= 0) {
> -        if (mon->watch)
> +        if (mon->watch) {
>              virEventRemoveHandle(mon->watch);
> +            mon->watch = 0;
> +        }
>          VIR_FORCE_CLOSE(mon->fd);
>      }
>  
> 

Michal