[libvirt] [PATCH v2] processSerialChangedEvent: Close agent monitor early

Martin Kletzander mkletzan at redhat.com
Thu May 7 14:07:05 UTC 2015

On Thu, May 07, 2015 at 11:33:58AM +0200, Michal Privoznik wrote:
>So, imagine you've issued an API that involves guest agent. For
>instance, you want to query guest's IP addresses. So the API acquires
>QUERY_JOB, locks the guest agent and issues the agent command.
>However, for some reason, guest agent replies to initial ping
>correctly, but then crashes tragically while executing real command
>(in this case guest-network-get-interfaces). Since initial ping went
>well, libvirt thinks guest agent is accessible and awaits reply to the
>real command. But it will never come. What will is a monitor event.
>Our handler (processSerialChangedEvent) will try to acquire
>MODIFY_JOB, which will fail obviously because the other thread that's
>executing the API already holds a job. So the event handler exits
>early, and the QUERY_JOB is never released nor ended.
>The way how to solve this is to put flag somewhere in the monitor
>internals. The flag is called @running and agent commands are issued
>iff the flag is set. The flag itself is set when we connect to the
>agent socket. And unset whenever we see DISCONNECT event from the
>agent. Moreover, we must wake up all the threads waiting for the
>agent. This is done by signalizing the condition they're waiting on.
>Signed-off-by: Michal Privoznik <mprivozn at redhat.com>

ACK, all of that is necessary and it also complies with the error
message flag request from v1.
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