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Date: Wed, 04 Jun 2014 11:04:24 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] block: asynchronously stop the VM on I/O
	errors
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To: Kevin Wolf <kwolf@redhat.com>
Cc: famz@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com

Il 04/06/2014 10:28, Kevin Wolf ha scritto:
>> Breaking this invariant means that you have a very small window where
>> {'execute':'cont'} would actually not restart the VM.  I think this
>> should be fixed by dropping the request in vm_start, like this:
>> [...]
>
> Sounds like an option. Do we need to send a QEVENT_STOP/QEVENT_RESUME
> pair? If we don't, the client will still notice a difference to a real
> stop and resume.

Yes, better do that.

>> Also, I think that bdrv_emit_qmp_error_event is placed wrong.
>> It should be called only after setting the iostatus, otherwise
>> there is a small window where the iostatus is "no error" but
>> the event has been generated already.
>
> Yes, I agree.
>
> The documentation for this event actually answers my above question:
>
>     Note: If action is "stop", a STOP event will eventually follow the
>     BLOCK_IO_ERROR event.
>
> Perhaps we should also change the documentation of the "stop" value to
> clarify that the VM may not actually be stopped yet. It currently reads
> like this:
>
>     "stop": error caused VM to be stopped

Yes.

Paolo