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Re: [Qemu-devel] [PATCH] block: asynchronously stop the VM on I/O errors


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH] block: asynchronously stop the VM on I/O errors
Date: Wed, 04 Jun 2014 11:04:24 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0

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




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