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Re: [Qemu-devel] [libvirt] virDomainBlockJobAbort and block_job_cancel

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] [libvirt] virDomainBlockJobAbort and block_job_cancel
Date: Thu, 8 Dec 2011 14:55:49 +0000

On Wed, Dec 7, 2011 at 11:01 PM, Eric Blake <address@hidden> wrote:
> On 12/07/2011 03:35 PM, Adam Litke wrote:
> 4) Ask Stefan to make the HMP monitor command synchronous, but only
> expose the JSON command as asynchronous.  After all, it is only HMP
> where we can't wait for an event.

QEMU cannot do async commands, even for HMP.  My QEMU patches used to
work because there is a broken async flag for monitor commands.  I
didn't know it was broken at the time O:-).

I have CCed Luiz who has been working on moving commands off the old
MONITOR_CMD_ASYNC flag.  My current understanding is that patches
adding use of MONITOR_CMD_ASYNC will not be accepted.

>> 2) Poll the qemu monitor
>> To do it this way, I would write a function that repeatedly calls
>> virDomainGetBlockJobInfo() against the disk in question.  Once the job
>> disappears from the list I can return with confidence that the job is gone.
>> This is obviously sub-optimal because I need to poll and sleep.
> We've done this before, for both HMP and JSON - see
> qemuMigrationWaitForCompletion.  I agree that an event is nicer than
> polling, but we may be locked into this.

This seems like the safest option although it's ugly.


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