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Re: [libvirt] [PATCH] qemu: turn on virtlockd by default



On Thu, Feb 02, 2017 at 10:02:54 +0000, Daniel Berrange wrote:
> On Thu, Feb 02, 2017 at 10:58:50AM +0100, Peter Krempa wrote:
> > On Wed, Feb 01, 2017 at 18:11:28 +0000, Daniel Berrange wrote:
> > > On Wed, Feb 01, 2017 at 07:04:54PM +0100, Peter Krempa wrote:
> > > > On Wed, Feb 01, 2017 at 16:54:01 +0000, Daniel Berrange wrote:

[..]

> > We can and we do, the problem is only if libvirt would not run at that
> > point, when it's hard to re-detect what's happening. We also don't track
> > which job we've started for non-active commit and block pull and thus
> > can't infer from the backing chain which was dropped.
> > 
> > > contain enough info to correlate back to libvirt's record of the job.
> > 
> > Well it won't be that hard to fix for the active case. We need to track
> > the backing chain fully anyways. The problem only remains in case when
> > we need to infer whether it was or wasn't successful if we missed the
> > event.
> > 
> > I've filed https://bugzilla.redhat.com/show_bug.cgi?id=1405537 a while
> > ago so that I don't forget about this issue.
> > 
> > I'm currently working on the support for blockdev-add and friends so
> > this work will be somewhat relevant to that. I'll let you know once all
> > known locking issues are resolved.
> 
> So based on the above we only have a show stopper problem if libvirtd
> is restarted while a job is running. IMHO if we can make job handling

Yes, if the block job finishes/fails while libvirtd is not running the
file will remain locked forever. I still consider that a serious problem
since you can't recover from that and the image stays locked.

The tracking of the block job is still required though and we don't do
that currently.

> reliable while libvirtd is running that is good enough to let us enable

Off topic: I'd rather not make "good enough" a sufficient measure for
adding stuff to libvirt ...

> virtlockd by default, without needing to wait for QEMU improvements.

Peter

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