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Re: [Qemu-devel] active block commit bug?
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] active block commit bug? |
Date: |
Thu, 5 Jun 2014 11:07:49 +0800 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Wed, 06/04 20:55, Eric Blake wrote:
> On 06/04/2014 08:09 PM, Fam Zheng wrote:
>
> >> Sounds like we have an off-by-one condition if empty files behave
> >> differently from other files. We ought to fix that bug (not that your
> >> normal guest will ever have a 0-length backing file, but this was what I
> >> was trying to use for libvirt's probing of whether active commit is
> >> supported)
> >>
> >
> > Yes, agreed, this special case is only going to make management confused. I
> > will send a patch to fix this.
>
> Thanks.
>
> >
> > Eric, is this a good way to probe the active commit? I was expecting full
> > instrospection of QMP could do it, but I don't know about the status of that
> > piece of work. Amos, any ideas?
>
> Introspection already missed qemu 2.0 when active commit was added; and
> we're close enough to soft freeze for 2.1 that I'm guessing it will miss
> 2.1 as well :(
>
> So yes, I'm experimenting with how to learn if active commit works by
> seeing what error message differences I can trigger with minimum effort;
> libvirt will cache what it learns so that it only has to ask once per
> qemu binary/timestamp, then let the user know up front whether active
> commit will work. Since there are existing qemu versions that have
> active commit but not introspection, I'm stuck using this harder probe
> to avoid a false negative for those older qemu. My other option is to
> just wait for introspection, or even something intermediate like Jeff's
> patch to make 'top' optional, and just declare qemu 2.0 active commit as
> not working - but since it is only the special case of a 0-size file
> (which is fairly unlikely for any real client use, and certainly
> something I can avoid in the libvirt probing), it feels a bit harsh to
> reject 2.0 just for this corner-case bug.
>
Thanks, I'll keep in mind the feature probing necessity in the future.
Fam
- [Qemu-devel] active block commit bug?, Eric Blake, 2014/06/04
- Re: [Qemu-devel] active block commit bug?, Jeff Cody, 2014/06/04
- Re: [Qemu-devel] active block commit bug?, Eric Blake, 2014/06/04
- Re: [Qemu-devel] active block commit bug?, Fam Zheng, 2014/06/04
- Re: [Qemu-devel] active block commit bug?, Eric Blake, 2014/06/04
- Re: [Qemu-devel] active block commit bug?,
Fam Zheng <=
- Re: [Qemu-devel] active block commit bug?, Markus Armbruster, 2014/06/05
- Re: [Qemu-devel] active block commit bug?, Kevin Wolf, 2014/06/05
- Re: [Qemu-devel] active block commit bug?, Markus Armbruster, 2014/06/05
- Re: [Qemu-devel] active block commit bug?, Amos Kong, 2014/06/06