On 06/04/2014 06:12 PM, Jeff Cody wrote: >> Huh? I thought that an active commit was not supposed to complete >> automatically, but that the job would remain around until I either >> 'block-job-cancel' or 'block-job-complete' it. That is, I should have >> gotten a BLOCK_JOB_READY event and still see the job when I query for >> it. Where am I going wrong, or did I uncover a bug in active commit? >> > > I tried repeating your findings, but I couldn't, until I noticed that > 'f' was just a 0-length raw image in your test. > > The snapshot file will be the same size, 0. So when we go to perform > the active commit, we short-circuit at the beginning, since we are > committing a zero-length image:
That explains it.
>
> s->common.len = bdrv_getlength(bs);
> if (s->common.len <= 0) {
> block_job_completed(&s->common, s->common.len);
> return;
> }
> ^^^^^
> we exit early here, with a completed message, since there is
> nothing to do.
>
> If 'g' had increased to non-zero size, then you would have received a
> BLOCK_JOB_READY instead.
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)
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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