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Bug#1120389: qemu: Deleting snapshot results in unexpected disk usage when detect-zeroes=off

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On Sat, Nov 15, 2025 at 01:40:51AM +0300, Michael Tokarev wrote:
> On 11/15/25 01:28, Michael Tokarev wrote:
> > I'm not familiar with libvirt.  Can you tell me what's the
> > equivalent actions with plain qemu, without libvirt, - how
> > to reproduce it with qemu?
> > 
> > Or maybe you can do a bisect between 10.0.0 and 10.1.0 and find
> > out which commit fixed it?
> 
> I think the fix is 6f3199f99600fe75f32f78574e507f347de80854
> "block: allow commit to unmap zero blocks" which talks about
> exactly the same situation --
> https://gitlab.com/qemu-project/qemu/-/commit/6f3199f99600fe75f32f78574e507f347de80854
> 
> (and a subsequent test for this as well).
> 
> It would be nice to have an easier reproducer still, to verify
> this.  Maybe the test would do.

Yeah that looks like a very plausible candidate. I can build the
trixie package with that commit on top and check whether it's enough
to make the issue go away. I'll report back within a few days.

-- 
Andrea Bolognani <eof@kiyuko.org>
Resistance is futile, you will be garbage collected.

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Bug#1120389: libvirt-daemon: libvirt disables detect_zeroes, resulting in denial of service during blockcommit/snapshot-delete zrm <debbug@trustiosity.com> - 2025-11-08 18:30 +0100
  Bug#1120389: qemu: Deleting snapshot results in unexpected disk usage when detect-zeroes=off (Was: Re: Bug#1120389: libvirt-daemon: libvirt disables detect_zeroes, resulting in denial of service during blockcommit/snapshot-delete) Andrea Bolognani <eof@kiyuko.org> - 2025-11-14 00:00 +0100
    Bug#1120389: qemu: Deleting snapshot results in unexpected disk usage when detect-zeroes=off (Was: Re: Bug#1120389: libvirt-daemon: libvirt disables detect_zeroes, resulting in denial of service during blockcommit/snapshot-delete) zrm <debbug@trustiosity.com> - 2025-11-14 08:50 +0100
      Bug#1120389: qemu: Deleting snapshot results in unexpected disk usage when detect-zeroes=off (Was: Re: Bug#1120389: libvirt-daemon: libvirt disables detect_zeroes, resulting in denial of service during blockcommit/snapshot-delete) Andrea Bolognani <eof@kiyuko.org> - 2025-11-14 22:50 +0100
        Bug#1120389: qemu: Deleting snapshot results in unexpected disk usage when detect-zeroes=off (Was: Re: Bug#1120389: libvirt-daemon: libvirt disables detect_zeroes, resulting in denial of service during blockcommit/snapshot-delete) Andrea Bolognani <eof@kiyuko.org> - 2025-11-20 23:50 +0100
  Bug#1120389: Processed: fixing versions Andrea Bolognani <eof@kiyuko.org> - 2025-11-14 23:20 +0100
  Bug#1120389: qemu: Deleting snapshot results in unexpected disk usage when detect-zeroes=off Andrea Bolognani <eof@kiyuko.org> - 2025-11-15 01:50 +0100
  Bug#1120389: qemu: Deleting snapshot results in unexpected disk usage when detect-zeroes=off Andrea Bolognani <eof@kiyuko.org> - 2025-11-26 01:30 +0100

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