Ori Bernstein <o...@eigenstate.org> writes:

> Yep. I can look at it in a few days.
>
> I'm assuming that the vm was stopped before running the check?
>

Yes.

> On April 18, 2022 3:42:50 PM EDT, Mike Larkin <mlar...@nested.page> wrote:
>
>  On Mon, Apr 18, 2022 at 12:21:39PM -0400, Dave Voutila wrote:
>
>   "Thomas L." <tom.longsh...@web.de> writes:
>
>   Hi,
>
>  I recently tried to use qemu-img with qcow2 images of my VMs and
>  qemu-img finds them corrupted. I can reproduce the issue in the
>  following way (on -current, but is the same on -stable; tried different
>  hosts to exclude hardware errors):
>
>  marsden# vmctl create -s 300G test.qcow2
>  vmctl: qcow2 imagefile created
>  marsden# qemu-img check test.qcow2
>  No errors were found on the image.
>  Image end offset: 262144
>  marsden# vmctl start -cL -B net -b /bsd.rd -d test.qcow2 test
>
> <snipped out the install log>
>
>   marsden# qemu-img check test.qcow2
>  ERROR cluster 32769 refcount=0 reference=1
>
>  1 errors were found on the image.
>  Data may be corrupted, or further writes to the image may corrupt it.
>  39422/4915200 = 0.80% allocated, 3.31% fragmented, 0.00% compressed clusters
>  Image end offset: 2610888704
>
>  I've been able to reproduce the above, but interestingly if I "repair"
>  the qcow2 image using:
>
>  $ qemu-img -r all test.qcow2
>
>  It then reports 0 errors. Booting up the vm and installing packages like
>  python3 and git and then cloning some git repos to work the disk, it
>  still reports 0 errors.
>
>  Interestingly, if I install something like an Alpine 3.13 guest (just an
>  iso I had handy), qemu-img reports 0 errors.
>
>  I also looked at a handful of qcow2 images on one of my workstations and
>  seems only an Alpine and NixOS guest do not have this "corruption"
>  report. However, I've never experienced any noticeable abnormalities.
>
>  Since I see this from non-OpenBSD guests (Debian, for instance) it
>  doesn't seem to be our vioblk(4) driver and is probably vmd(8)'s qcow2
>  implementation..
>
>  Anyone familiar enough with qcow2 that might make heads or tails of
>  this? (cc'd ori@ as he was the original implementer.)
>
>  -dv
>
> Yeah, Ori would be the right person to answer. If not I can take a look if I
> find the time.


--
-Dave Voutila

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