From: no-reply@sashiko.virtuozzo.com
To: svt-core@virtuozzo.com,
Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
Cc: den@openvz.org, andrey.drobyshev@virtuozzo.com
Subject: Re: [PATCH hci-8.1 1/2] qcow2: fix snapshot data corruption with discard-no-unref=on #VSTOR-151885
Date: Tue, 27 Oct 2026 10:28:48 +0000 [thread overview]
Message-ID: <010701a17ce7ce68-aae9b75b-ab89-4c27-b2d3-675ab581ce57-000000@eu-central-1.amazonses.com> (raw)
In-Reply-To: <20261027102618.798471-2-andrey.drobyshev@virtuozzo.com>
> Whenever option discard-no-unref=on is enabled, we bypass refcount
> machinery and unconditionally punch hole in the data on 'discard' and
> 'write -z -u' paths. However, when this same cluster is also referenced
> by an internal snapshot, such operations lead to problems. The active L2
> table is copied before it is changed, so the snapshot metadata stays
> correct, but the host range under it is punched out and the snapshot reads
> zeroes there afterwards. qemu-img check finds nothing wrong.
>
> Fix this by guarding the 'keep_reference' flag by the presence of the
> QCOW_OFLAG_COPIED bit. I.e. only proceed with unconditional data
> punching if we own this cluster exclusively.
>
> Fixes: 42a2890a76f4 ("qcow2: add discard-no-unref option")
> Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
Sashiko has reviewed this patch and found no issues. It looks great!
--
Sashiko AI review · https://sashiko.vzint.dev/#/patchset/20261027102618.798471-1-andrey.drobyshev@virtuozzo.com?part=1
next prev parent reply other threads:[~2026-10-27 10:28 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-27 10:26 [PATCH hci-8.1 0/2] qcow2: fix discard-no-unref=on data corruption #VSTOR-151885 Andrey Drobyshev
2026-10-27 10:26 ` [PATCH hci-8.1 1/2] qcow2: fix snapshot data corruption with discard-no-unref=on #VSTOR-151885 Andrey Drobyshev
2026-10-27 10:28 ` no-reply [this message]
2026-10-27 10:26 ` [PATCH hci-8.1 2/2] iotests/290: add 'discard' and 'write -z -u' case with a snapshot #VSTOR-151885 Andrey Drobyshev
2026-10-27 10:28 ` no-reply
2026-10-27 11:04 ` [PATCH hci-8.1 0/2] qcow2: fix discard-no-unref=on data corruption #VSTOR-151885 Denis V. Lunev
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