From: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
To: "Denis V. Lunev" <den@openvz.org>
Cc: svt-core@virtuozzo.com
Subject: Re: [PATCH hci-8.1 1/1] qcow2: fix subcluster discard punching data shared with a snapshot #VSTOR-144873
Date: Tue, 27 Oct 2026 11:21:00 +0200 [thread overview]
Message-ID: <88b4a044-f5e9-4e39-ad2e-89cf0dd4480d@virtuozzo.com> (raw)
In-Reply-To: <20261026193715.828224-2-den@openvz.org>
On 10/26/26 9:37 PM, Denis V. Lunev wrote:
> From: Denis V. Lunev <den@openvz.org>
>
> discard_l2_subclusters() passes the discarded range down to the host
> file even when the cluster is still referenced by an internal snapshot.
> 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.
>
> Pass the discard down only for a cluster with QCOW_OFLAG_COPIED set,
> i.e. one owned by the active layer alone. A shared cluster gets only
> its active L2 bitmap updated, as a whole-cluster discard already does
> by dropping the refcount instead of punching the host file.
>
> Cover it in iotest 271.
>
> Fixes: 225b4de1249 ("qcow2: make subclusters discardable")
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> ---
> [...]
Reviewed-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
prev parent reply other threads:[~2026-10-27 9:21 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-26 19:37 [PATCH hci-8.1 0/1] qcow2: fix guest TRIM destroying internal snapshot data #VSTOR-144873 Denis V. Lunev
2026-10-26 19:37 ` [PATCH hci-8.1 1/1] qcow2: fix subcluster discard punching data shared with a snapshot #VSTOR-144873 Denis V. Lunev
2026-10-27 9:21 ` Andrey Drobyshev [this message]
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