From: "Denis V. Lunev" <den@virtuozzo.com>
To: Konstantin Khorenko <khorenko@virtuozzo.com>,
Alexander Ivanov <alexander.ivanov@virtuozzo.com>
Cc: devel@openvz.org
Subject: Re: [Devel] [PATCH hci-8.1] drivers/md/dm-qcow2: truncate unused tail of image on suspend
Date: Tue, 6 Oct 2026 17:56:37 +0200 [thread overview]
Message-ID: <e1227b97-e11c-44b7-ae64-23f27eb6d5f5@virtuozzo.com> (raw)
In-Reply-To: <179130196660.914346.14420180134509591837.b4-review@b4>
On 10/6/26 17:52, Konstantin Khorenko wrote:
>> drivers/md/dm-qcow2: truncate unused tail of image on suspend
> ...
>> Truncate the file to min(file_preallocated_area_start, used end).
>> Skip the scan if md writeback failed, as refcounts on disk are stale
>> then, and fall back to the old behaviour on scan error.
> There is one more case of stale refcounts on disk: an image with
> INCOMPATIBLE_FEATURES_DIRTY_BIT set. qcow2_check_convert_hdr() accepts it
> (the check is commented out), and with qemu lazy refcounts that bit means
> refcounts were not written for the last allocations, so they are too low.
>
> Today such an image loses data only when the allocator hands out a
> cluster whose refcount is zero but which L2 still references. After this
> patch the first suspend truncates live clusters at the tail without a
> single write to the device. The image is already invalid per spec, so
> this is not a regression in the strict sense, but either the commit
> message should say that a dirty image is not supported, or the dirty-bit
> check in qcow2_check_convert_hdr() should come back.
Image should go clean into the kernel on first pass.
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next prev parent reply other threads:[~2026-10-06 15:58 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-06 14:44 Alexander Ivanov
2026-10-06 14:45 ` Denis V. Lunev
2026-10-06 14:49 ` no-reply
2026-10-06 15:52 ` Konstantin Khorenko
2026-10-06 15:56 ` Denis V. Lunev [this message]
2026-10-06 17:39 ` Konstantin Khorenko
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