From: Alberto Garcia <berto@igalia.com>
To: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org
Cc: kwolf@redhat.com, vsementsov@virtuozzo.com,
qemu-devel@nongnu.org, stefanha@redhat.com, mreitz@redhat.com
Subject: Re: [PATCH v2 2/6] block: truncate: Don't make backing file data visible
Date: Fri, 22 Nov 2019 15:27:19 +0100 [thread overview]
Message-ID: <w51eey00ywo.fsf@maestria.local.igalia.com> (raw)
In-Reply-To: <20191120184501.28159-3-kwolf@redhat.com>
On Wed 20 Nov 2019 07:44:57 PM CET, Kevin Wolf wrote:
> When extending the size of an image that has a backing file larger than
> its old size, make sure that the backing file data doesn't become
> visible in the guest, but the added area is properly zeroed out.
>
> Consider the following scenario where the overlay is shorter than its
> backing file:
>
> base.qcow2: AAAAAAAA
> overlay.qcow2: BBBB
>
> When resizing (extending) overlay.qcow2, the new blocks should not stay
> unallocated and make the additional As from base.qcow2 visible like
> before this patch, but zeros should be read.
>
> A similar case happens with the various variants of a commit job when an
> intermediate file is short (- for unallocated):
>
> base.qcow2: A-A-AAAA
> mid.qcow2: BB-B
> top.qcow2: C--C--C-
>
> After commit top.qcow2 to mid.qcow2, the following happens:
>
> mid.qcow2: CB-C00C0 (correct result)
> mid.qcow2: CB-C--C- (before this fix)
>
> Without the fix, blocks that previously read as zeros on top.qcow2
> suddenly turn into A.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Berto
next prev parent reply other threads:[~2019-11-22 14:28 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-20 18:44 [PATCH for-4.2? v2 0/6] block: Fix resize (extending) of short overlays Kevin Wolf
2019-11-20 18:44 ` [PATCH v2 1/6] block: bdrv_co_do_pwrite_zeroes: 64 bit 'bytes' parameter Kevin Wolf
2019-11-20 18:44 ` [PATCH v2 2/6] block: truncate: Don't make backing file data visible Kevin Wolf
2019-11-20 21:15 ` Eric Blake
2019-11-21 11:22 ` Kevin Wolf
2019-11-21 8:59 ` Max Reitz
2019-11-21 9:46 ` Vladimir Sementsov-Ogievskiy
2019-11-21 11:34 ` Kevin Wolf
2019-11-21 12:21 ` Max Reitz
2019-11-21 14:33 ` Kevin Wolf
2019-11-21 15:25 ` Max Reitz
2019-11-22 14:07 ` Alberto Garcia
2019-11-22 14:27 ` Alberto Garcia [this message]
2019-11-20 18:44 ` [PATCH v2 3/6] iotests: Add qemu_io_log() Kevin Wolf
2019-11-21 13:35 ` Alberto Garcia
2019-11-20 18:44 ` [PATCH v2 4/6] iotests: Fix timeout in run_job() Kevin Wolf
2019-11-21 13:34 ` Alberto Garcia
2019-11-20 18:45 ` [PATCH v2 5/6] iotests: Support job-complete " Kevin Wolf
2019-11-21 13:35 ` Alberto Garcia
2019-11-20 18:45 ` [PATCH v2 6/6] iotests: Test committing to short backing file Kevin Wolf
2019-11-20 21:27 ` Eric Blake
2019-11-21 9:36 ` Vladimir Sementsov-Ogievskiy
2019-11-21 10:24 ` Vladimir Sementsov-Ogievskiy
2019-11-21 10:28 ` Vladimir Sementsov-Ogievskiy
2019-11-21 10:30 ` Vladimir Sementsov-Ogievskiy
2019-11-21 11:39 ` Kevin Wolf
2019-11-21 13:02 ` Vladimir Sementsov-Ogievskiy
2019-11-21 14:09 ` [PATCH for-4.2? v2 0/6] block: Fix resize (extending) of short overlays Stefan Hajnoczi
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