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Re: [PATCH v2 2/6] block: truncate: Don't make backing file data visible
From: |
Alberto Garcia |
Subject: |
Re: [PATCH v2 2/6] block: truncate: Don't make backing file data visible |
Date: |
Fri, 22 Nov 2019 15:27:19 +0100 |
User-agent: |
Notmuch/0.18.2 (http://notmuchmail.org) Emacs/24.4.1 (i586-pc-linux-gnu) |
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 <address@hidden>
Reviewed-by: Alberto Garcia <address@hidden>
Berto
- [PATCH v2 2/6] block: truncate: Don't make backing file data visible, (continued)
- [PATCH v2 2/6] block: truncate: Don't make backing file data visible, Kevin Wolf, 2019/11/20
- Re: [PATCH v2 2/6] block: truncate: Don't make backing file data visible, Eric Blake, 2019/11/20
- Re: [PATCH v2 2/6] block: truncate: Don't make backing file data visible, Max Reitz, 2019/11/21
- Re: [PATCH v2 2/6] block: truncate: Don't make backing file data visible, Vladimir Sementsov-Ogievskiy, 2019/11/21
- Re: [PATCH v2 2/6] block: truncate: Don't make backing file data visible, Kevin Wolf, 2019/11/21
- Re: [PATCH v2 2/6] block: truncate: Don't make backing file data visible, Max Reitz, 2019/11/21
- Re: [PATCH v2 2/6] block: truncate: Don't make backing file data visible, Kevin Wolf, 2019/11/21
- Re: [PATCH v2 2/6] block: truncate: Don't make backing file data visible, Max Reitz, 2019/11/21
- Re: [PATCH v2 2/6] block: truncate: Don't make backing file data visible, Alberto Garcia, 2019/11/22
Re: [PATCH v2 2/6] block: truncate: Don't make backing file data visible,
Alberto Garcia <=
[PATCH v2 3/6] iotests: Add qemu_io_log(), Kevin Wolf, 2019/11/20
[PATCH v2 5/6] iotests: Support job-complete in run_job(), Kevin Wolf, 2019/11/20
[PATCH v2 4/6] iotests: Fix timeout in run_job(), Kevin Wolf, 2019/11/20
[PATCH v2 6/6] iotests: Test committing to short backing file, Kevin Wolf, 2019/11/20