qemu-devel
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH v7 07/10] block: truncate: Don't make backing file data visib


From: Max Reitz
Subject: Re: [PATCH v7 07/10] block: truncate: Don't make backing file data visible
Date: Fri, 24 Apr 2020 16:09:41 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0

On 24.04.20 14:54, 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: Vladimir Sementsov-Ogievskiy <address@hidden>
> ---
>  block/io.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)

Reviewed-by: Max Reitz <address@hidden>

Attachment: signature.asc
Description: OpenPGP digital signature


reply via email to

[Prev in Thread] Current Thread [Next in Thread]