Re: [PATCH for-5.1 v2 1/2] block/block-copy: always align copied region to cluster size

From: Max Reitz <mreitz@redhat.com>
To: Stefan Reiter <s.reiter@proxmox.com>, qemu-block@nongnu.org
Cc: kwolf@redhat.com, vsementsov@virtuozzo.com, qemu-devel@nongnu.org
Subject: Re: [PATCH for-5.1 v2 1/2] block/block-copy: always align copied region to cluster size
Date: Mon, 10 Aug 2020 17:15:26 +0200	[thread overview]
Message-ID: <8fd06678-0f68-0cfc-b15a-c793f8f231cd@redhat.com> (raw)
In-Reply-To: <20200810095523.15071-1-s.reiter@proxmox.com>

[-- Attachment #1.1: Type: text/plain, Size: 1463 bytes --]

On 10.08.20 11:55, Stefan Reiter wrote:
> Since commit 42ac214406e0 (block/block-copy: refactor task creation)
> block_copy_task_create calculates the area to be copied via
> bdrv_dirty_bitmap_next_dirty_area, but that can return an unaligned byte
> count if the image's last cluster end is not aligned to the bitmap's
> granularity.
> 
> Always ALIGN_UP the resulting bytes value to satisfy block_copy_do_copy,
> which requires the 'bytes' parameter to be aligned to cluster size.
> 
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
> ---
> 
> I've now marked it for-5.1 since it is just a fix, but it's probably okay if
> done later as well.

42ac214406e0 wasn’t in 5.0, so this would be a regression if we don’t
get it in 5.1.  I suppose this is an edge case, because most images
should be aligned to the cluster size, but I think objectively this is
something for 5.1.

So I’ll apply this series to my block branch:

https://git.xanclic.moe/XanClic/qemu/commits/branch/block

And I think I’m going to send a pull request tomorrow morning.  I see
there’s another patch for 5.1 on the list, so it should be OK.

If you want me to act on any of the suggestions I gave on your test,
feel free to say so and I’ll handle those that make sense to you (like,
I hope the s/4097/4096/ thing perhaps).

Thanks for finding and fixing this!

Max

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 488 bytes --]