Re: [Qemu-devel] [PATCH 3/6] qcow2: simplify logic in qcow2_co_write_zeroes

From: Eric Blake <eblake@redhat.com>
To: "Denis V. Lunev" <den@openvz.org>, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 3/6] qcow2: simplify logic in qcow2_co_write_zeroes
Date: Mon, 16 May 2016 10:28:18 -0600	[thread overview]
Message-ID: <5739F522.1080505@redhat.com> (raw)
In-Reply-To: <1463227273-27523-4-git-send-email-den@openvz.org>

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On 05/14/2016 06:01 AM, Denis V. Lunev wrote:
> Unaligned request could occupy only one cluster. This is true since the

s/request could/requests will/

> previous commit. Simplify the code taking this considiration into

s/considiration/consideration/

> account.
> 
> There are no other changes so far.
> 
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/qcow2.c | 23 +++++------------------
>  1 file changed, 5 insertions(+), 18 deletions(-)
> 
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 62febfc..9a54bbd 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -2436,33 +2436,20 @@ static coroutine_fn int qcow2_co_write_zeroes(BlockDriverState *bs,
>      int tail = (sector_num + nb_sectors) % s->cluster_sectors;
>  
>      if (head != 0 || tail != 0) {
> -        int64_t cl_end = -1;
> +        int64_t cl_start = sector_num - head;
>  
> -        sector_num -= head;
> -        nb_sectors += head;
> +        assert(cl_start + s->cluster_sectors >= sector_num + nb_sectors);

In other words, the caller is now buggy if it ever passes us an
unaligned request that crosses cluster boundaries (the only requests
that can cross boundaries will be aligned).

With the grammar fix in the commit message,
Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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