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Re: [Qemu-devel] [PATCH v2 1/2] block: fix overlapping multiwrite reques
From: |
Benoît Canet |
Subject: |
Re: [Qemu-devel] [PATCH v2 1/2] block: fix overlapping multiwrite requests |
Date: |
Thu, 31 Jul 2014 09:41:57 +0200 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
The Wednesday 30 Jul 2014 à 09:53:30 (+0100), Stefan Hajnoczi wrote :
> When request A is a strict superset of request B:
>
> AAAAAAAA
> BBBB
>
> multiwrite_merge() merges them as follows:
>
> AABBBB
>
> The tail of request A should have been included:
>
> AABBBBAA
>
> This patch fixes data loss but this code path is probably rare. Since
> guests cannot assume ordering between in-flight requests, few
> applications submit overlapping write requests.
>
> Reported-by: Slava Pestov <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
> block.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/block.c b/block.c
> index 8cf519b..0a3ac43 100644
> --- a/block.c
> +++ b/block.c
> @@ -4498,6 +4498,12 @@ static int multiwrite_merge(BlockDriverState *bs,
> BlockRequest *reqs,
> // Add the second request
> qemu_iovec_concat(qiov, reqs[i].qiov, 0, reqs[i].qiov->size);
>
> + // Add tail of first request, if necessary
> + if (qiov->size < reqs[outidx].qiov->size) {
> + qemu_iovec_concat(qiov, reqs[outidx].qiov, qiov->size,
> + reqs[outidx].qiov->size - qiov->size);
> + }
> +
> reqs[outidx].nb_sectors = qiov->size >> 9;
> reqs[outidx].qiov = qiov;
>
> --
> 1.9.3
>
>
Seems to make sense.
Reviewed-by: Benoit Canet <address@hidden>