Re: [Qemu-devel] [PATCH v2 1/2] block: fix overlapping multiwrite requests

[Eric Blake <eblake@redhat.com>]

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On 07/30/2014 02:53 AM, 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 <sviatoslav.pestov@gmail.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  block.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 

Reviewed-by: Eric Blake <eblake@redhat.com>

Technically a bug fix, so okay for 2.1 if desired; but it is awfully
late and as you said it is fairly unlikely for guests to be relying on
overlapping multiwrite, so I'm okay with the decision to delay it to 2.2
and just have stable 2.1.1/downstream backports.

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


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