On 11/23/2016 04:39 AM, Olaf Hering wrote:
> The guest sends discard requests as u64 sector/count pairs, but the
> block layer operates internally with s64/s32 pairs. The conversion
> leads to IO errors in the guest, the discard request is not processed.
> 
>   domU.cfg:
>   'vdev=xvda, format=qcow2, backendtype=qdisk, target=/x.qcow2'
>   domU:
>   mkfs.ext4 -F /dev/xvda
>   Discarding device blocks: failed - Input/output error
> 
> Fix this by splitting the request into chunks of BDRV_REQUEST_MAX_SECTORS.
> Add input range checking to avoid overflow.
> 
> Fixes f313520 ("xen_disk: add discard support")
> 
> Signed-off-by: Olaf Hering <olaf@aepfle.de>
> ---

Qualifies as a bug fix, so requesting 2.8 inclusion.
Reviewed-by: Eric Blake <eblake@redhat.com>

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