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SubjectRe: [PATCH 2/3] xen/blkback: Fix the inhibition to map pages when discarding sector ranges.
>>> On 10.10.11 at 17:28, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
> The 'operation' parameters are the ones provided to the bio layer while
> the req->operation are the ones passed in between the backend and
> frontend. We used the wrong 'operation' value to squash the
> call to map pages when processing the discard operation resulting
> in mapping the pages unnecessarily.
>
> CC: Li Dongyang <lidongyang@novell.com>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> ---
> drivers/block/xen-blkback/blkback.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/block/xen-blkback/blkback.c
> b/drivers/block/xen-blkback/blkback.c
> index 184b133..3da9a40 100644
> --- a/drivers/block/xen-blkback/blkback.c
> +++ b/drivers/block/xen-blkback/blkback.c
> @@ -707,7 +707,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
> * the hypercall to unmap the grants - that is all done in
> * xen_blkbk_unmap.
> */
> - if (operation != BLKIF_OP_DISCARD &&
> + if (operation != REQ_DISCARD &&

Why is that check necessary in the first place? xen_blkbk_map() doesn't
do any harm when req->nr_segments is zero (as could also be the case
on WRITE_FLUSH ones).

Jan

> xen_blkbk_map(req, pending_req, seg))
> goto fail_flush;
>






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