[Xen-devel] Re: [PATCH 2/3] xen/blkback: Fix the inhibition to map pages when discarding sector ranges.

[Li Dongyang <lidongyang@xxxxxxxxxx>]

On Tue, Oct 11, 2011 at 3:25 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>> On 10.10.11 at 17:28, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 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@xxxxxxxxxx>
>> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
>> ---
>>  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).
>
Ah, you are right, we could remove this check then, Thanks
> Jan
>
>>                       xen_blkbk_map(req, pending_req, seg))
>>               goto fail_flush;
>>
>
>
>
>

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