Re: [patch]blk-mq: blk_mq_tag_to_rq should handle flush request

Ming Lei
2014-06-04T15:43:14Z

On Wed, Jun 4, 2014 at 11:31 PM, Christoph Hellwig <hch@infradead.org> wrote:
> On Wed, Jun 04, 2014 at 09:02:19AM -0600, Jens Axboe wrote:
>> >scsi_mq_find_tag only gets the scsi host, which may have multiple
>> >queues. When called from scsi_find_tag we actually have a scsi device,
>> >so that's not an issue, but when called from scsi_host_find_tag the
>> >driver only provides the host.
>>
>> Only solution I see right now is to have the flush_rq in the shared
>> tags, but that would potentially be a regression for multiple
>> devices and heavy flush uses cases. I'll see if I can come up with
>> something better, or maybe Shaohua has an idea.
>
> What about something like the following (untest, uncompiled, maybe
> pseudo-code):
>
> struct request *blk_mq_tag_to_rq(struct blk_mq_tags *tags, unsigned int tag)
> {
> struct request *rq = tags->rqs[tag];
>
> if ((rq->cmd_flags & REQ_FLUSH_SEQ) && rq->q->flush_rq->tag == tag)
> return rq->q->flush_rq;
> return rq;
> }

Looks we thought it together, :-)

Also maybe the flush_rq->tag need to be cleared in flush_end_io().

Thanks,
--
Ming Lei