linux-kernel - Re: [patch]blk-mq: blk_mq_tag_to

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Date:	Wed, 4 Jun 2014 23:43:11 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jens Axboe <axboe@...nel.dk>, Shaohua Li <shli@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch]blk-mq: blk_mq_tag_to_rq should handle flush request

On Wed, Jun 4, 2014 at 11:31 PM, Christoph Hellwig <hch@...radead.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
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