On 04/19/2017 01:45 AM, Christoph Hellwig wrote:
>
>> + if (bio->bi_opf & REQ_NOWAIT) {
>> + if (!blk_queue_nowait(q)) {
>> + err = -EOPNOTSUPP;
>> + goto end_io;
>> + }
>> + if (!(bio->bi_opf & REQ_SYNC)) {
>
> I don't understand this check at all..
It is to ensure at the block layer that NOWAIT comes only for DIRECT
calls only. I should probably change it to REQ_SYNC | REQ_IDLE.
>
>> + if (unlikely(!blk_queue_dying(q) && (bio->bi_opf &
>> REQ_NOWAIT)))
>
> Please break lines after 80 characters.
>
>> @@ -119,6 +119,9 @@ struct request *blk_mq_sched_get_request(struct
>> request_queue *q,
>> if (likely(!data->hctx))
>> data->hctx = blk_mq_map_queue(q, data->ctx->cpu);
>>
>> + if (bio && (bio->bi_opf & REQ_NOWAIT))
>> + data->flags |= BLK_MQ_REQ_NOWAIT;
>
> Check the op flag again here.
>
>> +++ b/block/blk-mq.c
>> @@ -1538,6 +1538,8 @@ static blk_qc_t blk_mq_make_request(struct
>> request_queue *q, struct bio *bio)
>> rq = blk_mq_sched_get_request(q, bio, bio->bi_opf, &data);
>> if (unlikely(!rq)) {
>> __wbt_done(q->rq_wb, wb_acct);
>> + if (bio && (bio->bi_opf & REQ_NOWAIT))
>> + bio_wouldblock_error(bio);
>
> bio iѕ dereferences unconditionally above, so you can do the same.
>
>> @@ -1662,6 +1664,8 @@ static blk_qc_t blk_sq_make_request(struct
>> request_queue *q, struct bio *bio)
>> rq = blk_mq_sched_get_request(q, bio, bio->bi_opf, &data);
>> if (unlikely(!rq)) {
>> __wbt_done(q->rq_wb, wb_acct);
>> + if (bio && (bio->bi_opf & REQ_NOWAIT))
>> + bio_wouldblock_error(bio);
>
> Same here. Although blk_sq_make_request is gone anyway in the current
> block tree..
>
>> + /* Request queue supports BIO_NOWAIT */
>> + queue_flag_set_unlocked(QUEUE_FLAG_NOWAIT, q);
>
> BIO_NOWAIT is gone. And the comment would not be needed if the
> flag had a more descriptive name, e.g. QUEUE_FLAG_NOWAIT_SUPPORT.
>
> And I think all request based drivers should set the flag implicitly
> as ->queuecommand can't sleep, and ->queue_rq only when it's always
> offloaded to a workqueue when the BLK_MQ_F_BLOCKING flag is set.
>
Yes, Do we have a central point (like a probe() function call?) where
this can be done?
--
Goldwyn
