request queue

Linux 6.18.37 LTS: block/blk-mq.c
Linux 6.18.37 LTS: block/blk-core.c
Linux 6.18.37 LTS: include/linux/blk-mq.h

		bio->bi_ioprio = get_current_ioprio();
	blkcg_set_ioprio(bio);
}

/**
 * blk_mq_submit_bio - Create and send a request to block device.
 * @bio: Bio pointer.
 *
 * Builds up a request structure from @q and @bio and send to the device. The
 * request may not be queued directly to hardware if:
 * * This request can be merged with another one
 * * We want to place request at plug queue for possible future merging
 * * There is an IO scheduler active at this queue
 *
 * It will not queue the request if there is an error with the bio, or at the
 * request creation.
 */
void blk_mq_submit_bio(struct bio *bio)
{
	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
	struct blk_plug *plug = blk_mq_plug(bio);
	const int is_sync = op_is_sync(bio->bi_opf);
	struct blk_mq_hw_ctx *hctx;
	struct request *rq;
	unsigned int nr_segs = 1;
	blk_status_t ret;

	bio = blk_queue_bounce(bio, q);
	if (bio_may_exceed_limits(bio, &q->limits)) {
		bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);
		if (!bio)
			return;
	}

	if (!bio_integrity_prep(bio))
		return;

	bio_set_ioprio(bio);

	rq = blk_mq_get_cached_request(q, plug, &bio, nr_segs);

	mutex_lock(&q->mq_freeze_lock);
	if (++q->mq_freeze_depth == 1) {
		percpu_ref_kill(&q->q_usage_counter);
		mutex_unlock(&q->mq_freeze_lock);
		if (queue_is_mq(q))
			blk_mq_run_hw_queues(q, false);
	} else {
		mutex_unlock(&q->mq_freeze_lock);
	}
}
EXPORT_SYMBOL_GPL(blk_freeze_queue_start);

void blk_mq_freeze_queue_wait(struct request_queue *q)
{
	wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->q_usage_counter));
}
EXPORT_SYMBOL_GPL(blk_mq_freeze_queue_wait);

int blk_mq_freeze_queue_wait_timeout(struct request_queue *q,
				     unsigned long timeout)
{
	return wait_event_timeout(q->mq_freeze_wq,
					percpu_ref_is_zero(&q->q_usage_counter),
					timeout);
}
EXPORT_SYMBOL_GPL(blk_mq_freeze_queue_wait_timeout);

/*
 * Guarantee no request is in use, so we can change any data structure of
 * the queue afterward.
 */
void blk_freeze_queue(struct request_queue *q)
{
	/*
	 * In the !blk_mq case we are only calling this to kill the
	 * q_usage_counter, otherwise this increases the freeze depth
	 * and waits for it to return to zero.  For this reason there is
	 * no blk_unfreeze_queue(), and blk_freeze_queue() is not
	 * exported to drivers as the only user for unfreeze is blk_mq.
	 */