blk-mq: Add a flag for reserved requests

Add a flag for reserved requests so that drivers may know this for any
special handling.
Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/1657109034-206040-3-git-send-email-john.garry@huawei.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -475,6 +475,9 @@ static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data)
 	if (!(data->rq_flags & RQF_ELV))
 		blk_mq_tag_busy(data->hctx);
 
+	if (data->flags & BLK_MQ_REQ_RESERVED)
+		data->rq_flags |= RQF_RESV;
+
 	/*
 	 * Try batched alloc if we want more than 1 tag.
 	 */
@@ -589,6 +592,9 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
 	else
 		data.rq_flags |= RQF_ELV;
 
+	if (flags & BLK_MQ_REQ_RESERVED)
+		data.rq_flags |= RQF_RESV;
+
 	ret = -EWOULDBLOCK;
 	tag = blk_mq_get_tag(&data);
 	if (tag == BLK_MQ_NO_TAG)

include/linux/blk-mq.h

@@ -57,6 +57,7 @@ typedef __u32 __bitwise req_flags_t;
 #define RQF_TIMED_OUT		((__force req_flags_t)(1 << 21))
 /* queue has elevator attached */
 #define RQF_ELV			((__force req_flags_t)(1 << 22))
+#define RQF_RESV			((__force req_flags_t)(1 << 23))
 
 /* flags that prevent us from merging requests: */
 #define RQF_NOMERGE_FLAGS \
@@ -825,6 +826,11 @@ static inline bool blk_mq_need_time_stamp(struct request *rq)
 	return (rq->rq_flags & (RQF_IO_STAT | RQF_STATS | RQF_ELV));
 }
 
+static inline bool blk_mq_is_reserved_rq(struct request *rq)
+{
+	return rq->rq_flags & RQF_RESV;
+}
+
 /*
  * Batched completions only work when there is no I/O error and no special
  * ->end_io handler.