block: introduce a function submit_bio_noacct_mq_direct

Introduce a function that submits bio to a request-based device driver.
The function doesn't offload requests to current->bio_list. It is expected
to be called from device mapper, where current->bio_list is already set
up.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 block/blk-core.c       |   16 ++++++++++++++++
 include/linux/blkdev.h |    1 +
 2 files changed, 17 insertions(+)

Index: linux-2.6/block/blk-core.c
===================================================================
--- linux-2.6.orig/block/blk-core.c	2021-03-01 19:47:27.000000000 +0100
+++ linux-2.6/block/blk-core.c	2021-03-02 10:43:28.000000000 +0100
@@ -992,6 +992,22 @@ static blk_qc_t __submit_bio_noacct(stru
 	return ret;
 }
 
+blk_qc_t submit_bio_noacct_mq_direct(struct bio *bio)
+{
+	struct gendisk *disk = bio->bi_bdev->bd_disk;
+
+	if (unlikely(bio_queue_enter(bio) != 0))
+		return BLK_QC_T_NONE;
+	
+	if (!blk_crypto_bio_prep(&bio)) {
+		blk_queue_exit(disk->queue);
+		return BLK_QC_T_NONE;
+	}
+
+	return blk_mq_submit_bio(bio);
+}
+EXPORT_SYMBOL(submit_bio_noacct_mq_direct);
+
 static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
 {
 	struct bio_list bio_list[2] = { };
Index: linux-2.6/include/linux/blkdev.h
===================================================================
--- linux-2.6.orig/include/linux/blkdev.h	2021-03-01 19:47:29.000000000 +0100
+++ linux-2.6/include/linux/blkdev.h	2021-03-02 10:44:04.000000000 +0100
@@ -912,6 +912,7 @@ static inline void rq_flush_dcache_pages
 
 extern int blk_register_queue(struct gendisk *disk);
 extern void blk_unregister_queue(struct gendisk *disk);
+blk_qc_t submit_bio_noacct_mq_direct(struct bio *bio);
 blk_qc_t submit_bio_noacct(struct bio *bio);
 extern void blk_rq_init(struct request_queue *q, struct request *rq);
 extern void blk_put_request(struct request *);