[PATCH 1/4] block: introduce submit_bio_noacct_add_head

[dannyshih <dannyshih@synology.com>]

From: Danny Shih <dannyshih@synology.com>

Porvide a way for stacking block device to re-submit the bio
which sholud be handled firstly.

Signed-off-by: Danny Shih <dannyshih@synology.com>
Reviewed-by: Allen Peng <allenpeng@synology.com>
Reviewed-by: Alex Wu <alexwu@synology.com>
---
 block/blk-core.c       | 44 +++++++++++++++++++++++++++++++++-----------
 include/linux/blkdev.h |  1 +
 2 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 96e5fcd..693dc83 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1031,16 +1031,7 @@ static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
 	return ret;
 }
 
-/**
- * submit_bio_noacct - re-submit a bio to the block device layer for I/O
- * @bio:  The bio describing the location in memory and on the device.
- *
- * This is a version of submit_bio() that shall only be used for I/O that is
- * resubmitted to lower level drivers by stacking block drivers.  All file
- * systems and other upper level users of the block layer should use
- * submit_bio() instead.
- */
-blk_qc_t submit_bio_noacct(struct bio *bio)
+static blk_qc_t do_submit_bio_noacct(struct bio *bio, bool add_head)
 {
 	if (!submit_bio_checks(bio))
 		return BLK_QC_T_NONE;
@@ -1052,7 +1043,10 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
 	 * it is active, and then process them after it returned.
 	 */
 	if (current->bio_list) {
-		bio_list_add(&current->bio_list[0], bio);
+		if (add_head)
+			bio_list_add_head(&current->bio_list[0], bio);
+		else
+			bio_list_add(&current->bio_list[0], bio);
 		return BLK_QC_T_NONE;
 	}
 
@@ -1060,9 +1054,37 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
 		return __submit_bio_noacct_mq(bio);
 	return __submit_bio_noacct(bio);
 }
+
+/**
+ * submit_bio_noacct - re-submit a bio to the block device layer for I/O
+ * @bio:  The bio describing the location in memory and on the device.
+ *
+ * This is a version of submit_bio() that shall only be used for I/O that is
+ * resubmitted to lower level drivers by stacking block drivers.  All file
+ * systems and other upper level users of the block layer should use
+ * submit_bio() instead.
+ */
+blk_qc_t submit_bio_noacct(struct bio *bio)
+{
+	return do_submit_bio_noacct(bio, false);
+}
 EXPORT_SYMBOL(submit_bio_noacct);
 
 /**
+ * submit_bio_noacct - re-submit a bio, which needs to be handle firstly,
+ *                     to the block device layer for I/O
+ * @bio:  The bio describing the location in memory and on the device.
+ *
+ * alternative submit_bio_noacct() which add bio to the head of
+ * current->bio_list.
+ */
+blk_qc_t submit_bio_noacct_add_head(struct bio *bio)
+{
+	return do_submit_bio_noacct(bio, true);
+}
+EXPORT_SYMBOL(submit_bio_noacct_add_head);
+
+/**
  * submit_bio - submit a bio to the block device layer for I/O
  * @bio: The &struct bio which describes the I/O
  *
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 070de09..b0080d0 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -905,6 +905,7 @@ static inline void rq_flush_dcache_pages(struct request *rq)
 extern int blk_register_queue(struct gendisk *disk);
 extern void blk_unregister_queue(struct gendisk *disk);
 blk_qc_t submit_bio_noacct(struct bio *bio);
+blk_qc_t submit_bio_noacct_add_head(struct bio *bio);
 extern void blk_rq_init(struct request_queue *q, struct request *rq);
 extern void blk_put_request(struct request *);
 extern struct request *blk_get_request(struct request_queue *, unsigned int op,
-- 
2.7.4