[RFC PATCH v2 2/9] block: add rd_hint to bio and request

[Bob Liu <bob.liu@oracle.com>]

rd_hint is a bitmap for stacked layer support(see patch 4/9),
set a bit to 1 means already read from the corresponding mirror device.

rd_hint will be set properly recording read i/o went to which real device
during end_bio().
If the upper layer want to retry other mirrors, just preserve the returned
bi_rd_hint and resubmit bio.

The upper layer e.g fs can set bitmap_zero(rd_hint) if don't care about alt
mirror device retry feature which is also the default setting.

Signed-off-by: Bob Liu <bob.liu@oracle.com>
---
 Documentation/block/biodoc.txt | 3 +++
 block/bio.c                    | 1 +
 block/blk-core.c               | 1 +
 block/blk-merge.c              | 6 ++++++
 block/bounce.c                 | 1 +
 drivers/md/raid1.c             | 1 +
 include/linux/blk_types.h      | 1 +
 include/linux/blkdev.h         | 1 +
 8 files changed, 15 insertions(+)

diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt
index ac18b488cb5e..c6b5dfc9314b 100644
--- a/Documentation/block/biodoc.txt
+++ b/Documentation/block/biodoc.txt
@@ -430,6 +430,7 @@ struct bio {
        struct bio          *bi_next;    /* request queue link */
        struct block_device *bi_bdev;	/* target device */
        unsigned long       bi_flags;    /* status, command, etc */
+       DECLARE_BITMAP(bi_rd_hint, BLKDEV_MAX_MIRRORS); /* bio read hint */
        unsigned long       bi_opf;       /* low bits: r/w, high: priority */
 
        unsigned int	bi_vcnt;     /* how may bio_vec's */
@@ -464,6 +465,8 @@ With this multipage bio design:
   (e.g a 1MB bio_vec needs to be handled in max 128kB chunks for IDE)
   [TBD: Should preferably also have a bi_voffset and bi_vlen to avoid modifying
    bi_offset an len fields]
+- bi_rd_hint is an in/out bitmap parameter, set a bit to 1 means already read
+  from the corresponding mirror device.
 
 (*) unrelated merges -- a request ends up containing two or more bios that
     didn't originate from the same place.
diff --git a/block/bio.c b/block/bio.c
index 4db1008309ed..0e97d75edbd4 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -606,6 +606,7 @@ void __bio_clone_fast(struct bio *bio, struct bio *bio_src)
 	bio->bi_opf = bio_src->bi_opf;
 	bio->bi_ioprio = bio_src->bi_ioprio;
 	bio->bi_write_hint = bio_src->bi_write_hint;
+	bitmap_copy(bio->bi_rd_hint, bio_src->bi_rd_hint, BLKDEV_MAX_MIRRORS);
 	bio->bi_iter = bio_src->bi_iter;
 	bio->bi_io_vec = bio_src->bi_io_vec;
 
diff --git a/block/blk-core.c b/block/blk-core.c
index b838c6dc5357..c93162b7140c 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -742,6 +742,7 @@ void blk_init_request_from_bio(struct request *req, struct bio *bio)
 	req->__sector = bio->bi_iter.bi_sector;
 	req->ioprio = bio_prio(bio);
 	req->write_hint = bio->bi_write_hint;
+	bitmap_copy(req->rd_hint, bio->bi_rd_hint, BLKDEV_MAX_MIRRORS);
 	blk_rq_bio_prep(req->q, req, bio);
 }
 EXPORT_SYMBOL_GPL(blk_init_request_from_bio);
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 71e9ac03f621..58982a80eca8 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -745,6 +745,9 @@ static struct request *attempt_merge(struct request_queue *q,
 	if (req->write_hint != next->write_hint)
 		return NULL;
 
+	if (!bitmap_equal(req->rd_hint, next->rd_hint, BLKDEV_MAX_MIRRORS))
+		return NULL;
+
 	if (req->ioprio != next->ioprio)
 		return NULL;
 
@@ -877,6 +880,9 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 	if (rq->write_hint != bio->bi_write_hint)
 		return false;
 
+	if (!bitmap_equal(rq->rd_hint, bio->bi_rd_hint, BLKDEV_MAX_MIRRORS))
+		return false;
+
 	if (rq->ioprio != bio_prio(bio))
 		return false;
 
diff --git a/block/bounce.c b/block/bounce.c
index ffb9e9ecfa7e..fba66e06b735 100644
--- a/block/bounce.c
+++ b/block/bounce.c
@@ -250,6 +250,7 @@ static struct bio *bounce_clone_bio(struct bio *bio_src, gfp_t gfp_mask,
 	bio->bi_opf		= bio_src->bi_opf;
 	bio->bi_ioprio		= bio_src->bi_ioprio;
 	bio->bi_write_hint	= bio_src->bi_write_hint;
+	bitmap_copy(bio->bi_rd_hint, bio_src->bi_rd_hint, BLKDEV_MAX_MIRRORS);
 	bio->bi_iter.bi_sector	= bio_src->bi_iter.bi_sector;
 	bio->bi_iter.bi_size	= bio_src->bi_iter.bi_size;
 
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 1d54109071cc..1e5a51f22332 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1103,6 +1103,7 @@ static void alloc_behind_master_bio(struct r1bio *r1_bio,
 	}
 
 	behind_bio->bi_write_hint = bio->bi_write_hint;
+	bitmap_copy(behind_bio->bi_rd_hint, bio->bi_rd_hint, BLKDEV_MAX_MIRRORS);
 
 	while (i < vcnt && size) {
 		struct page *page;
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index d66bf5f32610..49bdd96e2623 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -151,6 +151,7 @@ struct bio {
 	unsigned short		bi_flags;	/* status, etc and bvec pool number */
 	unsigned short		bi_ioprio;
 	unsigned short		bi_write_hint;
+	DECLARE_BITMAP(bi_rd_hint, BLKDEV_MAX_MIRRORS);
 	blk_status_t		bi_status;
 	u8			bi_partno;
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 0191dc4d3f2d..0a1e93b282c4 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -214,6 +214,7 @@ struct request {
 #endif
 
 	unsigned short write_hint;
+	DECLARE_BITMAP(rd_hint, BLKDEV_MAX_MIRRORS);
 	unsigned short ioprio;
 
 	void *special;		/* opaque pointer available for LLD use */
-- 
2.17.1