[PATCHv2 4/7] block: add dma tag bio type

[Keith Busch <kbusch@fb.com>]

From: Keith Busch <kbusch@kernel.org>

Premapped buffers don't require a generic bio_vec since these have
already been dma mapped to the driver specific data structure. Repurpose
the bi_io_vec with the driver specific tag as they are mutually
exclusive, and provide all the setup and split helpers to support dma
tags.

In order to use this, a driver must implement the .dma_map() blk-mq op..
If the driver provides this callback, then it must be aware that any
given bio may be using a dma_tag instead of a bio_vec.

Note, this isn't working with blk_integrity.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 block/bio.c               | 25 ++++++++++++++++++++++++-
 block/blk-merge.c         | 19 +++++++++++++++++++
 include/linux/bio.h       | 21 ++++++++++++---------
 include/linux/blk-mq.h    | 11 +++++++++++
 include/linux/blk_types.h |  6 +++++-
 5 files changed, 71 insertions(+), 11 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index d6eb90d9b20b..3b7accae8996 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -229,7 +229,8 @@ static void bio_free(struct bio *bio)
 	WARN_ON_ONCE(!bs);
 
 	bio_uninit(bio);
-	bvec_free(&bs->bvec_pool, bio->bi_io_vec, bio->bi_max_vecs);
+	if (!bio_flagged(bio, BIO_DMA_TAGGED))
+		bvec_free(&bs->bvec_pool, bio->bi_io_vec, bio->bi_max_vecs);
 	mempool_free(p - bs->front_pad, &bs->bio_pool);
 }
 
@@ -762,6 +763,8 @@ static int __bio_clone(struct bio *bio, struct bio *bio_src, gfp_t gfp)
 	bio_set_flag(bio, BIO_CLONED);
 	if (bio_flagged(bio_src, BIO_THROTTLED))
 		bio_set_flag(bio, BIO_THROTTLED);
+	if (bio_flagged(bio_src, BIO_DMA_TAGGED))
+		bio_set_flag(bio, BIO_DMA_TAGGED);
 	bio->bi_ioprio = bio_src->bi_ioprio;
 	bio->bi_iter = bio_src->bi_iter;
 
@@ -1151,6 +1154,21 @@ void bio_iov_bvec_set(struct bio *bio, struct iov_iter *iter)
 	bio_set_flag(bio, BIO_CLONED);
 }
 
+static void bio_iov_dma_tag_set(struct bio *bio, struct iov_iter *iter)
+{
+	size_t size = iov_iter_count(iter);
+
+	bio->bi_vcnt = iter->nr_segs;
+	bio->bi_dma_tag = iter->dma_tag;
+	bio->bi_iter.bi_bvec_done = iter->iov_offset;
+	bio->bi_iter.bi_size = size;
+	bio->bi_opf |= REQ_NOMERGE;
+	bio_set_flag(bio, BIO_NO_PAGE_REF);
+	bio_set_flag(bio, BIO_DMA_TAGGED);
+
+	iov_iter_advance(iter, bio->bi_iter.bi_size);
+}
+
 static int bio_iov_add_page(struct bio *bio, struct page *page,
 		unsigned int len, unsigned int offset)
 {
@@ -1287,6 +1305,11 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 		return 0;
 	}
 
+	if (iov_iter_is_dma_tag(iter)) {
+		bio_iov_dma_tag_set(bio, iter);
+		return 0;
+	}
+
 	do {
 		ret = __bio_iov_iter_get_pages(bio, iter);
 	} while (!ret && iov_iter_count(iter) && !bio_full(bio, 0));
diff --git a/block/blk-merge.c b/block/blk-merge.c
index ff04e9290715..d024885ad4c4 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -274,6 +274,25 @@ static struct bio *bio_split_rw(struct bio *bio, struct queue_limits *lim,
 	struct bvec_iter iter;
 	unsigned nsegs = 0, bytes = 0;
 
+	if (bio_flagged(bio, BIO_DMA_TAGGED)) {
+		int offset = offset_in_page(bio->bi_iter.bi_bvec_done);
+
+		nsegs = ALIGN(bio->bi_iter.bi_size + offset, PAGE_SIZE) >>
+								PAGE_SHIFT;
+		if (bio->bi_iter.bi_size > max_bytes) {
+			bytes = max_bytes;
+			nsegs = (bytes + offset) >> PAGE_SHIFT;
+		} else if (nsegs > lim->max_segments) {
+			nsegs = lim->max_segments;
+			bytes = PAGE_SIZE * nsegs - offset;
+		} else {
+			*segs = nsegs;
+			return NULL;
+		}
+
+		goto split;
+	}
+
 	bio_for_each_bvec(bv, bio, iter) {
 		/*
 		 * If the queue doesn't support SG gaps and adding this
diff --git a/include/linux/bio.h b/include/linux/bio.h
index ca22b06700a9..649348bc03c2 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -61,11 +61,17 @@ static inline bool bio_has_data(struct bio *bio)
 	return false;
 }
 
+static inline bool bio_flagged(const struct bio *bio, unsigned int bit)
+{
+	return (bio->bi_flags & (1U << bit)) != 0;
+}
+
 static inline bool bio_no_advance_iter(const struct bio *bio)
 {
 	return bio_op(bio) == REQ_OP_DISCARD ||
 	       bio_op(bio) == REQ_OP_SECURE_ERASE ||
-	       bio_op(bio) == REQ_OP_WRITE_ZEROES;
+	       bio_op(bio) == REQ_OP_WRITE_ZEROES ||
+	       bio_flagged(bio, BIO_DMA_TAGGED);
 }
 
 static inline void *bio_data(struct bio *bio)
@@ -98,9 +104,11 @@ static inline void bio_advance_iter(const struct bio *bio,
 {
 	iter->bi_sector += bytes >> 9;
 
-	if (bio_no_advance_iter(bio))
+	if (bio_no_advance_iter(bio)) {
 		iter->bi_size -= bytes;
-	else
+		if (bio_flagged(bio, BIO_DMA_TAGGED))
+			iter->bi_bvec_done += bytes;
+	} else
 		bvec_iter_advance(bio->bi_io_vec, iter, bytes);
 		/* TODO: It is reasonable to complete bio with error here. */
 }
@@ -225,11 +233,6 @@ static inline void bio_cnt_set(struct bio *bio, unsigned int count)
 	atomic_set(&bio->__bi_cnt, count);
 }
 
-static inline bool bio_flagged(struct bio *bio, unsigned int bit)
-{
-	return (bio->bi_flags & (1U << bit)) != 0;
-}
-
 static inline void bio_set_flag(struct bio *bio, unsigned int bit)
 {
 	bio->bi_flags |= (1U << bit);
@@ -447,7 +450,7 @@ static inline void bio_wouldblock_error(struct bio *bio)
  */
 static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs)
 {
-	if (iov_iter_is_bvec(iter))
+	if (iov_iter_is_bvec(iter) || iov_iter_is_dma_tag(iter))
 		return 0;
 	return iov_iter_npages(iter, max_segs);
 }
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index e10aabb36c2c..f5e0aa61bf85 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -1141,6 +1141,17 @@ static inline int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 }
 void blk_dump_rq_flags(struct request *, char *);
 
+static inline void *blk_rq_dma_tag(struct request *rq)
+{
+	return rq->bio && bio_flagged(rq->bio, BIO_DMA_TAGGED) ?
+		rq->bio->bi_dma_tag : 0;
+}
+
+static inline size_t blk_rq_dma_offset(struct request *rq)
+{
+	return rq->bio->bi_iter.bi_bvec_done;
+}
+
 #ifdef CONFIG_BLK_DEV_ZONED
 static inline unsigned int blk_rq_zone_no(struct request *rq)
 {
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 1ef99790f6ed..ea6db439acbe 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -299,7 +299,10 @@ struct bio {
 
 	atomic_t		__bi_cnt;	/* pin count */
 
-	struct bio_vec		*bi_io_vec;	/* the actual vec list */
+	union {
+		struct bio_vec		*bi_io_vec;	/* the actual vec list */
+		void			*bi_dma_tag;    /* driver specific tag */
+	};
 
 	struct bio_set		*bi_pool;
 
@@ -334,6 +337,7 @@ enum {
 	BIO_QOS_MERGED,		/* but went through rq_qos merge path */
 	BIO_REMAPPED,
 	BIO_ZONE_WRITE_LOCKED,	/* Owns a zoned device zone write lock */
+	BIO_DMA_TAGGED,		/* Using premmaped dma buffers */
 	BIO_FLAG_LAST
 };
 
-- 
2.30.2