[RFC PATCH 02/28] block: Add dma_vec structure

[Logan Gunthorpe]

The dma_vec structure is similar to the bio_vec structure except
it only stores DMA addresses instead of the struct page address.

struct bios will be able to make use of dma_vecs with a union and,
therefore, we need to ensure that struct dma_vec is no larger
than struct bvec, as they will share the allocated memory.

dma_vecs can make the same use of the bvec_iter structure
to iterate through the vectors.

This will be used for passing DMA addresses directly through the block
layer. I expect something like struct dma_vec will also be used in
Christoph's work to improve the dma_mapping layer and remove sgls.
At some point, these would use the same structure.

Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
---
 include/linux/bio.h       | 12 +++++++++++
 include/linux/blk_types.h |  5 ++++-
 include/linux/bvec.h      | 43 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 0f23b5682640..8180309123d7 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -28,6 +28,8 @@
 
 #define bio_iter_iovec(bio, iter)				\
 	bvec_iter_bvec((bio)->bi_io_vec, (iter))
+#define bio_iter_dma_vec(bio, iter)				\
+	bvec_iter_dvec((bio)->bi_dma_vec, (iter))
 
 #define bio_iter_page(bio, iter)				\
 	bvec_iter_page((bio)->bi_io_vec, (iter))
@@ -39,6 +41,7 @@
 #define bio_page(bio)		bio_iter_page((bio), (bio)->bi_iter)
 #define bio_offset(bio)		bio_iter_offset((bio), (bio)->bi_iter)
 #define bio_iovec(bio)		bio_iter_iovec((bio), (bio)->bi_iter)
+#define bio_dma_vec(bio)	bio_iter_dma_vec((bio), (bio)->bi_iter)
 
 #define bio_multiple_segments(bio)				\
 	((bio)->bi_iter.bi_size != bio_iovec(bio).bv_len)
@@ -155,6 +158,15 @@ static inline void bio_advance_iter(struct bio *bio, struct bvec_iter *iter,
 #define bio_for_each_bvec(bvl, bio, iter)			\
 	__bio_for_each_bvec(bvl, bio, iter, (bio)->bi_iter)
 
+#define __bio_for_each_dvec(dvl, bio, iter, start)		\
+	for (iter = (start);						\
+	     (iter).bi_size &&						\
+		((dvl = bvec_iter_dvec((bio)->bi_dma_vec, (iter))), 1); \
+	     dvec_iter_advance((bio)->bi_dma_vec, &(iter), (dvl).dv_len))
+
+#define bio_for_each_dvec(dvl, bio, iter)			\
+	__bio_for_each_dvec(dvl, bio, iter, (bio)->bi_iter)
+
 #define bio_iter_last(bvec, iter) ((iter).bi_size == (bvec).bv_len)
 
 static inline unsigned bio_segments(struct bio *bio)
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index f3cabfdb6774..7f76ea73b77d 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -191,7 +191,10 @@ 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 */
+		struct dma_vec	*bi_dma_vec;	/* for dma direct bios*/
+	};
 
 	struct bio_set		*bi_pool;
 
diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index a032f01e928c..f680e96132ef 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -21,6 +21,11 @@ struct bio_vec {
 	unsigned int	bv_offset;
 };
 
+struct dma_vec {
+	dma_addr_t	dv_addr;
+	unsigned int	dv_len;
+};
+
 struct bvec_iter {
 	sector_t		bi_sector;	/* device address in 512 byte
 						   sectors */
@@ -84,6 +89,18 @@ struct bvec_iter_all {
 	.bv_offset	= bvec_iter_offset((bvec), (iter)),	\
 })
 
+#define bvec_iter_dvec_addr(dvec, iter)	\
+	(__bvec_iter_bvec((dvec), (iter))->dv_addr + (iter).bi_bvec_done)
+#define bvec_iter_dvec_len(dvec, iter)	\
+	min((iter).bi_size,					\
+	    __bvec_iter_bvec((dvec), (iter))->dv_len - (iter).bi_bvec_done)
+
+#define bvec_iter_dvec(dvec, iter)				\
+((struct dma_vec) {						\
+	.dv_addr	= bvec_iter_dvec_addr((dvec), (iter)),	\
+	.dv_len		= bvec_iter_dvec_len((dvec), (iter)),	\
+})
+
 static inline bool bvec_iter_advance(const struct bio_vec *bv,
 		struct bvec_iter *iter, unsigned bytes)
 {
@@ -110,6 +127,32 @@ static inline bool bvec_iter_advance(const struct bio_vec *bv,
 	return true;
 }
 
+static inline bool dvec_iter_advance(const struct dma_vec *dv,
+		struct bvec_iter *iter, unsigned bytes)
+{
+	if (WARN_ONCE(bytes > iter->bi_size,
+		      "Attempted to advance past end of dvec iter\n")) {
+		iter->bi_size = 0;
+		return false;
+	}
+
+	while (bytes) {
+		const struct dma_vec *cur = dv + iter->bi_idx;
+		unsigned len = min3(bytes, iter->bi_size,
+				    cur->dv_len - iter->bi_bvec_done);
+
+		bytes -= len;
+		iter->bi_size -= len;
+		iter->bi_bvec_done += len;
+
+		if (iter->bi_bvec_done == cur->dv_len) {
+			iter->bi_bvec_done = 0;
+			iter->bi_idx++;
+		}
+	}
+	return true;
+}
+
 #define for_each_bvec(bvl, bio_vec, iter, start)			\
 	for (iter = (start);						\
 	     (iter).bi_size &&						\
-- 
2.20.1