[RFC PATCH 18/28] block: Introduce bio_add_dma_addr()

[Logan Gunthorpe]

bio_add_dma_addr() is analagous to bio_add_page() except it
adds a dma address to a dma-direct bio instead of a struct page.

It also checks to ensure that the queue supports dma address bios and
that we are not mixing dma addresses and struct pages.

Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
---
 block/bio.c         | 38 ++++++++++++++++++++++++++++++++++++++
 include/linux/bio.h | 10 ++++++++++
 2 files changed, 48 insertions(+)

diff --git a/block/bio.c b/block/bio.c
index 6998fceddd36..02ae72e3ccfa 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -874,6 +874,44 @@ static void bio_release_pages(struct bio *bio)
 		put_page(bvec->bv_page);
 }
 
+/**
+ *	bio_add_dma_addr - attempt to add a dma address to a bio
+ *	@q: the target queue
+ *	@bio: destination bio
+ *	@dma_addr: dma address to add
+ *	@len: vec entry length
+ *
+ *	Attempt to add a dma address to the dma_vec maplist. This can
+ *	fail for a number of reasons, such as the bio being full or
+ *	target block device limitations. The target request queue must
+ *	support dma-only bios and bios can not mix pages and dma_addresses.
+ */
+int bio_add_dma_addr(struct request_queue *q, struct bio *bio,
+		     dma_addr_t dma_addr, unsigned int len)
+{
+	struct dma_vec *dv = &bio->bi_dma_vec[bio->bi_vcnt];
+
+	if (!blk_queue_dma_direct(q))
+		return -EINVAL;
+
+	if (!bio_is_dma_direct(bio))
+		return -EINVAL;
+
+	if (bio_dma_full(bio))
+		return 0;
+
+	WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED));
+
+	dv->dv_addr = dma_addr;
+	dv->dv_len = len;
+
+	bio->bi_iter.bi_size += len;
+	bio->bi_vcnt++;
+
+	return len;
+}
+EXPORT_SYMBOL_GPL(bio_add_dma_addr);
+
 static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter)
 {
 	const struct bio_vec *bv = iter->bvec;
diff --git a/include/linux/bio.h b/include/linux/bio.h
index df7973932525..d775f381ae00 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -112,6 +112,13 @@ static inline bool bio_full(struct bio *bio)
 	return bio->bi_vcnt >= bio->bi_max_vecs;
 }
 
+static inline bool bio_dma_full(struct bio *bio)
+{
+	size_t vec_size = bio->bi_max_vecs * sizeof(struct bio_vec);
+
+	return bio->bi_vcnt >= (vec_size / sizeof(struct dma_vec));
+}
+
 static inline bool bio_next_segment(const struct bio *bio,
 				    struct bvec_iter_all *iter)
 {
@@ -438,6 +445,9 @@ void bio_chain(struct bio *, struct bio *);
 extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
 extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
 			   unsigned int, unsigned int);
+extern int bio_add_dma_addr(struct request_queue *q, struct bio *bio,
+			    dma_addr_t dma_addr, unsigned int len);
+
 bool __bio_try_merge_page(struct bio *bio, struct page *page,
 		unsigned int len, unsigned int off, bool same_page);
 void __bio_add_page(struct bio *bio, struct page *page,
-- 
2.20.1