[PATCH v2 4/5] block: map dma-buf iterators in blk_rq_map_user_iov()

[Anuj Gupta <anuj1072538@gmail.com>]

From: Anuj Gupta <anuj20.g@samsung.com>

A dma-buf iterator can't fall back to a bounce copy, so map it directly
with blk_rq_map_user_bvec(), which already handles it through
bio_iov_iter_set(). Fail with -EINVAL where a copy would otherwise be
needed, and update the blk_rq_map_user_bvec() comment to match.

Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
---
 block/blk-map.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/block/blk-map.c b/block/blk-map.c
index 9cb9605d1f62..d1e096fdb03d 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -459,7 +459,7 @@ int blk_rq_append_bio(struct request *rq, struct bio *bio)
 }
 EXPORT_SYMBOL(blk_rq_append_bio);
 
-/* Prepare bio for passthrough IO given ITER_BVEC iter */
+/* Prepare a bio for passthrough I/O from a directly mapped iterator. */
 static int blk_rq_map_user_bvec(struct request *rq, const struct iov_iter *iter)
 {
 	unsigned int max_bytes = rq->q->limits.max_hw_sectors << SECTOR_SHIFT;
@@ -506,6 +506,19 @@ int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
 	struct iov_iter i;
 	int ret = -EINVAL;
 
+	if (iov_iter_is_dmabuf_map(iter)) {
+		if (map_data || (iov_iter_alignment(iter) & align))
+			return -EINVAL;
+		ret = blk_rq_map_user_bvec(rq, iter);
+		/*
+		 * -EREMOTEIO asks the caller to fall back to a bounce copy,
+		 * which a dma-buf can't do.
+		 */
+		if (ret == -EREMOTEIO)
+			ret = -EINVAL;
+		return ret;
+	}
+
 	if (map_data)
 		copy = true;
 	else if (iov_iter_alignment(iter) & align)
-- 
2.43.0