[PATCHv3 1/7] blk-mq: add ops to dma map bvec

[Keith Busch <kbusch@fb.com>]

From: Keith Busch <kbusch@kernel.org>

The same buffer may be used for many subsequent IO's. Instead of setting
up the mapping per-IO, provide an interface that can allow a buffer to be
premapped just once and referenced again later.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 block/bdev.c           | 20 ++++++++++++++++++++
 include/linux/blk-mq.h | 13 +++++++++++++
 include/linux/blkdev.h | 16 ++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/block/bdev.c b/block/bdev.c
index ce05175e71ce..c3d73ad86fae 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -1069,3 +1069,23 @@ void sync_bdevs(bool wait)
 	spin_unlock(&blockdev_superblock->s_inode_list_lock);
 	iput(old_inode);
 }
+
+#ifdef CONFIG_HAS_DMA
+void *block_dma_map(struct block_device *bdev, struct bio_vec *bvec,
+		    int nr_vecs)
+{
+	struct request_queue *q = bdev_get_queue(bdev);
+
+	if (q->mq_ops && q->mq_ops->dma_map)
+		return q->mq_ops->dma_map(q, bvec, nr_vecs);
+	return ERR_PTR(-EINVAL);
+}
+
+void block_dma_unmap(struct block_device *bdev, void *dma_tag)
+{
+	struct request_queue *q = bdev_get_queue(bdev);
+
+	if (q->mq_ops && q->mq_ops->dma_unmap)
+		return q->mq_ops->dma_unmap(q, dma_tag);
+}
+#endif
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index effee1dc715a..e10aabb36c2c 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -639,6 +639,19 @@ struct blk_mq_ops {
 	 */
 	void (*show_rq)(struct seq_file *m, struct request *rq);
 #endif
+
+#ifdef CONFIG_HAS_DMA
+	/**
+	 * @dma_map: Create a dma mapping. On success, returns an opaque cookie
+	 * that the can be referenced by the driver in future requests.
+	 */
+	void *(*dma_map)(struct request_queue *q, struct bio_vec *bvec, int nr_vecs);
+
+	/**
+	 * @dma_unmap: Tear down a previously created dma mapping.
+	 */
+	void (*dma_unmap)(struct request_queue *q, void *dma_tag);
+#endif
 };
 
 enum {
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 49dcd31e283e..efc5e805a46e 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1527,4 +1527,20 @@ struct io_comp_batch {
 
 #define DEFINE_IO_COMP_BATCH(name)	struct io_comp_batch name = { }
 
+#ifdef CONFIG_HAS_DMA
+void *block_dma_map(struct block_device *bdev, struct bio_vec *bvec,
+		    int nr_vecs);
+void block_dma_unmap(struct block_device *bdev, void *dma_tag);
+#else
+static inline void *block_dma_map(struct block_device *bdev,
+				  struct bio_vec *bvec, int nr_vecs)
+{
+	return ERR_PTR(-ENOTSUPP);
+}
+
+static inline void block_dma_unmap(struct block_device *bdev, void *dma_tag)
+{
+}
+#endif
+
 #endif /* _LINUX_BLKDEV_H */
-- 
2.30.2