RDMA/core: add bio_vec based RDMA read/write API

The existing rdma_rw_ctx_init() API requires callers to construct a
scatterlist, which is then DMA-mapped page by page. Callers that
already have data in bio_vec form (such as the NVMe-oF target) must
first convert to scatterlist, adding overhead and complexity.

Introduce rdma_rw_ctx_init_bvec() and rdma_rw_ctx_destroy_bvec() to
accept bio_vec arrays directly. The new helpers use dma_map_phys()
for hardware RDMA devices and virtual addressing for software RDMA
devices (rxe, siw), avoiding intermediate scatterlist construction.

Memory registration (MR) path support is deferred to a follow-up
series; callers requiring MR-based transfers (iWARP devices or
force_mr=1) receive -EOPNOTSUPP and should use the scatterlist API.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://patch.msgid.link/20260128005400.25147-2-cel@kernel.org
Signed-off-by: Leon Romanovsky <leon@kernel.org>

2 files changed, 53 insertions, 0 deletions

diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index 6c372a37c482..8bd020da7745 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -15,6 +15,7 @@
 #include <linux/ethtool.h>
 #include <linux/types.h>
 #include <linux/device.h>
+#include <linux/bvec.h>
 #include <linux/dma-mapping.h>
 #include <linux/kref.h>
 #include <linux/list.h>
@@ -4266,6 +4267,47 @@ static inline void ib_dma_unmap_page(struct ib_device *dev,
 		dma_unmap_page(dev->dma_device, addr, size, direction);
 }
 
+/**
+ * ib_dma_map_bvec - Map a bio_vec to DMA address
+ * @dev: The device for which the dma_addr is to be created
+ * @bvec: The bio_vec to map
+ * @direction: The direction of the DMA
+ *
+ * Returns a DMA address for the bio_vec. The caller must check the
+ * result with ib_dma_mapping_error() before use; a failed mapping
+ * must not be passed to ib_dma_unmap_bvec().
+ *
+ * For software RDMA devices (rxe, siw), returns a virtual address
+ * and no actual DMA mapping occurs.
+ */
+static inline u64 ib_dma_map_bvec(struct ib_device *dev,
+				  struct bio_vec *bvec,
+				  enum dma_data_direction direction)
+{
+	if (ib_uses_virt_dma(dev))
+		return (uintptr_t)bvec_virt(bvec);
+	return dma_map_phys(dev->dma_device, bvec_phys(bvec),
+			    bvec->bv_len, direction, 0);
+}
+
+/**
+ * ib_dma_unmap_bvec - Unmap a bio_vec DMA mapping
+ * @dev: The device for which the DMA address was created
+ * @addr: The DMA address returned by ib_dma_map_bvec()
+ * @size: The size of the region in bytes
+ * @direction: The direction of the DMA
+ *
+ * Releases a DMA mapping created by ib_dma_map_bvec(). For software
+ * RDMA devices this is a no-op since no actual mapping occurred.
+ */
+static inline void ib_dma_unmap_bvec(struct ib_device *dev,
+				     u64 addr, size_t size,
+				     enum dma_data_direction direction)
+{
+	if (!ib_uses_virt_dma(dev))
+		dma_unmap_phys(dev->dma_device, addr, size, direction, 0);
+}
+
 int ib_dma_virt_map_sg(struct ib_device *dev, struct scatterlist *sg, int nents);
 static inline int ib_dma_map_sg_attrs(struct ib_device *dev,
 				      struct scatterlist *sg, int nents,
diff --git a/include/rdma/rw.h b/include/rdma/rw.h
index d606cac48233..b2fc3e2373d7 100644
--- a/include/rdma/rw.h
+++ b/include/rdma/rw.h
@@ -5,6 +5,7 @@
 #ifndef _RDMA_RW_H
 #define _RDMA_RW_H
 
+#include <linux/bvec.h>
 #include <linux/dma-mapping.h>
 #include <linux/scatterlist.h>
 #include <rdma/ib_verbs.h>
@@ -49,6 +50,16 @@ void rdma_rw_ctx_destroy(struct rdma_rw_ctx *ctx, struct ib_qp *qp,
 			 u32 port_num, struct scatterlist *sg, u32 sg_cnt,
 			 enum dma_data_direction dir);
 
+struct bio_vec;
+
+int rdma_rw_ctx_init_bvec(struct rdma_rw_ctx *ctx, struct ib_qp *qp,
+		u32 port_num, const struct bio_vec *bvecs, u32 nr_bvec,
+		struct bvec_iter iter, u64 remote_addr, u32 rkey,
+		enum dma_data_direction dir);
+void rdma_rw_ctx_destroy_bvec(struct rdma_rw_ctx *ctx, struct ib_qp *qp,
+		u32 port_num, const struct bio_vec *bvecs, u32 nr_bvec,
+		enum dma_data_direction dir);
+
 int rdma_rw_ctx_signature_init(struct rdma_rw_ctx *ctx, struct ib_qp *qp,
 		u32 port_num, struct scatterlist *sg, u32 sg_cnt,
 		struct scatterlist *prot_sg, u32 prot_sg_cnt,