[PATCH v6 12/12] nvme-rdma: factor out the scatterlist DMA mapping helper

[Mykola Marzhan]

The data and the metadata mapping do the same thing: describe the
segments blk_rq_map_sg() produced in a local sg_table -- the embedded
one's orig_nents is the allocated size, not the valid-segment count --
map that, and hand back the DMA-mapped count.  Fold both into a
helper.

No functional change.

Suggested-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Assisted-by: Claude:claude-fable-5
Signed-off-by: Mykola Marzhan <mykola@xxxxxxxxxxx>
---
 drivers/nvme/host/rdma.c | 42 +++++++++++++++++++++++++++-------------
 1 file changed, 29 insertions(+), 13 deletions(-)

diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
index 2f50509a7a61..525e5aea65a1 100644
--- a/drivers/nvme/host/rdma.c
+++ b/drivers/nvme/host/rdma.c
@@ -1465,11 +1465,33 @@ static int nvme_rdma_map_sg_pi(struct nvme_rdma_queue *queue,
 	return -EINVAL;
 }
 
+/*
+ * Map the segments blk_rq_map_sg() produced.  They are described by a local
+ * sg_table because the embedded one's orig_nents is the allocated size, not
+ * the number of valid segments; rdma_rw_ctx_init() does the same.
+ */
+static int nvme_rdma_dma_map_sgl(struct ib_device *ibdev,
+		struct scatterlist *sgl, int nents,
+		enum dma_data_direction dir, int *count)
+{
+	struct sg_table sgt = {
+		.sgl		= sgl,
+		.orig_nents	= nents,
+	};
+	int ret;
+
+	ret = ib_dma_map_sgtable_attrs(ibdev, &sgt, dir, 0);
+	if (unlikely(ret))
+		return ret;
+
+	*count = sgt.nents;
+	return 0;
+}
+
 static int nvme_rdma_dma_map_req(struct ib_device *ibdev, struct request *rq,
 		int *count, int *pi_count)
 {
 	struct nvme_rdma_request *req = blk_mq_rq_to_pdu(rq);
-	struct sg_table sgt;
 	int ret;
 
 	req->data_sgl.sg_table.sgl = (struct scatterlist *)(req + 1);
@@ -1481,14 +1503,10 @@ static int nvme_rdma_dma_map_req(struct ib_device *ibdev, struct request *rq,
 
 	req->data_sgl.nents = blk_rq_map_sg(rq, req->data_sgl.sg_table.sgl);
 
-	sgt = (struct sg_table) {
-		.sgl		= req->data_sgl.sg_table.sgl,
-		.orig_nents	= req->data_sgl.nents,
-	};
-	ret = ib_dma_map_sgtable_attrs(ibdev, &sgt, rq_dma_dir(rq), 0);
+	ret = nvme_rdma_dma_map_sgl(ibdev, req->data_sgl.sg_table.sgl,
+				    req->data_sgl.nents, rq_dma_dir(rq), count);
 	if (unlikely(ret))
 		goto out_free_table;
-	*count = sgt.nents;
 
 	if (blk_integrity_rq(rq)) {
 		req->metadata_sgl->sg_table.sgl =
@@ -1504,14 +1522,12 @@ static int nvme_rdma_dma_map_req(struct ib_device *ibdev, struct request *rq,
 
 		req->metadata_sgl->nents = blk_rq_map_integrity_sg(rq,
 				req->metadata_sgl->sg_table.sgl);
-		sgt = (struct sg_table) {
-			.sgl		= req->metadata_sgl->sg_table.sgl,
-			.orig_nents	= req->metadata_sgl->nents,
-		};
-		ret = ib_dma_map_sgtable_attrs(ibdev, &sgt, rq_dma_dir(rq), 0);
+		ret = nvme_rdma_dma_map_sgl(ibdev,
+					    req->metadata_sgl->sg_table.sgl,
+					    req->metadata_sgl->nents,
+					    rq_dma_dir(rq), pi_count);
 		if (unlikely(ret))
 			goto out_free_pi_table;
-		*pi_count = sgt.nents;
 	}
 
 	return 0;
-- 
2.52.0