nvme-rdma: introduce nvme_rdma_sgl structure

Remove first_sgl pointer from struct nvme_rdma_request and use pointer
arithmetic instead. The inline scatterlist, if exists, will be located
right after the nvme_rdma_request. This patch is needed as a preparation
for adding PI support.
Signed-off-by: Israel Rukshin <israelr@mellanox.com>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/rdma.c

@@ -48,6 +48,11 @@ struct nvme_rdma_qe {
 	u64			dma;
 };
 
+struct nvme_rdma_sgl {
+	int			nents;
+	struct sg_table		sg_table;
+};
+
 struct nvme_rdma_queue;
 struct nvme_rdma_request {
 	struct nvme_request	req;
@@ -58,12 +63,10 @@ struct nvme_rdma_request {
 	refcount_t		ref;
 	struct ib_sge		sge[1 + NVME_RDMA_MAX_INLINE_SEGMENTS];
 	u32			num_sge;
-	int			nents;
 	struct ib_reg_wr	reg_wr;
 	struct ib_cqe		reg_cqe;
 	struct nvme_rdma_queue  *queue;
-	struct sg_table		sg_table;
-	struct scatterlist	first_sgl[];
+	struct nvme_rdma_sgl	data_sgl;
 };
 
 enum nvme_rdma_queue_flags {
@@ -1158,8 +1161,9 @@ static void nvme_rdma_unmap_data(struct nvme_rdma_queue *queue,
 		req->mr = NULL;
 	}
 
-	ib_dma_unmap_sg(ibdev, req->sg_table.sgl, req->nents, rq_dma_dir(rq));
-	sg_free_table_chained(&req->sg_table, NVME_INLINE_SG_CNT);
+	ib_dma_unmap_sg(ibdev, req->data_sgl.sg_table.sgl, req->data_sgl.nents,
+			rq_dma_dir(rq));
+	sg_free_table_chained(&req->data_sgl.sg_table, NVME_INLINE_SG_CNT);
 }
 
 static int nvme_rdma_set_sg_null(struct nvme_command *c)
@@ -1178,7 +1182,7 @@ static int nvme_rdma_map_sg_inline(struct nvme_rdma_queue *queue,
 		int count)
 {
 	struct nvme_sgl_desc *sg = &c->common.dptr.sgl;
-	struct scatterlist *sgl = req->sg_table.sgl;
+	struct scatterlist *sgl = req->data_sgl.sg_table.sgl;
 	struct ib_sge *sge = &req->sge[1];
 	u32 len = 0;
 	int i;
@@ -1203,8 +1207,8 @@ static int nvme_rdma_map_sg_single(struct nvme_rdma_queue *queue,
 {
 	struct nvme_keyed_sgl_desc *sg = &c->common.dptr.ksgl;
 
-	sg->addr = cpu_to_le64(sg_dma_address(req->sg_table.sgl));
-	put_unaligned_le24(sg_dma_len(req->sg_table.sgl), sg->length);
+	sg->addr = cpu_to_le64(sg_dma_address(req->data_sgl.sg_table.sgl));
+	put_unaligned_le24(sg_dma_len(req->data_sgl.sg_table.sgl), sg->length);
 	put_unaligned_le32(queue->device->pd->unsafe_global_rkey, sg->key);
 	sg->type = NVME_KEY_SGL_FMT_DATA_DESC << 4;
 	return 0;
@@ -1225,7 +1229,8 @@ static int nvme_rdma_map_sg_fr(struct nvme_rdma_queue *queue,
 	 * Align the MR to a 4K page size to match the ctrl page size and
 	 * the block virtual boundary.
 	 */
-	nr = ib_map_mr_sg(req->mr, req->sg_table.sgl, count, NULL, SZ_4K);
+	nr = ib_map_mr_sg(req->mr, req->data_sgl.sg_table.sgl, count, NULL,
+			  SZ_4K);
 	if (unlikely(nr < count)) {
 		ib_mr_pool_put(queue->qp, &queue->qp->rdma_mrs, req->mr);
 		req->mr = NULL;
@@ -1272,17 +1277,18 @@ static int nvme_rdma_map_data(struct nvme_rdma_queue *queue,
 	if (!blk_rq_nr_phys_segments(rq))
 		return nvme_rdma_set_sg_null(c);
 
-	req->sg_table.sgl = req->first_sgl;
-	ret = sg_alloc_table_chained(&req->sg_table,
-			blk_rq_nr_phys_segments(rq), req->sg_table.sgl,
+	req->data_sgl.sg_table.sgl = (struct scatterlist *)(req + 1);
+	ret = sg_alloc_table_chained(&req->data_sgl.sg_table,
+			blk_rq_nr_phys_segments(rq), req->data_sgl.sg_table.sgl,
 			NVME_INLINE_SG_CNT);
 	if (ret)
 		return -ENOMEM;
 
-	req->nents = blk_rq_map_sg(rq->q, rq, req->sg_table.sgl);
+	req->data_sgl.nents = blk_rq_map_sg(rq->q, rq,
+					    req->data_sgl.sg_table.sgl);
 
-	count = ib_dma_map_sg(ibdev, req->sg_table.sgl, req->nents,
-			      rq_dma_dir(rq));
+	count = ib_dma_map_sg(ibdev, req->data_sgl.sg_table.sgl,
+			      req->data_sgl.nents, rq_dma_dir(rq));
 	if (unlikely(count <= 0)) {
 		ret = -EIO;
 		goto out_free_table;
@@ -1311,9 +1317,10 @@ static int nvme_rdma_map_data(struct nvme_rdma_queue *queue,
 	return 0;
 
 out_unmap_sg:
-	ib_dma_unmap_sg(ibdev, req->sg_table.sgl, req->nents, rq_dma_dir(rq));
+	ib_dma_unmap_sg(ibdev, req->data_sgl.sg_table.sgl, req->data_sgl.nents,
+			rq_dma_dir(rq));
 out_free_table:
-	sg_free_table_chained(&req->sg_table, NVME_INLINE_SG_CNT);
+	sg_free_table_chained(&req->data_sgl.sg_table, NVME_INLINE_SG_CNT);
 	return ret;
 }