virtio_ring: introduce virtqueue_desc_add_split()

This patch introduces a helper for storing descriptor in the
descriptor table for split virtqueue.
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210604055350.58753-6-jasowang@redhat.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_ring.c

@@ -415,6 +415,20 @@ static struct vring_desc *alloc_indirect_split(struct virtqueue *_vq,
 	return desc;
 }
 
+static inline unsigned int virtqueue_add_desc_split(struct virtqueue *vq,
+						    struct vring_desc *desc,
+						    unsigned int i,
+						    dma_addr_t addr,
+						    unsigned int len,
+						    u16 flags)
+{
+	desc[i].flags = cpu_to_virtio16(vq->vdev, flags);
+	desc[i].addr = cpu_to_virtio64(vq->vdev, addr);
+	desc[i].len = cpu_to_virtio32(vq->vdev, len);
+
+	return virtio16_to_cpu(vq->vdev, desc[i].next);
+}
+
 static inline int virtqueue_add_split(struct virtqueue *_vq,
 				      struct scatterlist *sgs[],
 				      unsigned int total_sg,
@@ -487,11 +501,9 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 			if (vring_mapping_error(vq, addr))
 				goto unmap_release;
 
-			desc[i].flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT);
-			desc[i].addr = cpu_to_virtio64(_vq->vdev, addr);
-			desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length);
 			prev = i;
-			i = virtio16_to_cpu(_vq->vdev, desc[i].next);
+			i = virtqueue_add_desc_split(_vq, desc, i, addr, sg->length,
+						     VRING_DESC_F_NEXT);
 		}
 	}
 	for (; n < (out_sgs + in_sgs); n++) {
@@ -500,11 +512,11 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 			if (vring_mapping_error(vq, addr))
 				goto unmap_release;
 
-			desc[i].flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT | VRING_DESC_F_WRITE);
-			desc[i].addr = cpu_to_virtio64(_vq->vdev, addr);
-			desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length);
 			prev = i;
-			i = virtio16_to_cpu(_vq->vdev, desc[i].next);
+			i = virtqueue_add_desc_split(_vq, desc, i, addr,
+						     sg->length,
+						     VRING_DESC_F_NEXT |
+						     VRING_DESC_F_WRITE);
 		}
 	}
 	/* Last one doesn't continue. */
@@ -518,13 +530,10 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 		if (vring_mapping_error(vq, addr))
 			goto unmap_release;
 
-		vq->split.vring.desc[head].flags = cpu_to_virtio16(_vq->vdev,
-				VRING_DESC_F_INDIRECT);
-		vq->split.vring.desc[head].addr = cpu_to_virtio64(_vq->vdev,
-				addr);
-
-		vq->split.vring.desc[head].len = cpu_to_virtio32(_vq->vdev,
-				total_sg * sizeof(struct vring_desc));
+		virtqueue_add_desc_split(_vq, vq->split.vring.desc,
+					 head, addr,
+					 total_sg * sizeof(struct vring_desc),
+			                 VRING_DESC_F_INDIRECT);
 	}
 
 	/* We're using some buffers from the free list. */