Commit 03f05c4e authored by Jason Wang's avatar Jason Wang Committed by Michael S. Tsirkin
Browse files

virtio_ring: determine descriptor flags at one time 



Let's determine the last descriptor by counting the number of sg. This
would be consistent with packed virtqueue implementation and ease the
future in-order implementation.

Acked-by: default avatarEugenio Pérez <eperezma@redhat.com>
Reviewed-by: default avatarXuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: default avatarJason Wang <jasowang@redhat.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Message-Id: <20251230064649.55597-15-jasowang@redhat.com>
parent 1208473f

drivers/virtio/virtio_ring.c

+13 −15
Original line number Diff line number Diff line
@@ -574,7 +574,7 @@ static inline int virtqueue_add_split(struct vring_virtqueue *vq, 
	struct vring_desc_extra *extra;

	struct scatterlist *sg;

	struct vring_desc *desc;

	unsigned int i, n, avail, descs_used, prev, err_idx;

	unsigned int i, n, avail, descs_used, err_idx, sg_count = 0;

	int head;

	bool indirect;
@@ -634,42 +634,40 @@ static inline int virtqueue_add_split(struct vring_virtqueue *vq, 
		for (sg = sgs[n]; sg; sg = sg_next(sg)) {

			dma_addr_t addr;

			u32 len;

			u16 flags = 0;



			if (++sg_count != total_sg)

				flags |= VRING_DESC_F_NEXT;



			if (vring_map_one_sg(vq, sg, DMA_TO_DEVICE, &addr, &len, premapped))

				goto unmap_release;



			prev = i;

			/* Note that we trust indirect descriptor

			 * table since it use stream DMA mapping.

			 */

			i = virtqueue_add_desc_split(vq, desc, extra, i, addr, len,

						     VRING_DESC_F_NEXT,

						     premapped);

			i = virtqueue_add_desc_split(vq, desc, extra, i, addr,

						     len, flags, premapped);

		}

	}

	for (; n < (out_sgs + in_sgs); n++) {

		for (sg = sgs[n]; sg; sg = sg_next(sg)) {

			dma_addr_t addr;

			u32 len;

			u16 flags = VRING_DESC_F_WRITE;



			if (++sg_count != total_sg)

				flags |= VRING_DESC_F_NEXT;



			if (vring_map_one_sg(vq, sg, DMA_FROM_DEVICE, &addr, &len, premapped))

				goto unmap_release;



			prev = i;

			/* Note that we trust indirect descriptor

			 * table since it use stream DMA mapping.

			 */

			i = virtqueue_add_desc_split(vq, desc, extra, i, addr, len,

						     VRING_DESC_F_NEXT |

						     VRING_DESC_F_WRITE,

						     premapped);

			i = virtqueue_add_desc_split(vq, desc, extra, i, addr,

						     len, flags, premapped);

		}

	}

	/* Last one doesn't continue. */

	desc[prev].flags &= cpu_to_virtio16(vq->vq.vdev, ~VRING_DESC_F_NEXT);

	if (!indirect && vring_need_unmap_buffer(vq, &extra[prev]))

		vq->split.desc_extra[prev & (vq->split.vring.num - 1)].flags &=

			~VRING_DESC_F_NEXT;



	if (indirect) {

		/* Now that the indirect table is filled in, map it. */