On Mon, Mar 24, 2025 at 7:01 AM Jason Wang <jasow...@redhat.com> wrote:
>
> 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: Eugenio Pérez <epere...@redhat.com>
> Signed-off-by: Jason Wang <jasow...@redhat.com>
> ---
> drivers/virtio/virtio_ring.c | 25 +++++++++++++------------
> 1 file changed, 13 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index ce1dc90ee89d..31aa4a935c27 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -561,7 +561,7 @@ 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, c, avail, descs_used, err_idx;
> int head;
> bool indirect;
>
> @@ -617,46 +617,47 @@ static inline int virtqueue_add_split(struct
> vring_virtqueue *vq,
> return -ENOSPC;
> }
>
> + c = 0;
> for (n = 0; n < out_sgs; n++) {
> + sg = sgs[n];
> for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> dma_addr_t addr;
> u32 len;
> + u16 flags = 0;
>
> if (vring_map_one_sg(vq, sg, DMA_TO_DEVICE, &addr,
> &len, premapped))
> goto unmap_release;
>
> - prev = i;
> + if (++c != total_sg)
> + flags = VRING_DESC_F_NEXT;
> +
> /* 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,
> + flags,
> premapped);
> }
> }
> for (; n < (out_sgs + in_sgs); n++) {
> for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> + u16 flags = VRING_DESC_F_WRITE;
> dma_addr_t addr;
> u32 len;
>
> if (vring_map_one_sg(vq, sg, DMA_FROM_DEVICE, &addr,
> &len, premapped))
> goto unmap_release;
>
> - prev = i;
> + if (++c != total_sg)
> + flags |= VRING_DESC_F_NEXT;
> +
> /* 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);
> + 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. */
> --
> 2.42.0
>
