Re: [PATCH V6 14/19] virtio_ring: determine descriptor flags at one time

On Mon, Sep 22, 2025 at 1:44 AM Michael S. Tsirkin [off-list ref] wrote:

On Fri, Sep 19, 2025 at 03:31:49PM +0800, Jason Wang wrote:

quoted

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 <eperezma@redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Jason Wang <redacted>
---
 drivers/virtio/virtio_ring.c | 21 ++++++++-------------
 1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 1045c553ee65..0949675a3d12 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c

@@ -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, c = 0;
      int head;
      bool indirect;

@@ -631,6 +631,7 @@ static inline int virtqueue_add_split(struct vring_virtqueue *vq,
      }

      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;

How does this make any sense?

Let me drop this unnecessary assignment.

Thanks.