Re: [PATCH v2 02/12] virtio_ring: Add helper to attach vring descriptor

On Wed, Apr 13, 2022 at 10:22 PM Andrew Scull ascull@google.com wrote:

Move the logic for attaching a descriptor to its own function.

Signed-off-by: Andrew Scull ascull@google.com Reviewed-by: Simon Glass sjg@chromium.org

---

drivers/virtio/virtio_ring.c | 30 +++++++++++++++--------------- 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index a6922ce1b8..8e0cb3d666 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -16,6 +16,18 @@ #include <linux/bug.h> #include <linux/compat.h>

+static unsigned int virtqueue_attach_desc(struct virtqueue *vq, unsigned int i,

•                                     struct virtio_sg *sg, u16 flags)
  

+{

•   struct vring_desc *desc = &vq->vring.desc[i];
  

•   desc->addr = cpu_to_virtio64(vq->vdev, (u64)(uintptr_t)sg->addr);
  

•   desc->len = cpu_to_virtio32(vq->vdev, sg->length);
  

•   desc->flags = cpu_to_virtio16(vq->vdev, flags);
  

•   return virtio16_to_cpu(vq->vdev, desc->next);
  

+}

int virtqueue_add(struct virtqueue *vq, struct virtio_sg *sgs[], unsigned int out_sgs, unsigned int in_sgs) { @@ -45,26 +57,14 @@ int virtqueue_add(struct virtqueue *vq, struct virtio_sg *sgs[], }

    for (n = 0; n < out_sgs; n++) {

•           struct virtio_sg *sg = sgs[n];
  

•           desc[i].flags = cpu_to_virtio16(vq->vdev, VRING_DESC_F_NEXT);
  

•           desc[i].addr = cpu_to_virtio64(vq->vdev, (u64)(size_t)sg->addr);
  

•           desc[i].len = cpu_to_virtio32(vq->vdev, sg->length);
  

•           prev = i;
  

•           i = virtio16_to_cpu(vq->vdev, desc[i].next);
  

•           i = virtqueue_attach_desc(vq, i, sgs[n], VRING_DESC_F_NEXT);
    }
    for (; n < (out_sgs + in_sgs); n++) {
  

•           struct virtio_sg *sg = sgs[n];
  

•           desc[i].flags = cpu_to_virtio16(vq->vdev, VRING_DESC_F_NEXT |
  

•                                           VRING_DESC_F_WRITE);
  

•           desc[i].addr = cpu_to_virtio64(vq->vdev,
  

•                                          (u64)(uintptr_t)sg->addr);
  

•           desc[i].len = cpu_to_virtio32(vq->vdev, sg->length);
  

•           u16 flags = VRING_DESC_F_NEXT | VRING_DESC_F_WRITE;
  
            prev = i;
  

•           i = virtio16_to_cpu(vq->vdev, desc[i].next);
  

•           i = virtqueue_attach_desc(vq, i, sgs[n], flags);
  

The above 2 for loops can be further merged into one loop:

u16 flags = VRING_DESC_F_NEXT; for (n = 0; n < (out_sgs + in_sgs); n++) { if (n >= out_sgs) flags |= VRING_DESC_F_WRITE; prev = i; i = virtqueue_attach_desc(vq, i, sgs[n], flags); }

    }
    /* Last one doesn't continue */
    desc[prev].flags &= cpu_to_virtio16(vq->vdev, ~VRING_DESC_F_NEXT);

Regards, Bin