Re: [RFC v3 5/7] virtio: unmask F_NEXT flag in desc_extra

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

On Thu,  1 Sep 2022 13:54:32 +0800, Guo Zhi <qtxuning1999@sjtu.edu.cn> wrote:
> We didn't unmask F_NEXT flag in desc_extra in the end of a chain,
> unmask it so that we can access desc_extra to get next information.
>
> Signed-off-by: Guo Zhi <qtxuning1999@sjtu.edu.cn>
> ---
>  drivers/virtio/virtio_ring.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index a5ec724c01d8..00aa4b7a49c2 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -567,7 +567,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>  	}
>  	/* Last one doesn't continue. */
>  	desc[prev].flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT);
> -	if (!indirect && vq->use_dma_api)
> +	if (!indirect)
>  		vq->split.desc_extra[prev & (vq->split.vring.num - 1)].flags &=
>  			~VRING_DESC_F_NEXT;
>
> @@ -584,6 +584,8 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>  					 total_sg * sizeof(struct vring_desc),
>  					 VRING_DESC_F_INDIRECT,
>  					 false);
> +		vq->split.desc_extra[head & (vq->split.vring.num - 1)].flags &=
> +			~VRING_DESC_F_NEXT;

Wondering if this is necessary? When setting flags, NEXT is not included.

>  	}
>
>  	/* We're using some buffers from the free list. */
> @@ -685,7 +687,6 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
>  			     void **ctx)
>  {
>  	unsigned int i, j;
> -	__virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
>
>  	/* Clear data ptr. */
>  	vq->split.desc_state[head].data = NULL;
> @@ -693,7 +694,7 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
>  	/* Put back on free list: unmap first-level descriptors and find end */
>  	i = head;
>
> -	while (vq->split.vring.desc[i].flags & nextflag) {
> +	while (vq->split.desc_extra[i].flags & VRING_DESC_F_NEXT) {
>  		vring_unmap_one_split(vq, i);
>  		i = vq->split.desc_extra[i].next;
>  		vq->vq.num_free++;
> --
> 2.17.1
>