linux-kernel - Re: [PATCH V8 18/19] virtio_ring: factor out split detaching logic

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Message-ID: <20251020111413-mutt-send-email-mst@kernel.org>
Date: Mon, 20 Oct 2025 11:18:09 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: xuanzhuo@...ux.alibaba.com, eperezma@...hat.com,
	virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V8 18/19] virtio_ring: factor out split detaching logic

On Mon, Oct 20, 2025 at 03:10:02PM +0800, Jason Wang wrote:
> This patch factors out the split core detaching logic that could be
> reused by in order feature into a dedicated function.
> 
> Acked-by: Eugenio Pérez <eperezma@...hat.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/virtio/virtio_ring.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 0f07a6637acb..96d7f165ec88 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -802,8 +802,9 @@ static void detach_indirect_split(struct vring_virtqueue *vq,
>  	vq->split.desc_state[head].indir_desc = NULL;
>  }
>  
> -static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
> -			     void **ctx)
> +static unsigned detach_buf_split_in_order(struct vring_virtqueue *vq,
> +					  unsigned int head,
> +					  void **ctx)


Well not really _inorder, right? This is a common function.
You want to call it __detach_buf_split or something maybe.

Additionally the very first line in there is:

        __virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);

and the byte swap is not needed for inorder.
you could just do __cpu_to_virtio16(true, VRING_DESC_F_NEXT)




>  {
>  	struct vring_desc_extra *extra;
>  	unsigned int i;
> @@ -824,8 +825,6 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
>  	}
>  
>  	vring_unmap_one_split(vq, &extra[i]);
> -	vq->split.desc_extra[i].next = vq->free_head;
> -	vq->free_head = head;
>  
>  	/* Plus final descriptor */
>  	vq->vq.num_free++;
> @@ -834,6 +833,17 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
>  		detach_indirect_split(vq, head);
>  	else if (ctx)
>  		*ctx = vq->split.desc_state[head].indir_desc;
> +
> +	return i;
> +}
> +
> +static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
> +			     void **ctx)
> +{
> +	unsigned int i = detach_buf_split_in_order(vq, head, ctx);
> +
> +	vq->split.desc_extra[i].next = vq->free_head;
> +	vq->free_head = head;
>  }
>  
>  static bool virtqueue_poll_split(const struct vring_virtqueue *vq,
> -- 
> 2.31.1