linux-kernel - Re: [PATCH V3 17/19] virtio_ring: factor out split indirect detaching logic

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Message-ID: <20250701024441-mutt-send-email-mst@kernel.org>
Date: Tue, 1 Jul 2025 02:44:52 -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 V3 17/19] virtio_ring: factor out split indirect
 detaching logic

On Mon, Jun 16, 2025 at 04:25:15PM +0800, Jason Wang wrote:
> Factor out the split indirect descriptor detaching logic in order to
> make it be reused by the in order support.

allow it to be reused

> 
> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/virtio/virtio_ring.c | 63 ++++++++++++++++++++----------------
>  1 file changed, 35 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index e8e0d1204f52..259380797ec4 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -773,11 +773,42 @@ static bool virtqueue_kick_prepare_split(struct vring_virtqueue *vq)
>  	return needs_kick;
>  }
>  
> +static void detach_indirect_split(struct vring_virtqueue *vq,
> +				  unsigned int head)
> +{
> +	struct vring_desc_extra *extra = vq->split.desc_extra;
> +	struct vring_desc *indir_desc =
> +	       vq->split.desc_state[head].indir_desc;
> +	unsigned int j;
> +	u32 len, num;
> +
> +	/* Free the indirect table, if any, now that it's unmapped. */
> +	if (!indir_desc)
> +		return;
> +	len = vq->split.desc_extra[head].len;
> +
> +	BUG_ON(!(vq->split.desc_extra[head].flags &
> +			VRING_DESC_F_INDIRECT));
> +	BUG_ON(len == 0 || len % sizeof(struct vring_desc));
> +
> +	num = len / sizeof(struct vring_desc);
> +
> +	extra = (struct vring_desc_extra *)&indir_desc[num];
> +
> +	if (vq->use_dma_api) {
> +		for (j = 0; j < num; j++)
> +			vring_unmap_one_split(vq, &extra[j]);
> +	}
> +
> +	kfree(indir_desc);
> +	vq->split.desc_state[head].indir_desc = NULL;
> +}
> +
>  static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
>  			     void **ctx)
>  {
>  	struct vring_desc_extra *extra;
> -	unsigned int i, j;
> +	unsigned int i;
>  	__virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
>  
>  	/* Clear data ptr. */
> @@ -801,34 +832,10 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
>  	/* Plus final descriptor */
>  	vq->vq.num_free++;
>  
> -	if (vq->indirect) {
> -		struct vring_desc *indir_desc =
> -				vq->split.desc_state[head].indir_desc;
> -		u32 len, num;
> -
> -		/* Free the indirect table, if any, now that it's unmapped. */
> -		if (!indir_desc)
> -			return;
> -		len = vq->split.desc_extra[head].len;
> -
> -		BUG_ON(!(vq->split.desc_extra[head].flags &
> -				VRING_DESC_F_INDIRECT));
> -		BUG_ON(len == 0 || len % sizeof(struct vring_desc));
> -
> -		num = len / sizeof(struct vring_desc);
> -
> -		extra = (struct vring_desc_extra *)&indir_desc[num];
> -
> -		if (vq->use_dma_api) {
> -			for (j = 0; j < num; j++)
> -				vring_unmap_one_split(vq, &extra[j]);
> -		}
> -
> -		kfree(indir_desc);
> -		vq->split.desc_state[head].indir_desc = NULL;
> -	} else if (ctx) {
> +	if (vq->indirect)
> +		detach_indirect_split(vq, head);
> +	else if (ctx)
>  		*ctx = vq->split.desc_state[head].indir_desc;
> -	}
>  }
>  
>  static bool virtqueue_poll_split(const struct vring_virtqueue *vq,
> -- 
> 2.34.1