Re: [PATCH v12 08/40] virtio_ring: split: extract the logic of alloc queue

[Jason Wang <jasowang@xxxxxxxxxx>]

在 2022/7/20 11:04, Xuan Zhuo 写道:
> Separate the logic of split to create vring queue.
>
> This feature is required for subsequent virtuqueue reset vring.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> ---
>   drivers/virtio/virtio_ring.c | 68 ++++++++++++++++++++++--------------
>   1 file changed, 42 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index c94c5461e702..c7971438bb2c 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -950,28 +950,19 @@ static void vring_free_split(struct vring_virtqueue_split *vring_split,
>   	kfree(vring_split->desc_extra);
>   }
>   
> -static struct virtqueue *vring_create_virtqueue_split(
> -	unsigned int index,
> -	unsigned int num,
> -	unsigned int vring_align,
> -	struct virtio_device *vdev,
> -	bool weak_barriers,
> -	bool may_reduce_num,
> -	bool context,
> -	bool (*notify)(struct virtqueue *),
> -	void (*callback)(struct virtqueue *),
> -	const char *name)
> +static int vring_alloc_queue_split(struct vring_virtqueue_split *vring_split,
> +				   struct virtio_device *vdev,
> +				   u32 num,
> +				   unsigned int vring_align,
> +				   bool may_reduce_num)
>   {
> -	struct virtqueue *vq;
>   	void *queue = NULL;
>   	dma_addr_t dma_addr;
> -	size_t queue_size_in_bytes;
> -	struct vring vring;
>   
>   	/* We assume num is a power of 2. */
>   	if (num & (num - 1)) {
>   		dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
> -		return NULL;
> +		return -EINVAL;
>   	}
>   
>   	/* TODO: allocate each queue chunk individually */
> @@ -982,11 +973,11 @@ static struct virtqueue *vring_create_virtqueue_split(
>   		if (queue)
>   			break;
>   		if (!may_reduce_num)
> -			return NULL;
> +			return -ENOMEM;
>   	}
>   
>   	if (!num)
> -		return NULL;
> +		return -ENOMEM;
>   
>   	if (!queue) {
>   		/* Try to get a single page. You are my only hope! */
> @@ -994,21 +985,46 @@ static struct virtqueue *vring_create_virtqueue_split(
>   					  &dma_addr, GFP_KERNEL|__GFP_ZERO);
>   	}
>   	if (!queue)
> -		return NULL;
> +		return -ENOMEM;
> +
> +	vring_init(&vring_split->vring, num, queue, vring_align);
>   
> -	queue_size_in_bytes = vring_size(num, vring_align);
> -	vring_init(&vring, num, queue, vring_align);
> +	vring_split->queue_dma_addr = dma_addr;
> +	vring_split->queue_size_in_bytes = vring_size(num, vring_align);
> +
> +	return 0;
> +}
> +
> +static struct virtqueue *vring_create_virtqueue_split(
> +	unsigned int index,
> +	unsigned int num,
> +	unsigned int vring_align,
> +	struct virtio_device *vdev,
> +	bool weak_barriers,
> +	bool may_reduce_num,
> +	bool context,
> +	bool (*notify)(struct virtqueue *),
> +	void (*callback)(struct virtqueue *),
> +	const char *name)
> +{
> +	struct vring_virtqueue_split vring_split = {};
> +	struct virtqueue *vq;
> +	int err;
> +
> +	err = vring_alloc_queue_split(&vring_split, vdev, num, vring_align,
> +				      may_reduce_num);
> +	if (err)
> +		return NULL;
>   
> -	vq = __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
> -				   notify, callback, name);
> +	vq = __vring_new_virtqueue(index, vring_split.vring, vdev, weak_barriers,
> +				   context, notify, callback, name);
>   	if (!vq) {
> -		vring_free_queue(vdev, queue_size_in_bytes, queue,
> -				 dma_addr);
> +		vring_free_split(&vring_split, vdev);
>   		return NULL;
>   	}
>   
> -	to_vvq(vq)->split.queue_dma_addr = dma_addr;
> -	to_vvq(vq)->split.queue_size_in_bytes = queue_size_in_bytes;
> +	to_vvq(vq)->split.queue_dma_addr = vring_split.queue_dma_addr;
> +	to_vvq(vq)->split.queue_size_in_bytes = vring_split.queue_size_in_bytes;


This still seems a little bit redundant since the current logic is a 
little bit complicated since the vq->split is not initialized in a 
single place.

I wonder if it's better to:

vring_alloc_queue_split()
vring_alloc_desc_extra() (reorder to make patch 9 come first)

then we can simply assign vring_split to vq->split in 
__vring_new_virtqueue() since it has:

    vq->split.queue_dma_addr = 0;
    vq->split.queue_size_in_bytes = 0;

    vq->split.vring = vring;
    vq->split.avail_flags_shadow = 0;
    vq->split.avail_idx_shadow = 0;

This seems to simplify the logic and task of e.g 
virtqueue_vring_attach_split() to a simple:

vq->split= vring_split;

And if this makes sense, we can do something similar to packed ring.

Thanks


>   	to_vvq(vq)->we_own_ring = true;
>   
>   	return vq;