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

[Xuan Zhuo]

On Thu, 21 Jul 2022 17:13:49 +0800, Jason Wang <jasowang at redhat.com> wrote:
>
> 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 at linux.alibaba.com>
> > ---
> >   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;

This does look simpler. The reason for not doing this is that the argument
accepted by __vring_new_virtqueue() is "struct vring", and
__vring_new_virtqueue() is an export symbol.

I took a look, and the only external direct call to __vring_new_virtqueue is
here.

	tools/virtio/virtio_test.c
	static void vq_reset(struct vq_info *info, int num, struct virtio_device *vdev)
	{
		if (info->vq)
			vring_del_virtqueue(info->vq);

		memset(info->ring, 0, vring_size(num, 4096));
		vring_init(&info->vring, num, info->ring, 4096);
		info->vq = __vring_new_virtqueue(info->idx, info->vring, vdev, true,
						 false, vq_notify, vq_callback, "test");
		assert(info->vq);
		info->vq->priv = info;
	}

I think this could be replaced with vring_new_virtqueue() so that we don't need
to make __vring_new_virtqueue as an export function so we can make some
modifications to it.

nit: vring_alloc_desc_extra() should not have to be extract from
__vring_new_virtqueue() .

Thanks.

>
> And if this makes sense, we can do something similar to packed ring.
>
> Thanks
>
>
> >   	to_vvq(vq)->we_own_ring = true;
> >
> >   	return vq;
>