[PATCH v11 08/40] virtio_ring: split: extract the logic of alloc queue

[Xuan Zhuo]

On Mon, 4 Jul 2022 11:59:03 +0800, Jason Wang <jasowang at redhat.com> wrote:
>
> 在 2022/7/1 16:45, Xuan Zhuo 写道:
> > On Fri, 1 Jul 2022 16:26:25 +0800, Jason Wang <jasowang at redhat.com> wrote:
> >> 在 2022/6/29 14:56, 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 49d61e412dc6..a9ceb9c16c54 100644
> >>> --- a/drivers/virtio/virtio_ring.c
> >>> +++ b/drivers/virtio/virtio_ring.c
> >>> @@ -949,28 +949,19 @@ static void vring_free_split(struct vring_virtqueue_split *vring,
> >>>    	kfree(vring->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,
> >>> +				   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 */
> >>> @@ -981,11 +972,11 @@ 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! */
> >>> @@ -993,21 +984,46 @@ static struct virtqueue *vring_create_virtqueue_split(
> >>>    					  &dma_addr, GFP_KERNEL|__GFP_ZERO);
> >>>    	}
> >>>    	if (!queue)
> >>> -		return NULL;
> >>> +		return -ENOMEM;
> >>> +
> >>> +	vring_init(&vring->vring, num, queue, vring_align);
> >>>
> >>> -	queue_size_in_bytes = vring_size(num, vring_align);
> >>> -	vring_init(&vring, num, queue, vring_align);
> >>> +	vring->queue_dma_addr = dma_addr;
> >>> +	vring->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 = {};
> >>> +	struct virtqueue *vq;
> >>> +	int err;
> >>> +
> >>> +	err = vring_alloc_queue_split(&vring, 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.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, 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.queue_dma_addr;
> >>
> >> Nit: having two queue_dma_addr seems redundant (so did queue_size_in_bytes).
> > two?
> >
> > Where is the problem I don't understand?
> >
> > Thanks.
>
>
> I meant we had:
>
>          vring.vring = _vring;
>
> in __vring_new_virtqueue().
>
> This means we'd better initialize vring fully before that?
>
> E.g
>
> vring.queue_dma_addr = dma_addr;
>
> ...
>
> __vring_new_virtqueue()

oh, my bad, maybe the repeated use of the name "vring" led to a
misunderstanding.

What is passed to __vring_new_virtqueue is the structure struct vring

struct vring {
	unsigned int num;

	vring_desc_t *desc;

	vring_avail_t *avail;

	vring_used_t *used;
};

And what contains queue_dma_addr is our newly split structure struct
vring_virtqueue_split

struct vring_virtqueue_split {
	/* Actual memory layout for this queue. */
	struct vring vring;

	/* Last written value to avail->flags */
	u16 avail_flags_shadow;

	/*
	 * Last written value to avail->idx in
	 * guest byte order.
	 */
	u16 avail_idx_shadow;

	/* Per-descriptor state. */
	struct vring_desc_state_split *desc_state;
	struct vring_desc_extra *desc_extra;

	/* DMA address and size information */
	dma_addr_t queue_dma_addr;
	size_t queue_size_in_bytes;

	/*
	 * The parameters for creating vrings are reserved for creating new
	 * vring.
	 */
	u32 vring_align;
	bool may_reduce_num;
};

We have no way to pass queue_dma_addr into __vring_new_virtqueue. But for the
uniformity of the interface, I create a temporary struct vring_virtqueue_split
vring_split(your suggestion) in __vring_new_virtqueue. Then assign the passed
in struct vring to it

	vring.vring = _vring.

So here vring is an empty temporary variable.

As you have replied in other patches, my re-use of the name vring is a mistake,
I will change some places to vring_split and vring_packed.

Thanks.


>
> Thanks
>
>
> >
> >> Thanks
> >>
> >>
> >>> +	to_vvq(vq)->split.queue_size_in_bytes = vring.queue_size_in_bytes;
> >>>    	to_vvq(vq)->we_own_ring = true;
> >>>
> >>>    	return vq;
>