Re: [PATCH v9 18/32] virtio_ring: introduce virtqueue_resize()

[Jason Wang <jasowang@redhat.com>]

在 2022/4/6 上午11:43, Xuan Zhuo 写道:
> Introduce virtqueue_resize() to implement the resize of vring.
> Based on these, the driver can dynamically adjust the size of the vring.
> For example: ethtool -G.
>
> virtqueue_resize() implements resize based on the vq reset function. In
> case of failure to allocate a new vring, it will give up resize and use
> the original vring.
>
> During this process, if the re-enable reset vq fails, the vq can no
> longer be used. Although the probability of this situation is not high.
>
> The parameter recycle is used to recycle the buffer that is no longer
> used.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
>   drivers/virtio/virtio_ring.c | 69 ++++++++++++++++++++++++++++++++++++
>   include/linux/virtio.h       |  3 ++
>   2 files changed, 72 insertions(+)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 06f66b15c86c..6250e19fc5bf 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -2554,6 +2554,75 @@ struct virtqueue *vring_create_virtqueue(
>   }
>   EXPORT_SYMBOL_GPL(vring_create_virtqueue);
>   
> +/**
> + * virtqueue_resize - resize the vring of vq
> + * @_vq: the struct virtqueue we're talking about.
> + * @num: new ring num
> + * @recycle: callback for recycle the useless buffer
> + *
> + * When it is really necessary to create a new vring, it will set the current vq
> + * into the reset state. Then call the passed callback to recycle the buffer
> + * that is no longer used. Only after the new vring is successfully created, the
> + * old vring will be released.
> + *
> + * Caller must ensure we don't call this with other virtqueue operations
> + * at the same time (except where noted).
> + *
> + * Returns zero or a negative error.


Should we document that the virtqueue is kept unchanged (still 
available) on (specific) failure?


> + */
> +int virtqueue_resize(struct virtqueue *_vq, u32 num,
> +		     void (*recycle)(struct virtqueue *vq, void *buf))
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	struct virtio_device *vdev = vq->vq.vdev;
> +	bool packed;
> +	void *buf;
> +	int err;
> +
> +	if (!vq->we_own_ring)
> +		return -EINVAL;
> +
> +	if (num > vq->vq.num_max)
> +		return -E2BIG;
> +
> +	if (!num)
> +		return -EINVAL;
> +
> +	packed = virtio_has_feature(vdev, VIRTIO_F_RING_PACKED) ? true : false;
> +
> +	if ((packed ? vq->packed.vring.num : vq->split.vring.num) == num)
> +		return 0;
> +
> +	if (!vdev->config->reset_vq)
> +		return -ENOENT;
> +
> +	if (!vdev->config->enable_reset_vq)
> +		return -ENOENT;
> +
> +	err = vdev->config->reset_vq(_vq);
> +	if (err)
> +		return err;
> +
> +	while ((buf = virtqueue_detach_unused_buf(_vq)) != NULL)
> +		recycle(_vq, buf);
> +
> +	if (packed) {
> +		err = virtqueue_resize_packed(_vq, num);
> +		if (err)
> +			virtqueue_reinit_packed(vq);


Calling reinit here seems a little bit odd, it looks more like a reset 
of the virtqueue. Consider we may re-use virtqueue reset for more 
purpose, I wonder if we need a helper like:

virtqueue_resize() {
     vdev->config->reset_vq(_vq);
     if (packed)
         virtqueue_reinit_packed(_vq)
     else
         virtqueue_reinit_split(_vq)
}

Thanks


> +	} else {
> +		err = virtqueue_resize_split(_vq, num);
> +		if (err)
> +			virtqueue_reinit_split(vq);
> +	}
> +
> +	if (vdev->config->enable_reset_vq(_vq))
> +		return -EBUSY;
> +
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_resize);
> +
>   /* Only available for split ring */
>   struct virtqueue *vring_new_virtqueue(unsigned int index,
>   				      unsigned int num,
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index d59adc4be068..c86ff02e0ca0 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -91,6 +91,9 @@ dma_addr_t virtqueue_get_desc_addr(struct virtqueue *vq);
>   dma_addr_t virtqueue_get_avail_addr(struct virtqueue *vq);
>   dma_addr_t virtqueue_get_used_addr(struct virtqueue *vq);
>   
> +int virtqueue_resize(struct virtqueue *vq, u32 num,
> +		     void (*recycle)(struct virtqueue *vq, void *buf));
> +
>   /**
>    * virtio_device - representation of a device using virtio
>    * @index: unique position on the virtio bus