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

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

On Tue, 12 Apr 2022 14:41:18 +0800, Jason Wang <jasowang@redhat.com> wrote:
>
> 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


I also feel that this is a bit odd, I will put virtqueue_reinit_* into
virtqueue_resize_*.

Thanks.

> 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
>