On Tue, 22 Mar 2022 14:02:47 +0800, Jason Wang <jasow...@redhat.com> wrote:
>
> 在 2022/3/14 下午5:34, 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 <xuanz...@linux.alibaba.com>
> > ---
> > drivers/virtio/virtio_ring.c | 67 ++++++++++++++++++++++++++++++++++++
> > include/linux/virtio.h | 3 ++
> > 2 files changed, 70 insertions(+)
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index fb0abf9a2f57..b1dde086a8a4 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -2528,6 +2528,73 @@ 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 cb 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.
> > + * -ENOMEM: create new vring fail. But vq can still work
> > + * -EBUSY: reset/re-enable vq fail. vq may cannot work
> > + * -ENOENT: not support resize
> > + * -E2BIG/-EINVAL: param num error
> > + */
> > +int virtqueue_resize(struct virtqueue *vq, u32 num,
> > + void (*recycle)(struct virtqueue *vq, void *buf))
> > +{
> > + struct virtio_device *vdev = vq->vdev;
> > + void *buf;
> > + int err;
> > +
> > + if (num > vq->num_max)
> > + return -E2BIG;
> > +
> > + if (!num)
> > + return -EINVAL;
> > +
> > + if (to_vvq(vq)->packed.vring.num == num)
> > + return 0;
>
>
> Any reason we need to check a packed specific attribute here?
This is a mistake. Sorry for this.
>
>
> > +
> > + if (!vq->vdev->config->reset_vq)
> > + return -ENOENT;
> > +
> > + if (!vq->vdev->config->enable_reset_vq)
> > + return -ENOENT;
> > +
> > + err = vq->vdev->config->reset_vq(vq);
> > + if (err) {
> > + if (err != -ENOENT)
> > + err = -EBUSY;
> > + return err;
> > + }
> > +
> > + while ((buf = virtqueue_detach_unused_buf(vq)) != NULL)
> > + recycle(vq, buf);
> > +
> > + if (virtio_has_feature(vdev, VIRTIO_F_RING_PACKED))
> > + err = virtqueue_resize_packed(vq, num);
> > + else
> > + err = virtqueue_resize_split(vq, num);
> > +
> > + if (err)
> > + err = -ENOMEM;
>
>
> So this assumes that the -ENOMEM is the only possible error value for
> virtqueue_resize_xxx(). Is this true? (E.g wrong size)
Yes, I want the user to know at which step the error is returned.
>
>
> > +
> > + if (vq->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));
>
>
> I wonder what's the advantages of coupling virtqueue_reset in
> virtqueue_resize().
This is Michael's comment on the previous version
>
> It looks to me it wold be more flexible to let the driver do:
>
> rest()
>
> detach()
>
> resize()
>
> enable_reset()
>
> One reason is that in the future we may want to add more functionality
> e.g switching PASID during virtqueue reset.
Michael, from Jason Wang's plan, should we go back to the original 4 api model?
Thanks.
>
> Thanks
>
>
> > +
> > /**
> > * virtio_device - representation of a device using virtio
> > * @index: unique position on the virtio bus
>
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