Virtualization - Jul 2022 - [PATCH v13 16/42] virtio_ring: split: introduce virtqueue_resize_split()

virtio ring split supports resize.

Only after the new vring is successfully allocated based on the new num,
we will release the old vring. In any case, an error is returned,
indicating that the vring still points to the old vring.

In the case of an error, re-initialize(virtqueue_reinit_split()) the
virtqueue to ensure that the vring can be used.

Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
Acked-by: Jason Wang <jasowang at redhat.com>
---
 drivers/virtio/virtio_ring.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index b6fda91c8059..58355e1ac7d7 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -220,6 +220,7 @@ static struct virtqueue *__vring_new_virtqueue(unsigned int
index,
 					       void (*callback)(struct virtqueue *),
 					       const char *name);
 static struct vring_desc_extra *vring_alloc_desc_extra(unsigned int num);
+static void vring_free(struct virtqueue *_vq);
 
 /*
  * Helpers.
@@ -1117,6 +1118,39 @@ static struct virtqueue *vring_create_virtqueue_split(
 	return vq;
 }
 
+static int virtqueue_resize_split(struct virtqueue *_vq, u32 num)
+{
+	struct vring_virtqueue_split vring_split = {};
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	struct virtio_device *vdev = _vq->vdev;
+	int err;
+
+	err = vring_alloc_queue_split(&vring_split, vdev, num,
+				      vq->split.vring_align,
+				      vq->split.may_reduce_num);
+	if (err)
+		goto err;
+
+	err = vring_alloc_state_extra_split(&vring_split);
+	if (err) {
+		vring_free_split(&vring_split, vdev);
+		goto err;
+	}
+
+	vring_free(&vq->vq);
+
+	virtqueue_vring_init_split(&vring_split, vq);
+
+	virtqueue_init(vq, vring_split.vring.num);
+	virtqueue_vring_attach_split(vq, &vring_split);
+
+	return 0;
+
+err:
+	virtqueue_reinit_split(vq);
+	return -ENOMEM;
+}
+
 
 /*
  * Packed ring specific functions - *_packed().
-- 
2.31.0

? 2022/7/26 15:21, Xuan Zhuo ??:
> virtio ring split supports resize.
>
> Only after the new vring is successfully allocated based on the new num,
> we will release the old vring. In any case, an error is returned,
> indicating that the vring still points to the old vring.
>
> In the case of an error, re-initialize(virtqueue_reinit_split()) the
> virtqueue to ensure that the vring can be used.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
> Acked-by: Jason Wang <jasowang at redhat.com>
> ---
>   drivers/virtio/virtio_ring.c | 34 ++++++++++++++++++++++++++++++++++
>   1 file changed, 34 insertions(+)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index b6fda91c8059..58355e1ac7d7 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -220,6 +220,7 @@ static struct virtqueue *__vring_new_virtqueue(unsigned
int index,
>   					       void (*callback)(struct virtqueue *),
>   					       const char *name);
>   static struct vring_desc_extra *vring_alloc_desc_extra(unsigned int num);
> +static void vring_free(struct virtqueue *_vq);
>   
>   /*
>    * Helpers.
> @@ -1117,6 +1118,39 @@ static struct virtqueue
*vring_create_virtqueue_split(
>   	return vq;
>   }
>   
> +static int virtqueue_resize_split(struct virtqueue *_vq, u32 num)
> +{
> +	struct vring_virtqueue_split vring_split = {};
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	struct virtio_device *vdev = _vq->vdev;
> +	int err;
> +
> +	err = vring_alloc_queue_split(&vring_split, vdev, num,
> +				      vq->split.vring_align,
> +				      vq->split.may_reduce_num);
> +	if (err)
> +		goto err;

I think we don't need to do anything here?

> +
> +	err = vring_alloc_state_extra_split(&vring_split);
> +	if (err) {
> +		vring_free_split(&vring_split, vdev);
> +		goto err;

I suggest to move vring_free_split() into a dedicated error label.

Thanks

> +	}
> +
> +	vring_free(&vq->vq);
> +
> +	virtqueue_vring_init_split(&vring_split, vq);
> +
> +	virtqueue_init(vq, vring_split.vring.num);
> +	virtqueue_vring_attach_split(vq, &vring_split);
> +
> +	return 0;
> +
> +err:
> +	virtqueue_reinit_split(vq);
> +	return -ENOMEM;
> +}
> +
>   
>   /*
>    * Packed ring specific functions - *_packed().