Virtualization - Feb 2022 - [PATCH v4 09/14] virtio: queue_reset: struct virtio_config_ops add callbacks for queue_reset

Performing reset on a queue is divided into four steps:

1. reset_vq: reset one vq
2. recycle the buffer from vq by virtqueue_detach_unused_buf()
3. release the ring of the vq by vring_release_virtqueue()
4. enable_reset_vq: re-enable the reset queue

So add two callbacks reset_vq, enable_reset_vq to struct
virtio_config_ops.

Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
---
 include/linux/virtio_config.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 4d107ad31149..0d01a64f2576 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -74,6 +74,17 @@ struct virtio_shm_region {
  * @set_vq_affinity: set the affinity for a virtqueue (optional).
  * @get_vq_affinity: get the affinity for a virtqueue (optional).
  * @get_shm_region: get a shared memory region based on the index.
+ * @reset_vq: reset a queue individually
+ *	vq: the virtqueue
+ *	Returns 0 on success or error status
+ *	After successfully calling this, be sure to call
+ *	virtqueue_detach_unused_buf() to recycle the buffer in the ring, and
+ *	then call vring_release_virtqueue() to release the vq ring.
+ * @enable_reset_vq: enable a reset queue
+ *	vq: the virtqueue
+ *	ring_num: specify ring num for the vq to be re-enabled. 0 means use the
+ *	          default value. MUST be a power of 2.
+ *	Returns 0 on success or error status
  */
 typedef void vq_callback_t(struct virtqueue *);
 struct virtio_config_ops {
@@ -100,6 +111,8 @@ struct virtio_config_ops {
 			int index);
 	bool (*get_shm_region)(struct virtio_device *vdev,
 			       struct virtio_shm_region *region, u8 id);
+	int (*reset_vq)(struct virtqueue *vq);
+	int (*enable_reset_vq)(struct virtqueue *vq, u16 ring_num);
 };
 
 /* If driver didn't advertise the feature, it will never appear. */
-- 
2.31.0

? 2022/2/9 ??8:28, Xuan Zhuo ??:
> Performing reset on a queue is divided into four steps:
>
> 1. reset_vq: reset one vq
> 2. recycle the buffer from vq by virtqueue_detach_unused_buf()
> 3. release the ring of the vq by vring_release_virtqueue()
> 4. enable_reset_vq: re-enable the reset queue
>
> So add two callbacks reset_vq, enable_reset_vq to struct
> virtio_config_ops.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
> ---
>   include/linux/virtio_config.h | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
>
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index 4d107ad31149..0d01a64f2576 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -74,6 +74,17 @@ struct virtio_shm_region {
>    * @set_vq_affinity: set the affinity for a virtqueue (optional).
>    * @get_vq_affinity: get the affinity for a virtqueue (optional).
>    * @get_shm_region: get a shared memory region based on the index.
> + * @reset_vq: reset a queue individually

This needs to be marked as optional I think.

> + *	vq: the virtqueue
> + *	Returns 0 on success or error status

It looks to me the caller should also guarantee that the vring is not 
accsed by any functions e.g NAPI.

> + *	After successfully calling this, be sure to call
> + *	virtqueue_detach_unused_buf() to recycle the buffer in the ring, and
> + *	then call vring_release_virtqueue() to release the vq ring.
> + * @enable_reset_vq: enable a reset queue
> + *	vq: the virtqueue
> + *	ring_num: specify ring num for the vq to be re-enabled. 0 means use the
> + *	          default value. MUST be a power of 2.

Note that we don't have power of 2 requirement for packed virtqueue.

And I wonder if it's cleaner to have a find_vq() ops instead to dealing 
with the re-allocation and possible size change, or have a dedicated 
helper to set vring size so driver can do.

reset_vq()

virtqueue_set_vring_size()

enable_reset_vq()

> + *	Returns 0 on success or error status
>    */
>   typedef void vq_callback_t(struct virtqueue *);
>   struct virtio_config_ops {
> @@ -100,6 +111,8 @@ struct virtio_config_ops {
>   			int index);
>   	bool (*get_shm_region)(struct virtio_device *vdev,
>   			       struct virtio_shm_region *region, u8 id);
> +	int (*reset_vq)(struct virtqueue *vq);
> +	int (*enable_reset_vq)(struct virtqueue *vq, u16 ring_num);

Note that the current implement is best-effort, so it's not guarantee 
that we can have a vring with ring_num, we may get less under memory 
pressure or even fail. We probably need to have a pamater to mandate the 
ring_num otherwise user may surprise to see a decreased size of the ring 
when a increasing is actually requested.

Thanks

>   };
>   
>   /* If driver didn't advertise the feature, it will never appear. */