virtio: struct virtio_config_ops add callbacks for queue_reset

reset can be divided into the following four steps (example):
 1. transport: notify the device to reset the queue
 2. vring:     recycle the buffer submitted
 3. vring:     reset/resize the vring (may re-alloc)
 4. transport: mmap vring to device, and enable the queue

In order to support queue reset, add two callbacks in struct
virtio_config_ops to implement steps 1 and 4.
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20220801063902.129329-3-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

include/linux/virtio_config.h

@@ -78,6 +78,18 @@ 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.
+ * @disable_vq_and_reset: reset a queue individually (optional).
+ *	vq: the virtqueue
+ *	Returns 0 on success or error status
+ *	disable_vq_and_reset will guarantee that the callbacks are disabled and
+ *	synchronized.
+ *	Except for the callback, the caller should guarantee that the vring is
+ *	not accessed by any functions of virtqueue.
+ * @enable_vq_after_reset: enable a reset queue
+ *	vq: the virtqueue
+ *	Returns 0 on success or error status
+ *	If disable_vq_and_reset is set, then enable_vq_after_reset must also be
+ *	set.
  */
 typedef void vq_callback_t(struct virtqueue *);
 struct virtio_config_ops {
@@ -104,6 +116,8 @@ struct virtio_config_ops {
 			int index);
 	bool (*get_shm_region)(struct virtio_device *vdev,
 			       struct virtio_shm_region *region, u8 id);
+	int (*disable_vq_and_reset)(struct virtqueue *vq);
+	int (*enable_vq_after_reset)(struct virtqueue *vq);
 };
 
 /* If driver didn't advertise the feature, it will never appear. */