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(reset_vq,
enable_reset_vq) in struct virtio_config_ops to implement steps 1 and 4.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
 include/linux/virtio_config.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index b47c2e7ed0ee..ded51b0d4823 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h

@@ -78,6 +78,16 @@ 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 (optional).
+ *     vq: the virtqueue
+ *     Returns 0 on success or error status
+ *     reset_vq 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_reset_vq: enable a reset queue
+ *     vq: the virtqueue
+ *     Returns 0 on success or error status
+ *     If reset_vq is set, then enable_reset_vq must also be set.
  */
 typedef void vq_callback_t(struct virtqueue *);
 struct virtio_config_ops {

@@ -104,6 +114,8 @@ 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);