Add the document to explained how the reconnect process
include how the Userspace App need to do and how it works
with kernel

Signed-off-by: Cindy Lu <lulu@redhat.com>
---
 Documentation/userspace-api/vduse.rst | 29 +++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/Documentation/userspace-api/vduse.rst b/Documentation/userspace-api/vduse.rst
index bdb880e01132..6e01c21d94df 100644
--- a/Documentation/userspace-api/vduse.rst
+++ b/Documentation/userspace-api/vduse.rst
@@ -231,3 +231,32 @@ able to start the dataplane processing as follows:
    after the used ring is filled.
 
 For more details on the uAPI, please see include/uapi/linux/vduse.h.
+
+HOW VDUSE devices reconnectoin works
+----------------
+0. Userspace APP checks if the device /dev/vduse/vduse_name exists, if not create
+   the device. If yes means this is reconnect, goto 3
+
+1. Create a new VDUSE instance with ioctl(VDUSE_CREATE_DEV) on
+   /dev/vduse/control.
+
+2. In ioctl(VDUSE_CREATE_DEV), the kernel alloc the memory to sync the reconnect
+   information.
+
+3. Userspace App will mmap the pages to userspace
+
+   If this first time to connect, userspace App need save the reconnect
+   information (struct vhost_reconnect_data) in mapped pages
+
+   If this is reconnect, userspace App need to check if the saved information
+   OK to reconnect, Also userspace App MUST set the bit reconnected in
+   struct vhost_reconnect_data to 1. (kernel will use this bit to identify if the
+   userAPP is reconnected )
+
+4. Successfully start the userspace App.
+   userspace APP need to call ioctl VDUSE_VQ_GET_INFO to sync the vq information. also
+   APP need to save the reconnect information (struct vhost_reconnect_vring)
+   while running
+
+5. When the Userspace App exit, Userspace App need to unmap all the reconnect
+   pages
-- 
2.34.3