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From:   Cindy Lu <lulu@redhat.com>
To:     lulu@redhat.com, jasowang@redhat.com, mst@redhat.com,
        xieyongji@bytedance.com, linux-kernel@vger.kernel.org,
        maxime.coquelin@redhat.com
Subject: [PATCH v3 7/7] Documentation: Add reconnect process for VDUSE
Date:   Tue,  5 Dec 2023 16:34:44 +0800
Message-Id: <20231205083444.3029239-8-lulu@redhat.com>
In-Reply-To: <20231205083444.3029239-1-lulu@redhat.com>
References: <20231205083444.3029239-1-lulu@redhat.com>
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Add a document explaining the reconnect process, including what the
Userspace App needs to do and how it works with the kernel.

Signed-off-by: Cindy Lu <lulu@redhat.com>
---
 Documentation/userspace-api/vduse.rst | 30 +++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/Documentation/userspace-api/vduse.rst b/Documentation/userspace-api/vduse.rst
index bdb880e01132..ec66e573f6da 100644
--- a/Documentation/userspace-api/vduse.rst
+++ b/Documentation/userspace-api/vduse.rst
@@ -231,3 +231,33 @@ 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 it does not exist, need to create the instance.
+   If it does exist, it means this is a reconnect and the program proceeds to step 3.
+
+1. Create a new VDUSE instance with ioctl(VDUSE_CREATE_DEV) on
+   /dev/vduse/control.
+
+2. When the ioctl(VDUSE_CREATE_DEV) function is called, the kernel allocates memory
+   to synchronize the reconnect information.
+
+3. Userspace App need to mmap the pages to userspace
+
+   When connecting for the first time, the userspace app must save the reconnect
+   information (struct vhost_reconnect_data) in mapped pages
+
+   If this is reconnect,If the purpose is to reconnect, the userspace application
+   must verify if the saved information is suitable for reconnection. Additionally,
+   the userspace application is required to set the "reconnected" bit in the
+   "struct vhost_reconnect_data" to "VDUSE_RECONNECT". The kernel will use this bit
+   to identify if the userspace application is reconnect.
+
+4. Start the userspace App.
+   userspace APP will call ioctl VDUSE_VQ_GET_INFO to sync the vq information.
+   Additionally, the APP must save the vq reconnect information (struct vdpa_vq_state)
+   in mapped pages while running.
+
+5. When the Userspace App exits, it is necessary to unmap all the reconnect pages.
-- 
2.34.3