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@xxxxxxxxxx> --- Documentation/userspace-api/vduse.rst | 41 +++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) diff --git a/Documentation/userspace-api/vduse.rst b/Documentation/userspace-api/vduse.rst index bdb880e01132..7faa83462e78 100644 --- a/Documentation/userspace-api/vduse.rst +++ b/Documentation/userspace-api/vduse.rst @@ -231,3 +231,44 @@ 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 reconnection works +------------------------------------ +1. What is reconnection? + + When the userspace application loads, it should establish a connection + to the vduse kernel device. Sometimes,the userspace application exists, + and we want to support its restart and connect to the kernel device again + +2. How can I support reconnection in a userspace application? + +2.1 During initialization, the userspace application should first verify the + existence of the device "/dev/vduse/vduse_name". + If it doesn't exist, it means this is the first-time for connection. goto step 2.2 + If it exists, it means this is a reconnection, and we should goto step 2.3 + +2.2 Create a new VDUSE instance with ioctl(VDUSE_CREATE_DEV) on + /dev/vduse/control. + When ioctl(VDUSE_CREATE_DEV) is called, kernel allocates memory for + the reconnect information. The total memory size is PAGE_SIZE*vq_mumber. + +2.3 Check if the information is suitable for reconnect + If this is reconnection : + Before attempting to reconnect, The userspace application needs to use the + ioctl(VDUSE_DEV_GET_CONFIG, VDUSE_DEV_GET_STATUS, VDUSE_DEV_GET_FEATURES...) + to get the information from kernel. + Please review the information and confirm if it is suitable to reconnect. + +2.4 Userspace application needs to mmap the memory to userspace + The userspace application requires mapping one page for every vq. These pages + should be used to save vq-related information during system running. Additionally, + the application must define its own structure to store information for reconnection. + +2.5 Completed the initialization and running the application. + While the application is running, it is important to store relevant information + about reconnections in mapped pages. When calling the ioctl VDUSE_VQ_GET_INFO to + get vq information, it's necessary to check whether it's a reconnection. If it is + a reconnection, the vq-related information must be get from the mapped pages. + +2.6 When the Userspace application exits, it is necessary to unmap all the + pages for reconnection -- 2.43.0