On Fri, Mar 29, 2024 at 05:38:25PM +0800, Cindy Lu wrote: > 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..f903aed714d1 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 reconnectoin works typo > +------------------------------------ > +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. > + I don't get it. So this is just a way for the application to allocate memory? Why do we need this new way to do it? Why not just mmap a file anywhere at all? > +2.6 When the Userspace application exits, it is necessary to unmap all the > + pages for reconnection > -- > 2.43.0
