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    SubjectRe: [PATCH v3] Documentation: Add reconnect process for VDUSE
    On Thu, Apr 04, 2024 at 01:56:31PM +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@redhat.com>
    > ---
    > 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.

    Confused. Where is that allocation, in code?

    Thanks!

    > +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


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