Re: [PATCH v3] Documentation: Add reconnect process for VDUSE

From: Michael S. Tsirkin
Date: Mon Apr 08 2024 - 03:40:11 EST


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@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.

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