[PATCH v2] Documentation: Add reconnect process for VDUSE

[PATCH v2] Documentation: Add reconnect process for VDUSE

[Cindy Lu]

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..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
+------------------------------------
+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

Re: [PATCH v2] Documentation: Add reconnect process for VDUSE

[Michael S. Tsirkin]

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@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..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

Re: [PATCH v2] Documentation: Add reconnect process for VDUSE

[Cindy Lu]

On Fri, Mar 29, 2024 at 5:52 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> 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@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..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
>
Really sorry for this, I will send a new version

Thanks
Cindy
> > +------------------------------------
> > +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?
>
We used to use tmpfs to save this reconnect information,
but this will make the API not self contained, so we changed to using
the kernel memory
Thanks
cindy



>
> > +2.6 When the Userspace application exits, it is necessary to unmap all the
> > +    pages for reconnection
> > --
> > 2.43.0
>