[Qemu-devel] Request for comment - dynamic VNC keyboard mapping

[Mario]

Hi all,

I have a question related to the VNC server keyboard settings. Currently the 
user of qemu has to decide before VM startup which language is used for VNC 
keyboard mapping. If no keyboard is configured, the en-us keyboard will be 
loaded for keysym to scancode conversion. A later reconfiguration of the 
keyboard is not possible at present.

So here is my idea:

The VNC Display context stores a list of loaded keyboards (like vs->vd->kbds). 
If no keyboard was specified, at least the default will be added to the list 
("en-us"?). If a client connects, a copy of the (latest configured) pointer 
will be stored within the VncState structure. For any keys sent by this client 
the own keyboard reference will be used.

As (in theory) every VNC client may have a differen keyboard layout, in my 
point of view it makes sense to attach the keyboard used for keysym2scancode() 
to the client context rather to the VNC server context. However as (most 
likely) all clients do have the same keyboard mapping it would be an overhead 
to parse and store the mapping list each time the client connects.

Now in my idea two mechanisms may change the behavior of the client keyboard.

1.) a qmp command was sent, that sets /configures for a particular/default 
keyboard.
2.) within the VNC protocol a 
"VNC_MSG_CLIENT_QEMU/VNC_MSG_CLIENT_QEMU_EXT_KEYBOARD_LAYOUT" message arrives

If the new keyboard was not already loaded and stored inside vs->vd->kbds , 
qemu initializes the new mapping. The affected VNC client (VncState) again 
stores the reference only.

This enables switching the keyboard layout during runtime as well as using 
multiple different keyboard layouts at atime.

Together with a corresponding patch I would also add a patch for libvncclient 
to have a reference implmentation for the integrated keyboard layout switching.

What are your thoughts about this kind of improvement?

Thanks,
Mario