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

[Mario <ml@kernelobjects.org>]

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