Input hotplug issue : Handling the first key from new device

[Henry Zhao]

In a system with multiple input keyboard devices, mapping table switch 
takes place when server receives the first keystroke from a new device. 
At that time the server does the followig (in that sequence):

* updating mapping tables to the new device
* sending MappingNotify to clients
* Processing the key event

On receiving MappingNotify, a client usually does a new grab in 
accordance with the new mapping table. However, server creates a grab 
for it AFTER it processed the key event, therefore the key event is 
incorrectly delivered. In my testing case, the client grabs a keysym only 
defined in the new device. When the first key that happens to correspond 
to that keysym is hit from the new device, the client does a grab, but 
the grab is not there when server processes the event, so the client 
misses it (although the client is able to correctly catch subsequent keys 
from the new device).

I tried something, including deferring processing key event for several 
dispatch loops, or having driver send a dummy keycode (with an extra 
select) for mapping table updates only, but all in vein.

Is it an architectural issue ?  Any solutions ?


-Henry