Changes to XInput Proto Number of Events Cause Xlib WireToEvent Vector Mismatch

[Julien Cristau]

On Thu, Nov 26, 2009 at 11:45:39 +1000, Peter Hutterer wrote:

> @@ -117,10 +118,51 @@ XExtDisplayInfo *XextAddDisplay (
>       */
>      if (dpyinfo->codes) {
>  	int i, j;
> +	int idx = dpyinfo->codes->first_event & 0x3f;
> +
> +
> +	/* Xlib extensions use compiled in event numbers. A new library
> +	 * against an older server may thus expect a different (higher)
> +	 * number of events than the server will send. We have no way of
> +	 * knowing the number of events for an extension, the server won't
> +	 * tell us.
> +	 *
> +	 * Depending on the extension initialization order, this smashes the
> +	 * event_vec[type] for anything after the extension with the
> +	 * different number of events.
> +	 *
> +	 * e.g. server with inputproto 1.3 expects 15 events, libXi with
> +	 * inputproto 2.0 expects 17 events.
> +	 * base code is 80, events [80,96] are handled by libXi. events [95,
> +	 * 96] belong to the next extension already though.
> +	 * This requires XI to be initialized after the extension occupying
> +	 * the next range of event codes.
> +	 *
> +	 * To avoid this, we have a zeroed out array of extension handlers.
> +	 * If an extension handler for an event type is already set, and the
> +	 * previous event code (before base_code) is the same extension, we
> +	 * have the nevents conflict. Unset all those handlers and allow
> +	 * overwriting them with the new handlers.
> +         *
> +         * If a handler for a (base + n) event is already set, stop
> +         * registering this extension for the event codes.

there's some whitespace issues here...

> +	 *
> +	 * event_codes are subtracted by 64 since we don't need to worry
> +	 * about core.
> +	 */
> +
> +	if (idx && ext_handlers[idx - 1] == ext_handlers[idx]) {
> +	    for (i = idx; i < idx + nevents; i++)
> +		if (ext_handlers[idx - 1] == ext_handlers[i])
> +		    ext_handlers[i] = 0;
> +	}

Shouldn't this loop actually look like:

for (i = idx; i < 64; i++)
    if (ext_handlers[idx - 1] == ext_handlers[i])
        ext_handlers[i] = 0;
    else
        break;

Otherwise if extension1 registers events base to base+10, then
extension2 comes and registers events base+5 to base+7, there'll still
be some wrong values for base+8 to base+10, and extension3 will leave
them alone.

>  
> -	for (i = 0, j = dpyinfo->codes->first_event; i < nevents; i++, j++) {
> +	for (i = 0, j = dpyinfo->codes->first_event; i < nevents; i++, j++, idx++) {
> +	    if (ext_handlers[idx]) /* don't smash the following extension */
> +		break;
>  	    XESetWireToEvent (dpy, j, hooks->wire_to_event);
>  	    XESetEventToWire (dpy, j, hooks->event_to_wire);
> +	    ext_handlers[idx] = dpyinfo->codes->first_event & 0x3f;
>  	}
>  
>          /* register extension for XGE */

Cheers,
Julien