xfree86: add a hook to replace the new console handler.

This hook is only necessary for the keyboard driver to remove the race
condition between drain_console() and the driver's ReadInput (Bug 29969).

The idea is that a driver that needs to handle events from the console
calls xf86ReplaceConsoleHandler() with it's own ReadInput (or NULL) and thus
removes the drain_console call. It's the driver's responsibility to restore
the previous behaviour when the driver is unloaded.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
CC: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Tiago Vignatti <tiago.vignatti@nokia.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>

hw/xfree86/common/xf86.h

@@ -203,6 +203,7 @@ extern _X_EXPORT pointer xf86AddGeneralHandler(int fd, InputHandlerProc proc, po
 extern _X_EXPORT int xf86RemoveGeneralHandler(pointer handler);
 extern _X_EXPORT void xf86DisableGeneralHandler(pointer handler);
 extern _X_EXPORT void xf86EnableGeneralHandler(pointer handler);
+extern _X_EXPORT InputHandlerProc xf86SetConsoleHandler(InputHandlerProc handler, pointer data);
 extern _X_EXPORT void xf86InterceptSignals(int *signo);
 extern _X_EXPORT void xf86InterceptSigIll(void (*sigillhandler)(void));
 extern _X_EXPORT Bool xf86EnableVTSwitch(Bool new);

hw/xfree86/common/xf86Events.c

@@ -600,6 +600,26 @@ xf86AddGeneralHandler(int fd, InputHandlerProc proc, pointer data)
     return ih;
 }
 
+/**
+ * Set the handler for the console's fd. Replaces (and returns) the previous
+ * handler or NULL, whichever appropriate.
+ * proc may be NULL if the server should not handle events on the console.
+ */
+InputHandlerProc
+xf86SetConsoleHandler(InputHandlerProc proc, pointer data)
+{
+    static InputHandlerProc handler = NULL;
+    InputHandlerProc old_handler = handler;
+
+    if (old_handler)
+        xf86RemoveGeneralHandler(old_handler);
+
+    xf86AddGeneralHandler(xf86Info.consoleFd, proc, data);
+    handler = proc;
+
+    return old_handler;
+}
+
 static void
 removeInputHandler(IHPtr ih)
 {

hw/xfree86/os-support/linux/lnx_init.c

@@ -277,9 +277,7 @@ xf86OpenConsole(void)
             tcsetattr(xf86Info.consoleFd, TCSANOW, &nTty);
 
             /* need to keep the buffer clean, else the kernel gets angry */
-	    if (xf86Info.allowEmptyInput)
+	    xf86SetConsoleHandler(drain_console, NULL);
-		console_handler = xf86AddGeneralHandler(xf86Info.consoleFd,
-							drain_console, NULL);
 
 	    /* we really should have a InitOSInputDevices() function instead
 	     * of Init?$#*&Device(). So I just place it here */