input-linux: add shift+shift as a grab toggle

We have ctrl-ctrl and alt-alt; why not shift-shift? That's my preferred
grab binding, personally.

Signed-off-by: Niklas Haas <git@haasn.xyz>
Message-id: 20190818105038.19520-1-qemu@haasn.xyz
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

qapi/ui.json

@@ -1025,7 +1025,8 @@
 #
 ##
 { 'enum': 'GrabToggleKeys',
-  'data': [ 'ctrl-ctrl', 'alt-alt', 'meta-meta', 'scrolllock', 'ctrl-scrolllock' ] }
+  'data': [ 'ctrl-ctrl', 'alt-alt', 'shift-shift','meta-meta', 'scrolllock',
+            'ctrl-scrolllock' ] }
 
 ##
 # @DisplayGTK:

ui/input-linux.c

@@ -113,6 +113,10 @@ static bool input_linux_check_toggle(InputLinux *il)
         return il->keydown[KEY_LEFTALT] &&
             il->keydown[KEY_RIGHTALT];
 
+    case GRAB_TOGGLE_KEYS_SHIFT_SHIFT:
+        return il->keydown[KEY_LEFTSHIFT] &&
+            il->keydown[KEY_RIGHTSHIFT];
+
     case GRAB_TOGGLE_KEYS_META_META:
         return il->keydown[KEY_LEFTMETA] &&
             il->keydown[KEY_RIGHTMETA];