[Xwayland] Check for listenfd option (#743)

* [Wayland] Add Xwayland byte-swapped clients support

Recent versions of Xwayland can allow or disallow X11 clients from
different endianess to connect.
Add a setting to configure this feature from Muffin, who spawns
Xwayland.

Disabled by default, since this feature have potential
security issues.

* Use args for Xwayland and explicit disable byte swapped clients

* Typo

* [Xwayland] Check for listenfd option

`-listen` is deprecated in modern versions of Xwayland and replaced
by `-listenfd`. Use the pkg-config variable "have_listenfd" (if available) from Xwayland
to determine if we should use that option, to avoid a deprecation
warning when spawning Xwayland.

Author: Sunderland93

config.h.meson

@@ -71,5 +71,8 @@
 /* Whether Xwayland has -initfd option */
 #mesondefine HAVE_XWAYLAND_INITFD
 
+/* Whether Xwayland has -listenfd option */
+#mesondefine HAVE_XWAYLAND_LISTENFD
+
 /* Whether the Xwayland supports +/-byteswappedclients */
 #mesondefine HAVE_XWAYLAND_BYTE_SWAPPED_CLIENTS

meson.build

@@ -376,6 +376,8 @@ if cc.has_header_symbol('sys/prctl.h', 'prctl')
 endif
 
 have_xwayland_initfd = false
+have_xwayland_listenfd = false
+
 have_xwayland_byte_swapped_clients = false
 if have_wayland
   xwayland_dep = dependency('xwayland', required: false)
@@ -418,6 +420,15 @@ if have_wayland
     cdata.set('HAVE_XWAYLAND_INITFD', 1)
   endif
 
+    # For Xwayland -listenfd usage
+  if xwayland_dep.found()
+    have_xwayland_listenfd = xwayland_dep.get_pkgconfig_variable('have_listenfd') == 'true'
+  endif
+
+  if (have_xwayland_listenfd)
+    cdata.set('HAVE_XWAYLAND_LISTENFD', 1)
+  endif
+
     # For Xwayland +/-byteswappedclients usage
   if xwayland_dep.found()
     have_xwayland_byte_swapped_clients = xwayland_dep.get_variable('have_byteswappedclients',
@@ -489,6 +500,7 @@ output = [
   '        Introspection.................... ' + have_introspection.to_string(),
   '        Profiler......................... ' + have_profiler.to_string(),
   '        Xwayland initfd.................. ' + have_xwayland_initfd.to_string(),
+  '        Xwayland listenfd................ ' + have_xwayland_listenfd.to_string(),
   '        Xwayland byte-swapped clients.... ' + have_xwayland_byte_swapped_clients.to_string(),
   '',
   '    Tests:',

src/wayland/meta-xwayland.c

@@ -44,6 +44,12 @@
 #include "wayland/meta-xwayland-surface.h"
 #include "x11/meta-x11-display-private.h"
 
+#ifdef HAVE_XWAYLAND_LISTENFD
+#define XWAYLAND_LISTENFD "-listenfd"
+#else
+#define XWAYLAND_LISTENFD "-listen"
+#endif
+
 static int display_number_override = -1;
 
 static void meta_xwayland_stop_xserver (MetaXWaylandManager *manager);
@@ -640,6 +646,9 @@ meta_xwayland_start_xserver (MetaXWaylandManager *manager,
   args[i++] = "-core";
   args[i++] = "-auth";
   args[i++] = manager->auth_file;
+  args[i++] = XWAYLAND_LISTENFD;
+  args[i++] = "4";
+  args[i++] = XWAYLAND_LISTENFD;
   args[i++] = "-listen";
   args[i++] = "4";
   args[i++] = "-listen";
@@ -650,7 +659,7 @@ meta_xwayland_start_xserver (MetaXWaylandManager *manager,
   args[i++] = "-initfd";
   args[i++] = "7";
 #else
-  args[i++] = "-listen";
+  args[i++] = XWAYLAND_LISTENFD;
   args[i++] = "7";
 #endif