um: xterm: Add Wayland support

Under Wayland, we should check WAYLAND_DISPLAY instead.

Signed-off-by: Tiwei Bie <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Johannes Berg <[e-mail]>

arch/um/drivers/xterm.c

···
 	if (access(argv[4], X_OK) < 0)
 		argv[4] = "port-helper";
 
-	/*
-	 * Check that DISPLAY is set, this doesn't guarantee the xterm
-	 * will work but w/o it we can be pretty sure it won't.
-	 */
-	if (getenv("DISPLAY") == NULL) {
-		printk(UM_KERN_ERR "xterm_open: $DISPLAY not set.\n");
+	/* Ensure we are running on Xorg or Wayland. */
+	if (!getenv("DISPLAY") && !getenv("WAYLAND_DISPLAY")) {
+		printk(UM_KERN_ERR "xterm_open : neither $DISPLAY nor $WAYLAND_DISPLAY is set.\n");
 		return -ENODEV;
 	}