xwayland: Clean up display finding code

Split out and make it more manageable.

src/wayland/meta-xwayland.c

@@ -121,72 +121,100 @@ meta_xwayland_handle_wl_surface_id (MetaWindow *window,
     }
 }
 
-static char *
-create_lockfile (int display, int *display_out)
+static gboolean
+try_display (int    display,
+             char **filename_out,
+             int   *fd_out)
 {
+  gboolean ret = FALSE;
   char *filename;
-  int size;
-  char pid[11];
   int fd;
 
-  do
-    {
-      char *end;
-      pid_t other;
-
   filename = g_strdup_printf ("/tmp/.X%d-lock", display);
+
+ again:
   fd = open (filename, O_WRONLY | O_CLOEXEC | O_CREAT | O_EXCL, 0444);
 
   if (fd < 0 && errno == EEXIST)
     {
+      char pid[11];
+      char *end;
+      pid_t other;
+
       fd = open (filename, O_CLOEXEC, O_RDONLY);
       if (fd < 0 || read (fd, pid, 11) != 11)
         {
           g_warning ("can't read lock file %s: %m", filename);
-              g_free (filename);
-
-              /* ignore error and try the next display number */
-              display++;
-              continue;
+          goto out;
         }
       close (fd);
+      fd = -1;
 
       other = strtol (pid, &end, 0);
       if (end != pid + 10)
         {
           g_warning ("can't parse lock file %s", filename);
-              g_free (filename);
-
-              /* ignore error and try the next display number */
-              display++;
-              continue;
+          goto out;
         }
 
       if (kill (other, 0) < 0 && errno == ESRCH)
         {
+          /* Process is dead. Try unlinking the lockfile and trying again. */
           if (unlink (filename) < 0)
             {
               g_warning ("failed to unlink stale lock file %s: %m", filename);
-                  display++;
-                }
-              g_free (filename);
-              continue;
+              goto out;
             }
 
-          g_free (filename);
-          display++;
-          continue;
+          goto again;
+        }
+
+      goto out;
     }
   else if (fd < 0)
     {
       g_warning ("failed to create lock file %s: %m", filename);
-          g_free (filename);
-          return NULL;
+      goto out;
     }
 
-      break;
+  ret = TRUE;
+
+ out:
+  if (!ret)
+    {
+      g_free (filename);
+      filename = NULL;
+
+      if (fd >= 0)
+        {
+          close (fd);
+          fd = -1;
+        }
+    }
+
+  *filename_out = filename;
+  *fd_out = fd;
+  return ret;
+}
+
+static char *
+create_lockfile (int display, int *display_out)
+{
+  char *filename;
+  int fd;
+
+  char pid[11];
+  int size;
+
+  while (!try_display (display, &filename, &fd))
+    {
+      display++;
+
+      /* If display is above 50, then something's wrong. Just
+       * abort in this case. */
+      if (display > 50)
+        return NULL;
     }
-  while (1);
 
   /* Subtle detail: we use the pid of the wayland compositor, not the xserver
    * in the lock file. */