[mutter/session-try-sd-pid: 3/3] launcher: First check if we are in a login session

[Iain Lane <iainl src gnome org>]

commit 89162a90aadce266a17fc67aa03162e473adb2e0
Author: Iain Lane <iainl gnome org>
Date:   Mon Jul 9 10:20:47 2018 +0100

    launcher: First check if we are in a login session
    
    For mutter developers we still want to support running from a VT, which
    will be in a different login session.
    
    Fixes #218

 src/backends/native/meta-launcher.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
---
diff --git a/src/backends/native/meta-launcher.c b/src/backends/native/meta-launcher.c
index 15cad0d40..fb12b0cf5 100644
--- a/src/backends/native/meta-launcher.c
+++ b/src/backends/native/meta-launcher.c
@@ -79,6 +79,29 @@ find_systemd_session (gchar **session_id,
   g_assert (session_id != NULL);
   g_assert (error == NULL || *error == NULL);
 
+  /* if we are in a logind session, we can trust that value, so use it. This
+   * happens for example when you run mutter directly from a VT but when
+   * systemd starts us we will not be in a logind session. */
+  saved_errno = sd_pid_get_session (0, &local_session_id);
+  if (saved_errno < 0)
+    {
+      if (saved_errno != -ENODATA)
+        {
+          g_set_error (error,
+                       G_IO_ERROR,
+                       G_IO_ERROR_NOT_FOUND,
+                       "Failed to get session by pid for user %d (%s)",
+                       getuid (),
+                       g_strerror (-saved_errno));
+          return FALSE;
+        }
+    }
+  else
+    {
+      *session_id = g_steal_pointer (&local_session_id);
+      return TRUE;
+    }
+
   saved_errno = sd_uid_get_display (getuid (), &local_session_id);
   if (saved_errno < 0)
     {