realtime: Include PID/TID in some error messages

The PID is useful when debugging issues related to these messages,
so we can check whether the PID has some strange property
that caused the problem.

src/realtime.c

@@ -62,24 +62,25 @@ static gboolean
 map_pid (XdpAppInfo *app_info, pid_t *pid, pid_t *tid, GError **error)
 {
   ino_t pidns_id;
+  const pid_t unmapped_pid = *pid;
 
   if (!xdp_app_info_get_pidns (app_info, &pidns_id, error))
     {
-      g_prefix_error (error, "Could not get pidns: ");
+      g_prefix_error (error, "Could not get pidns for pid %d: ", unmapped_pid);
       g_warning ("Realtime error: %s", (*error)->message);
       return FALSE;
     }
 
   if (pidns_id != 0 && !xdp_map_pids (pidns_id, pid, 1, error))
     {
-      g_prefix_error (error, "Could not map pid: ");
+      g_prefix_error (error, "Could not map pid %d: ", unmapped_pid);
       g_warning ("Realtime error: %s", (*error)->message);
       return FALSE;
     }
 
   if (pidns_id != 0 && !xdp_map_tids (pidns_id, *pid, tid, 1, error))
     {
-      g_prefix_error (error, "Could not map tid: ");
+      g_prefix_error (error, "Could not map tid %d of pid %d: ", *tid, unmapped_pid);
       g_warning ("Realtime error: %s", (*error)->message);
       return FALSE;
     }