Send CHANGES_DONE_HINT on file moves if no IN_CLOSE_WRITE is emitted

This patch makes GFileMonitor to emit EVENT_CHANGES_DONE_HINT when
EVENT_CREATED is emitted but the file is not opened for writing.

On file moves across different mounted volumes, inotify will always emit
IN_CREATE and IN_CLOSE_WRITE (plus other events).
This translates into GIO's _EVENT_CREATED and _EVENT_CHANGES_DONE_HINT.

On file moves across the same mounted volumes, inotify will emit
IN_MOVED_FROM/IN_MOVED_TO which will be translated into
_EVENT_DELETED/_EVENT_CREATED GIO's side. No _EVENT_CHANGES_DONE_HINT is
emited afterwards.
Under such circumstances a file indexer does not know when actually the
file is ready to be indexed, either waiting too much or triggering the
indexing twice. On small devices it's not advisable.

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=640077
Bug-NB: NB#219982
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Reviewed-by: Tomas Bzatek <tbzatek@redhat.com>

gio/inotify/inotify-helper.c

@@ -190,6 +190,30 @@ ih_event_callback (ik_event_t  *event,
   g_file_monitor_emit_event (G_FILE_MONITOR (sub->user_data),
 			     child, other, eflags);
 
+  /* For paired moves or moves whose mask has been changed from IN_MOVED_TO to
+   * IN_CREATE, notify also that it's probably the last change to the file,
+   * emitting CHANGES_DONE_HINT.
+   * The first (first part of the if's guard below) is the case of a normal
+   * move within the monitored tree and in the same mounted volume.
+   * The latter (second part of the guard) is the case of a move within the
+   * same mounted volume, but from a not monitored directory.
+   *
+   * It's not needed in cases like moves across mounted volumes as the IN_CREATE
+   * will be followed by a IN_MODIFY and IN_CLOSE_WRITE events.
+   * Also not needed if sub->pair_moves is set as EVENT_MOVED will be emitted
+   * instead of EVENT_CREATED which implies no further modification will be
+   * applied to the file
+   * See: https://bugzilla.gnome.org/show_bug.cgi?id=640077
+   */
+  if ((!sub->pair_moves &&
+        event->is_second_in_pair && (event->mask & IN_MOVED_TO)) ||
+      (!ih_event_is_paired_move (event) &&
+       (event->original_mask & IN_MOVED_TO) && (event->mask & IN_CREATE)))
+    {
+      g_file_monitor_emit_event (G_FILE_MONITOR (sub->user_data),
+          child, NULL, G_FILE_MONITOR_EVENT_CHANGES_DONE_HINT);
+    }
+
   g_object_unref (child);
   if (other)
     g_object_unref (other);

gio/inotify/inotify-kernel.c

@@ -516,6 +516,7 @@ ik_pair_events (ik_event_internal_t *event1,
   /* Pair the internal structures and the ik_event_t structures */
   event1->pair = event2;
   event1->event->pair = event2->event;
+  event2->event->is_second_in_pair = TRUE;
   
   if (g_timeval_lt (&event1->hold_until, &event2->hold_until))
     event1->hold_until = event2->hold_until;
@@ -634,7 +635,8 @@ ik_process_events (void)
 	   * the event masks */
 	  /* Changeing MOVED_FROM to DELETE and MOVED_TO to create lets us make
 	   * the gaurantee that you will never see a non-matched MOVE event */
-	  
+	  event->event->original_mask = event->event->mask;
+
 	  if (event->event->mask & IN_MOVED_FROM)
 	    {
 	      event->event->mask = IN_DELETE|(event->event->mask & IN_ISDIR);

gio/inotify/inotify-kernel.h

@@ -26,9 +26,17 @@
 typedef struct ik_event_s {
   gint32 wd;
   guint32 mask;
+  guint32 original_mask;
   guint32 cookie;
   guint32 len;
   char *  name;
+  /* TRUE if this event is the last element of a pair
+   * (e.g., MOVE_TO in a pair of MOVE_FROM, MOVE_TO events) */
+  gboolean is_second_in_pair;
+  /* if event1 and event2 are two paired events
+   * (e.g., MOVE_FROM and MOVE_TO events related to the same file move),
+   * then event1->pair == event2 and event2->pair == NULL.
+   * It will result also in event1->pair->is_second_in_pair == TRUE */
   struct ik_event_s *pair;
 } ik_event_t;