fsnotify: allow groups to add private data to events

inotify needs per group information attached to events.  This patch allows
groups to attach private information and implements a callback so that
information can be freed when an event is being destroyed.

Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>

2 files changed, 49 insertions, 4 deletions

diff --git a/fs/notify/dnotify/dnotify.c b/fs/notify/dnotify/dnotify.c
index d9d80f502c6f..12f9e6b1ffe2 100644
--- a/fs/notify/dnotify/dnotify.c
+++ b/fs/notify/dnotify/dnotify.c
@@ -183,6 +183,7 @@ static struct fsnotify_ops dnotify_fsnotify_ops = {
         .should_send_event = dnotify_should_send_event,
         .free_group_priv = NULL,
         .freeing_mark = dnotify_freeing_mark,
+        .free_event_priv = NULL,
 };
 
 /*
diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index 346f6e5c3553..959b73e756fd 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -90,6 +90,8 @@ void fsnotify_put_event(struct fsnotify_event *event)
                 if (event->data_type == FSNOTIFY_EVENT_PATH)
                         path_put(&event->path);
 
+                BUG_ON(!list_empty(&event->private_data_list));
+
                 kfree(event->file_name);
                 kmem_cache_free(fsnotify_event_cachep, event);
         }
@@ -106,7 +108,29 @@ void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder)
 }
 
 /*
- * check if 2 events contain the same information.
+ * Find the private data that the group previously attached to this event when
+ * the group added the event to the notification queue (fsnotify_add_notify_event)
+ */
+struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnotify_group *group, struct fsnotify_event *event)
+{
+        struct fsnotify_event_private_data *lpriv;
+        struct fsnotify_event_private_data *priv = NULL;
+
+        assert_spin_locked(&event->lock);
+
+        list_for_each_entry(lpriv, &event->private_data_list, event_list) {
+                if (lpriv->group == group) {
+                        priv = lpriv;
+                        list_del(&priv->event_list);
+                        break;
+                }
+        }
+        return priv;
+}
+
+/*
+ * Check if 2 events contain the same information.  We do not compare private data
+ * but at this moment that isn't a problem for any know fsnotify listeners.
  */
 static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new)
 {
@@ -134,13 +158,17 @@ static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new
  * event off the queue to deal with.  If the event is successfully added to the
  * group's notification queue, a reference is taken on event.
  */
-int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event)
+int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
+                              struct fsnotify_event_private_data *priv)
 {
         struct fsnotify_event_holder *holder = NULL;
         struct list_head *list = &group->notification_list;
         struct fsnotify_event_holder *last_holder;
         struct fsnotify_event *last_event;
 
+        /* easy to tell if priv was attached to the event */
+        INIT_LIST_HEAD(&priv->event_list);
+
         /*
          * There is one fsnotify_event_holder embedded inside each fsnotify_event.
          * Check if we expect to be able to use that holder.  If not alloc a new
@@ -158,8 +186,11 @@ alloc_holder:
 
         mutex_lock(&group->notification_mutex);
 
-        if (group->q_len >= group->max_events)
+        if (group->q_len >= group->max_events) {
                 event = &q_overflow_event;
+                /* sorry, no private data on the overflow event */
+                priv = NULL;
+        }
 
         spin_lock(&event->lock);
 
@@ -183,7 +214,7 @@ alloc_holder:
                         mutex_unlock(&group->notification_mutex);
                         if (holder != &event->holder)
                                 fsnotify_destroy_event_holder(holder);
-                        return 0;
+                        return -EEXIST;
                 }
         }
 
@@ -192,6 +223,8 @@ alloc_holder:
 
         fsnotify_get_event(event);
         list_add_tail(&holder->event_list, list);
+        if (priv)
+                list_add_tail(&priv->event_list, &event->private_data_list);
         spin_unlock(&event->lock);
         mutex_unlock(&group->notification_mutex);
 
@@ -252,10 +285,19 @@ struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group)
 void fsnotify_flush_notify(struct fsnotify_group *group)
 {
         struct fsnotify_event *event;
+        struct fsnotify_event_private_data *priv;
 
         mutex_lock(&group->notification_mutex);
         while (!fsnotify_notify_queue_is_empty(group)) {
                 event = fsnotify_remove_notify_event(group);
+                /* if they don't implement free_event_priv they better not have attached any */
+                if (group->ops->free_event_priv) {
+                        spin_lock(&event->lock);
+                        priv = fsnotify_remove_priv_from_event(group, event);
+                        spin_unlock(&event->lock);
+                        if (priv)
+                                group->ops->free_event_priv(priv);
+                }
                 fsnotify_put_event(event); /* matches fsnotify_add_notify_event */
         }
         mutex_unlock(&group->notification_mutex);
@@ -274,6 +316,8 @@ static void initialize_event(struct fsnotify_event *event)
         event->inode = NULL;
         event->data_type = FSNOTIFY_EVENT_NONE;
 
+        INIT_LIST_HEAD(&event->private_data_list);
+
         event->to_tell = NULL;
 
         event->file_name = NULL;