diff --git a/fs/notify/notification.c b/fs/notify/notification.c index bc9470c7ece7..b493c378445f 100644 --- a/fs/notify/notification.c +++ b/fs/notify/notification.c @@ -287,6 +287,62 @@ static void initialize_event(struct fsnotify_event *event) INIT_LIST_HEAD(&event->private_data_list); } +/* + * Caller damn well better be holding whatever mutex is protecting the + * old_holder->event_list. + */ +int fsnotify_replace_event(struct fsnotify_event_holder *old_holder, + struct fsnotify_event *new_event) +{ + struct fsnotify_event *old_event = old_holder->event; + struct fsnotify_event_holder *new_holder = NULL; + + /* + * 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 + * holder. + * For the overflow event it's possible that something will use the in + * event holder before we get the lock so we may need to jump back and + * alloc a new holder, this can't happen for most events... + */ + if (!list_empty(&new_event->holder.event_list)) { +alloc_holder: + new_holder = fsnotify_alloc_event_holder(); + if (!new_holder) + return -ENOMEM; + } + + spin_lock(&old_event->lock); + spin_lock(&new_event->lock); + + if (list_empty(&new_event->holder.event_list)) { + if (unlikely(new_holder)) + fsnotify_destroy_event_holder(new_holder); + new_holder = &new_event->holder; + } else if (unlikely(!new_holder)) { + /* between the time we checked above and got the lock the in + * event holder was used, go back and get a new one */ + spin_unlock(&new_event->lock); + spin_unlock(&old_event->lock); + goto alloc_holder; + } + + new_holder->event = new_event; + list_replace_init(&old_holder->event_list, &new_holder->event_list); + + spin_unlock(&new_event->lock); + spin_unlock(&old_event->lock); + + /* event == holder means we are referenced through the in event holder */ + if (old_holder != &old_event->holder) + fsnotify_destroy_event_holder(old_holder); + + fsnotify_get_event(new_event); /* on the list take reference */ + fsnotify_put_event(old_event); /* off the list, drop reference */ + + return 0; +} + struct fsnotify_event *fsnotify_clone_event(struct fsnotify_event *old_event) { struct fsnotify_event *event; diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h index 3a7fff235539..427f6ffab127 100644 --- a/include/linux/fsnotify_backend.h +++ b/include/linux/fsnotify_backend.h @@ -365,6 +365,8 @@ extern struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 /* fanotify likes to change events after they are on lists... */ extern struct fsnotify_event *fsnotify_clone_event(struct fsnotify_event *old_event); +extern int fsnotify_replace_event(struct fsnotify_event_holder *old_holder, + struct fsnotify_event *new_event); #else