fsnotify: generic notification queue and waitq

inotify needs to do asyc notification in which event information is stored
on a queue until the listener is ready to receive it.  This patch
implements a generic notification queue for inotify (and later fanotify) to
store events to be sent at a later time.

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

1 files changed, 37 insertions, 0 deletions

diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 9ea800e840f1..15f8f82a5c57 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -119,6 +119,13 @@ struct fsnotify_group {
 
         const struct fsnotify_ops *ops; /* how this group handles things */
 
+        /* needed to send notification to userspace */
+        struct mutex notification_mutex;        /* protect the notification_list */
+        struct list_head notification_list;     /* list of event_holder this group needs to send to userspace */
+        wait_queue_head_t notification_waitq;   /* read() on the notification file blocks on this waitq */
+        unsigned int q_len;                     /* events on the queue */
+        unsigned int max_events;                /* maximum events allowed on the list */
+
         /* stores all fastapth entries assoc with this group so they can be cleaned on unregister */
         spinlock_t mark_lock;           /* protect mark_entries list */
         atomic_t num_marks;             /* 1 for each mark entry and 1 for not being
@@ -136,11 +143,32 @@ struct fsnotify_group {
 };
 
 /*
+ * A single event can be queued in multiple group->notification_lists.
+ *
+ * each group->notification_list will point to an event_holder which in turns points
+ * to the actual event that needs to be sent to userspace.
+ *
+ * Seemed cheaper to create a refcnt'd event and a small holder for every group
+ * than create a different event for every group
+ *
+ */
+struct fsnotify_event_holder {
+        struct fsnotify_event *event;
+        struct list_head event_list;
+};
+
+/*
  * all of the information about the original object we want to now send to
  * a group.  If you want to carry more info from the accessing task to the
  * listener this structure is where you need to be adding fields.
  */
 struct fsnotify_event {
+        /*
+         * If we create an event we are also likely going to need a holder
+         * to link to a group.  So embed one holder in the event.  Means only
+         * one allocation for the common case where we only have one group
+         */
+        struct fsnotify_event_holder holder;
         spinlock_t lock;        /* protection for the associated event_holder and private_list */
         /* to_tell may ONLY be dereferenced during handle_event(). */
         struct inode *to_tell;  /* either the inode the event happened to or its parent */
@@ -264,6 +292,15 @@ extern void fsnotify_put_event(struct fsnotify_event *event);
 extern struct fsnotify_event_private_data *fsnotify_get_priv_from_event(struct fsnotify_group *group,
                                                                         struct fsnotify_event *event);
 
+/* attach the event to the group notification queue */
+extern int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event);
+/* true if the group notification queue is empty */
+extern bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group);
+/* return, but do not dequeue the first event on the notification queue */
+extern struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group);
+/* reutnr AND dequeue the first event on the notification queue */
+extern struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group);
+
 /* functions used to manipulate the marks attached to inodes */
 
 /* run all marks associated with an inode and update inode->i_fsnotify_mask */