fsnotify: add correlations between events

As part of the standard inotify events it includes a correlation cookie
between two dentry move operations.  This patch includes the same behaviour
in fsnotify events.  It is needed so that inotify userspace can be
implemented on top of fsnotify.

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, 21 insertions, 5 deletions

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 675129fa9fd..f11d75f0236 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -115,7 +115,7 @@ void __fsnotify_parent(struct dentry *dentry, __u32 mask)
 		mask |= FS_EVENT_ON_CHILD;
 
 		fsnotify(p_inode, mask, dentry->d_inode, FSNOTIFY_EVENT_INODE,
-			 dentry->d_name.name);
+			 dentry->d_name.name, 0);
 		dput(parent);
 	}
 
@@ -132,7 +132,7 @@ EXPORT_SYMBOL_GPL(__fsnotify_parent);
  * out to all of the registered fsnotify_group.  Those groups can then use the
  * notification event in whatever means they feel necessary.
  */
-void fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is, const char *file_name)
+void fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is, const char *file_name, u32 cookie)
 {
 	struct fsnotify_group *group;
 	struct fsnotify_event *event = NULL;
@@ -157,7 +157,7 @@ void fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is, const
 			if (!group->ops->should_send_event(group, to_tell, mask))
 				continue;
 			if (!event) {
-				event = fsnotify_create_event(to_tell, mask, data, data_is, file_name);
+				event = fsnotify_create_event(to_tell, mask, data, data_is, file_name, cookie);
 				/* shit, we OOM'd and now we can't tell, maybe
 				 * someday someone else will want to do something
 				 * here */
diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index c69b18b9aba..346f6e5c355 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -35,6 +35,7 @@
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/list.h>
+#include <linux/module.h>
 #include <linux/mount.h>
 #include <linux/mutex.h>
 #include <linux/namei.h>
@@ -56,6 +57,17 @@ static struct kmem_cache *fsnotify_event_holder_cachep;
  * get set to 0 so it will never get 'freed'
  */
 static struct fsnotify_event q_overflow_event;
+static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
+
+/**
+ * fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
+ * Called from fsnotify_move, which is inlined into filesystem modules.
+ */
+u32 fsnotify_get_cookie(void)
+{
+	return atomic_inc_return(&fsnotify_sync_cookie);
+}
+EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
 
 /* return true if the notify queue is empty, false otherwise */
 bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
@@ -266,6 +278,8 @@ static void initialize_event(struct fsnotify_event *event)
 
 	event->file_name = NULL;
 	event->name_len = 0;
+
+	event->sync_cookie = 0;
 }
 
 /*
@@ -280,8 +294,8 @@ static void initialize_event(struct fsnotify_event *event)
  * @data_type flag indication if the data is a file, path, inode, nothing...
  * @name the filename, if available
  */
-struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask,
-					     void *data, int data_type, const char *name)
+struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, void *data,
+					     int data_type, const char *name, u32 cookie)
 {
 	struct fsnotify_event *event;
 
@@ -299,6 +313,8 @@ struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask,
 		}
 		event->name_len = strlen(event->file_name);
 	}
+
+	event->sync_cookie = cookie;
 	event->to_tell = to_tell;
 
 	switch (data_type) {