fsnotify: mount point listeners list and global mask

currently all of the notification systems implemented select which inodes
they care about and receive messages only about those inodes (or the
children of those inodes.)  This patch begins to flesh out fsnotify support
for the concept of listeners that want to hear notification for an inode
accessed below a given monut point.  This patch implements a second list
of fsnotify groups to hold these types of groups and a second global mask
to hold the events of interest for this type of group.

The reason we want a second group list and mask is because the inode based
notification should_send_event support which makes each group look for a mark
on the given inode.  With one nfsmount listener that means that every group would
have to take the inode->i_lock, look for their mark, not find one, and return
for every operation.   By seperating vfsmount from inode listeners only when
there is a inode listener will the inode groups have to look for their
mark and take the inode lock.  vfsmount listeners will have to grab the lock and
look for a mark but there should be fewer of them, and one vfsmount listener
won't cause the i_lock to be grabbed and released for every fsnotify group
on every io operation.

Signed-off-by: Eric Paris <eparis@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 21079ade562..dea48bee057 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -99,6 +99,10 @@ struct fsnotify_group {
 	 * or fsnotify_grp_srcu depending on write vs read.
 	 */
 	struct list_head inode_group_list;
+	/*
+	 * same as above except anchored by fsnotify_vfsmount_groups
+	 */
+	struct list_head vfsmount_group_list;
 
 	/*
 	 * Defines all of the event types in which this group is interested.
@@ -137,6 +141,7 @@ struct fsnotify_group {
 
 	/* prevents double list_del of group_list.  protected by global fsnotify_grp_mutex */
 	bool on_inode_group_list;
+	bool on_vfsmount_group_list;
 
 	/* groups can define private fields here or use the void *private */
 	union {