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, 6 insertions, 0 deletions

diff --git a/fs/notify/fsnotify.h b/fs/notify/fsnotify.h
index 5bd22412017f..2ba59158969f 100644
--- a/fs/notify/fsnotify.h
+++ b/fs/notify/fsnotify.h
@@ -10,14 +10,20 @@
 extern struct srcu_struct fsnotify_grp_srcu;
 /* all groups which receive inode fsnotify events */
 extern struct list_head fsnotify_inode_groups;
+/* all groups which receive vfsmount fsnotify events */
+extern struct list_head fsnotify_vfsmount_groups;
 /* all bitwise OR of all event types (FS_*) for all fsnotify_inode_groups */
 extern __u32 fsnotify_inode_mask;
+/* all bitwise OR of all event types (FS_*) for all fsnotify_vfsmount_groups */
+extern __u32 fsnotify_vfsmount_mask;
 
 /* destroy all events sitting in this groups notification queue */
 extern void fsnotify_flush_notify(struct fsnotify_group *group);
 
 /* add a group to the inode group list */
 extern void fsnotify_add_inode_group(struct fsnotify_group *group);
+/* add a group to the vfsmount group list */
+extern void fsnotify_add_vfsmount_group(struct fsnotify_group *group);
 /* final kfree of a group */
 extern void fsnotify_final_destroy_group(struct fsnotify_group *group);