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, 29 insertions, 4 deletions

diff --git a/fs/notify/group.c b/fs/notify/group.c
index 34fccbd2809c..aa4654fe6ec2 100644
--- a/fs/notify/group.c
+++ b/fs/notify/group.c
@@ -32,10 +32,14 @@
 static DEFINE_MUTEX(fsnotify_grp_mutex);
 /* protects reads while running the fsnotify_groups list */
 struct srcu_struct fsnotify_grp_srcu;
-/* all groups registered to receive filesystem notifications */
+/* all groups registered to receive inode filesystem notifications */
 LIST_HEAD(fsnotify_inode_groups);
+/* all groups registered to receive mount point filesystem notifications */
+LIST_HEAD(fsnotify_vfsmount_groups);
 /* bitwise OR of all events (FS_*) interesting to some group on this system */
 __u32 fsnotify_inode_mask;
+/* bitwise OR of all events (FS_*) interesting to some group on this system */
+__u32 fsnotify_vfsmount_mask;
 
 /*
  * When a new group registers or changes it's set of interesting events
@@ -44,14 +48,20 @@ __u32 fsnotify_inode_mask;
 void fsnotify_recalc_global_mask(void)
 {
         struct fsnotify_group *group;
-        __u32 mask = 0;
+        __u32 inode_mask = 0;
+        __u32 vfsmount_mask = 0;
         int idx;
 
         idx = srcu_read_lock(&fsnotify_grp_srcu);
         list_for_each_entry_rcu(group, &fsnotify_inode_groups, inode_group_list)
-                mask |= group->mask;
+                inode_mask |= group->mask;
+        list_for_each_entry_rcu(group, &fsnotify_vfsmount_groups, vfsmount_group_list)
+                vfsmount_mask |= group->mask;
+                
         srcu_read_unlock(&fsnotify_grp_srcu, idx);
-        fsnotify_inode_mask = mask;
+
+        fsnotify_inode_mask = inode_mask;
+        fsnotify_vfsmount_mask = vfsmount_mask;
 }
 
 /*
@@ -77,6 +87,17 @@ void fsnotify_recalc_group_mask(struct fsnotify_group *group)
                 fsnotify_recalc_global_mask();
 }
 
+void fsnotify_add_vfsmount_group(struct fsnotify_group *group)
+{
+        mutex_lock(&fsnotify_grp_mutex);
+
+        if (!group->on_vfsmount_group_list)
+                list_add_tail_rcu(&group->vfsmount_group_list, &fsnotify_vfsmount_groups);
+        group->on_vfsmount_group_list = 1;
+
+        mutex_unlock(&fsnotify_grp_mutex);
+}
+
 void fsnotify_add_inode_group(struct fsnotify_group *group)
 {
         mutex_lock(&fsnotify_grp_mutex);
@@ -132,6 +153,9 @@ static void __fsnotify_evict_group(struct fsnotify_group *group)
         if (group->on_inode_group_list)
                 list_del_rcu(&group->inode_group_list);
         group->on_inode_group_list = 0;
+        if (group->on_vfsmount_group_list)
+                list_del_rcu(&group->vfsmount_group_list);
+        group->on_vfsmount_group_list = 0;
 }
 
 /*
@@ -197,6 +221,7 @@ struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops)
         group->max_events = UINT_MAX;
 
         INIT_LIST_HEAD(&group->inode_group_list);
+        INIT_LIST_HEAD(&group->vfsmount_group_list);
 
         spin_lock_init(&group->mark_lock);
         INIT_LIST_HEAD(&group->mark_entries);