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, 70 insertions, 22 deletions

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 23b5cfb..a61aaa7 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -21,6 +21,7 @@
 #include <linux/gfp.h>
 #include <linux/init.h>
 #include <linux/module.h>
+#include <linux/mount.h>
 #include <linux/srcu.h>
 
 #include <linux/fsnotify_backend.h>
@@ -134,6 +135,45 @@ void __fsnotify_parent(struct file *file, struct dentry *dentry, __u32 mask)
 }
 EXPORT_SYMBOL_GPL(__fsnotify_parent);
 
+static void send_to_group(__u32 mask,
+			  struct fsnotify_group *group,
+			  void *data, int data_is, const char *file_name,
+			  u32 cookie, struct fsnotify_event **event,
+			  struct inode *to_tell)
+{
+	if (!group->ops->should_send_event(group, to_tell, mask,
+					   data, data_is))
+		return;
+	if (!*event) {
+		*event = fsnotify_create_event(to_tell, mask, data,
+						data_is, file_name,
+						cookie, GFP_KERNEL);
+		/*
+		 * shit, we OOM'd and now we can't tell, maybe
+		 * someday someone else will want to do something
+		 * here
+		 */
+		if (!*event)
+			return;
+	}
+	group->ops->handle_event(group, *event);
+}
+
+static bool needed_by_vfsmount(__u32 test_mask, void *data, int data_is)
+{
+	struct path *path;
+
+	if (data_is == FSNOTIFY_EVENT_PATH)
+		path = (struct path *)data;
+	else if (data_is == FSNOTIFY_EVENT_FILE)
+		path = &((struct file *)data)->f_path;
+	else
+		return false;
+
+	/* hook in this when mnt->mnt_fsnotify_mask is defined */
+	/* return (test_mask & path->mnt->mnt_fsnotify_mask); */
+	return false;
+}
 /*
  * This is the main call to fsnotify.  The VFS calls into hook specific functions
  * in linux/fsnotify.h.  Those functions then in turn call here.  Here will call
@@ -148,38 +188,46 @@ void fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is, const
 	/* global tests shouldn't care about events on child only the specific event */
 	__u32 test_mask = (mask & ~FS_EVENT_ON_CHILD);
 
-	if (list_empty(&fsnotify_inode_groups))
-		return;
+	/* if no fsnotify listeners, nothing to do */
+	if (list_empty(&fsnotify_inode_groups) &&
+	    list_empty(&fsnotify_vfsmount_groups))
+                return;
+ 
+	/* if none of the directed listeners or vfsmount listeners care */
+	if (!(test_mask & fsnotify_inode_mask) &&
+	    !(test_mask & fsnotify_vfsmount_mask))
+                return;
+ 
+	/* if this inode's directed listeners don't care and nothing on the vfsmount
+	 * listeners list cares, nothing to do */
+	if (!(test_mask & to_tell->i_fsnotify_mask) &&
+	    !needed_by_vfsmount(test_mask, data, data_is))
+                return;
 
-	if (!(test_mask & fsnotify_inode_mask))
-		return;
-
-	if (!(test_mask & to_tell->i_fsnotify_mask))
-		return;
 	/*
 	 * SRCU!!  the groups list is very very much read only and the path is
 	 * very hot.  The VAST majority of events are not going to need to do
 	 * anything other than walk the list so it's crazy to pre-allocate.
 	 */
 	idx = srcu_read_lock(&fsnotify_grp_srcu);
-	list_for_each_entry_rcu(group, &fsnotify_inode_groups, inode_group_list) {
-		if (test_mask & group->mask) {
-			if (!group->ops->should_send_event(group, to_tell, mask,
-							   data, data_is))
-				continue;
-			if (!event) {
-				event = fsnotify_create_event(to_tell, mask, data,
-							      data_is, file_name, cookie,
-							      GFP_KERNEL);
-				/* shit, we OOM'd and now we can't tell, maybe
-				 * someday someone else will want to do something
-				 * here */
-				if (!event)
-					break;
+
+	if (test_mask & to_tell->i_fsnotify_mask) {
+		list_for_each_entry_rcu(group, &fsnotify_inode_groups, inode_group_list) {
+			if (test_mask & group->mask) {
+				send_to_group(mask, group, data, data_is,
+					      file_name, cookie, &event, to_tell);
 			}
-			group->ops->handle_event(group, event);
 		}
 	}
+	if (needed_by_vfsmount(test_mask, data, data_is)) {
+		list_for_each_entry_rcu(group, &fsnotify_vfsmount_groups, vfsmount_group_list) {
+			if (test_mask & group->mask) {
+				send_to_group(mask, group, data, data_is,
+					      file_name, cookie, &event, to_tell);
+			}
+		}
+	}
+
 	srcu_read_unlock(&fsnotify_grp_srcu, idx);
 	/*
 	 * fsnotify_create_event() took a reference so the event can't be cleaned