kernfs: make kernfs_notify() trigger inotify events too

kernfs_notify() is used to indicate either new data is available or
the content of a file has changed.  It currently only triggers poll
which may not be the most convenient to monitor especially when there
are a lot to monitor.  Let's hook it up to fsnotify too so that the
events can be monitored via inotify too.

fsnotify_modify() requires file * but kernfs_notify() doesn't have any
specific file associated; however, we can walk all super_blocks
associated with a kernfs_root and as kernfs always associate one ino
with inode and one dentry with an inode, it's trivial to look up the
dentry associated with a given kernfs_node.  As any active monitor
would pin dentry, just looking up existing dentry is enough.  This
patch looks up the dentry associated with the specified kernfs_node
and generates events equivalent to fsnotify_modify().

Note that as fsnotify doesn't provide fsnotify_modify() equivalent
which can be called with dentry, kernfs_notify() directly calls
fsnotify_parent() and fsnotify().  It might be better to add a wrapper
in fsnotify.h instead.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: John McCutchan <john@johnmccutchan.com>
Cc: Robert Love <rlove@rlove.org>
Cc: Eric Paris <eparis@parisplace.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 8034706..98bacd9 100644 (file)
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -14,6 +14,7 @@
 #include <linux/poll.h>
 #include <linux/pagemap.h>
 #include <linux/sched.h>
+#include <linux/fsnotify.h>
 
 #include "kernfs-internal.h"
 
@@ -785,20 +786,48 @@ static unsigned int kernfs_fop_poll(struct file *filp, poll_table *wait)
  */
 void kernfs_notify(struct kernfs_node *kn)
 {
+       struct kernfs_root *root = kernfs_root(kn);
        struct kernfs_open_node *on;
+       struct kernfs_super_info *info;
        unsigned long flags;
 
+       if (WARN_ON(kernfs_type(kn) != KERNFS_FILE))
+               return;
+
+       /* kick poll */
        spin_lock_irqsave(&kernfs_open_node_lock, flags);
 
-       if (!WARN_ON(kernfs_type(kn) != KERNFS_FILE)) {
-               on = kn->attr.open;
-               if (on) {
-                       atomic_inc(&on->event);
-                       wake_up_interruptible(&on->poll);
-               }
+       on = kn->attr.open;
+       if (on) {
+               atomic_inc(&on->event);
+               wake_up_interruptible(&on->poll);
        }
 
        spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
+
+       /* kick fsnotify */
+       mutex_lock(&kernfs_mutex);
+
+       list_for_each_entry(info, &root->supers, node) {
+               struct inode *inode;
+               struct dentry *dentry;
+
+               inode = ilookup(info->sb, kn->ino);
+               if (!inode)
+                       continue;
+
+               dentry = d_find_any_alias(inode);
+               if (dentry) {
+                       fsnotify_parent(NULL, dentry, FS_MODIFY);
+                       fsnotify(inode, FS_MODIFY, inode, FSNOTIFY_EVENT_INODE,
+                                NULL, 0);
+                       dput(dentry);
+               }
+
+               iput(inode);
+       }
+
+       mutex_unlock(&kernfs_mutex);
 }
 EXPORT_SYMBOL_GPL(kernfs_notify);