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>

1 files changed, 35 insertions, 6 deletions

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 8034706a7af8..98bacd9ea7fd 100644
--- 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);