[PATCH] inotify: add two inotify_add_watch flags

The below patch lets userspace have more control over the inodes that
inotify will watch.  It introduces two new flags.

        IN_ONLYDIR -- only watch the inode if it is a directory.
        This is needed to avoid the race that can occur when we want to be
        sure that we are watching a directory.

        IN_DONT_FOLLOW -- don't follow a symlink.  In combination
        with IN_ONLYDIR we can make sure that we don't watch the target of
        symlinks.

The issues the flags fix came up when writing the gnome-vfs inotify
backend.  Default behaviour is unchanged.

Signed-off-by: John McCutchan <ttb@tentacle.dhs.org>
Acked-by: Robert Love <rml@novell.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 12 insertions, 3 deletions

diff --git a/fs/inotify.c b/fs/inotify.c
index bf7ce1d2412b..2fecb7af4a77 100644
--- a/fs/inotify.c
+++ b/fs/inotify.c
@@ -364,11 +364,12 @@ static int inotify_dev_get_wd(struct inotify_device *dev,
 /*
  * find_inode - resolve a user-given path to a specific inode and return a nd
  */
-static int find_inode(const char __user *dirname, struct nameidata *nd)
+static int find_inode(const char __user *dirname, struct nameidata *nd,
+                      unsigned flags)
 {
         int error;
 
-        error = __user_walk(dirname, LOOKUP_FOLLOW, nd);
+        error = __user_walk(dirname, flags, nd);
         if (error)
                 return error;
         /* you can only watch an inode if you have read permissions on it */
@@ -933,6 +934,7 @@ asmlinkage long sys_inotify_add_watch(int fd, const char __user *path, u32 mask)
         struct file *filp;
         int ret, fput_needed;
         int mask_add = 0;
+        unsigned flags = 0;
 
         filp = fget_light(fd, &fput_needed);
         if (unlikely(!filp))
@@ -944,7 +946,12 @@ asmlinkage long sys_inotify_add_watch(int fd, const char __user *path, u32 mask)
                 goto fput_and_out;
         }
 
-        ret = find_inode(path, &nd);
+        if (!(mask & IN_DONT_FOLLOW))
+                flags |= LOOKUP_FOLLOW;
+        if (mask & IN_ONLYDIR)
+                flags |= LOOKUP_DIRECTORY;
+
+        ret = find_inode(path, &nd, flags);
         if (unlikely(ret))
                 goto fput_and_out;
 
diff --git a/include/linux/inotify.h b/include/linux/inotify.h
index ee5b239092ed..267c88b5f742 100644
--- a/include/linux/inotify.h
+++ b/include/linux/inotify.h
@@ -47,6 +47,8 @@ struct inotify_event {
 #define IN_MOVE                 (IN_MOVED_FROM | IN_MOVED_TO) /* moves */
 
 /* special flags */
+#define IN_ONLYDIR              0x01000000      /* only watch the path if it is a directory */
+#define IN_DONT_FOLLOW          0x02000000      /* don't follow a sym link */
 #define IN_MASK_ADD             0x20000000      /* add to the mask of an already existing watch */
 #define IN_ISDIR                0x40000000      /* event occurred against dir */
 #define IN_ONESHOT              0x80000000      /* only send event once */