[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>

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;
 

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 */