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Subject[patch] add two inotify_add_watch flags
From
Date
Yo,

The below patch lets user space 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>
Index: linux-2.6.14-rc5/fs/inotify.c
===================================================================
--- linux-2.6.14-rc5.orig/fs/inotify.c 2005-10-20 02:23:05.000000000 -0400
+++ linux-2.6.14-rc5/fs/inotify.c 2005-12-06 19:01:22.000000000 -0500
@@ -363,11 +363,18 @@
/*
* 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,
+ int only_dir, int dont_follow_symlink)
{
int error;
+ unsigned flags = 0;

- error = __user_walk(dirname, LOOKUP_FOLLOW, nd);
+ if (!dont_follow_symlink)
+ flags |= LOOKUP_FOLLOW;
+ if (only_dir)
+ flags |= LOOKUP_DIRECTORY;
+
+ error = __user_walk(dirname, flags, nd);
if (error)
return error;
/* you can only watch an inode if you have read permissions on it */
@@ -943,7 +950,7 @@
goto fput_and_out;
}

- ret = find_inode(path, &nd);
+ ret = find_inode(path, &nd, mask & IN_ONLYDIR, mask & IN_DONT_FOLLOW);
if (unlikely(ret))
goto fput_and_out;

Index: linux-2.6.14-rc5/include/linux/inotify.h
===================================================================
--- linux-2.6.14-rc5.orig/include/linux/inotify.h 2005-10-20 02:23:05.000000000 -0400
+++ linux-2.6.14-rc5/include/linux/inotify.h 2005-12-06 18:57:11.000000000 -0500
@@ -47,6 +47,8 @@
#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 */
-
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