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 <[email protected]>
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 */
On Tue, 2005-12-06 at 22:54 -0500, John McCutchan wrote:
> 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.
Looks good to me, and I confirm we hit these issues in real-life with
gnome-vfs.
Acked-by: Robert Love <[email protected]>
Robert Love
John McCutchan <[email protected]> wrote:
>
> -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;
I'd have thought that it'd be more general to pass the __user_walk flags
into find_inode(), rather than calculating them in the callee. Slightly
more efficient too.
On Fri, 2005-09-12 at 14:51 -0800, Andrew Morton wrote:
> John McCutchan <[email protected]> wrote:
> >
> > -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;
>
> I'd have thought that it'd be more general to pass the __user_walk flags
> into find_inode(), rather than calculating them in the callee. Slightly
> more efficient too.
Makes sense.
Signed-off-by: John McCutchan <[email protected]>
Index: linux-2.6.14-rc5/fs/inotify.c
===================================================================
--- linux-2.6.14-rc5.orig/fs/inotify.c 2005-12-09 17:59:10.000000000 -0500
+++ linux-2.6.14-rc5/fs/inotify.c 2005-12-09 18:04:22.000000000 -0500
@@ -363,11 +363,12 @@
/*
* 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 */
@@ -932,6 +933,7 @@
struct file *filp;
int ret, fput_needed;
int mask_add = 0;
+ unsigned flags = 0;
filp = fget_light(fd, &fput_needed);
if (unlikely(!filp))
@@ -943,7 +945,12 @@
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;
Index: linux-2.6.14-rc5/include/linux/inotify.h
===================================================================
--- linux-2.6.14-rc5.orig/include/linux/inotify.h 2005-12-09 17:59:10.000000000 -0500
+++ linux-2.6.14-rc5/include/linux/inotify.h 2005-12-09 18:00:49.000000000 -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 */