[PATCH 24/28] VFS: Fixup for ->follow_link on root of filesystem

[Mike Waychison <michael.waychison@sun.com>]

When a follow_link dentry call is made, the implementation expects the
dentry to be followed as well as a nameidata struct to be filled in.
The received nd->mnt is expected to contain the vfsmount of the dentry
being followed, so that a subsequent call to vfs_follow_link may
properly pivot off that mount and onto another vfsmount as the path of
the link is walked, thus keeping reference counts proper.

The changes made in fs/namei.c@1.42 break this behaviour if the dentry
being follow_link'ed is a root dentry. This is because follow_mount
follows down next.mnt and not nd->mnt like it used to. So, if a root
dentry has a follow_link op, the nd->mnt it receives is in fact the
vfsmount of the mount it is mounted upon (which breaks reference counts).

Signed-off-by: Mike Waychison <michael.waychison@sun.com>
---

 namei.c |    2 ++
 1 files changed, 2 insertions(+)

Index: linux-2.6.9-quilt/fs/namei.c
===================================================================
--- linux-2.6.9-quilt.orig/fs/namei.c	2004-10-22 17:17:34.762179488 -0400
+++ linux-2.6.9-quilt/fs/namei.c	2004-10-22 17:17:46.571384216 -0400
@@ -755,6 +755,7 @@ int fastcall link_path_walk(const char *
 
 		if (inode->i_op->follow_link) {
 			mntget(next.mnt);
+			nd->mnt = next.mnt;
 			err = do_follow_link(next.dentry, nd);
 			dput(next.dentry);
 			mntput(next.mnt);
@@ -809,6 +810,7 @@ last_component:
 		if ((lookup_flags & LOOKUP_FOLLOW)
 		    && inode && inode->i_op && inode->i_op->follow_link) {
 			mntget(next.mnt);
+			nd->mnt = next.mnt;
 			err = do_follow_link(next.dentry, nd);
 			dput(next.dentry);
 			mntput(next.mnt);