Embed a struct path into struct nameidata instead of nd->{dentry,mnt}

This is the central patch of a cleanup series. In most cases there is no good
reason why someone would want to use a dentry for itself. This series reflects
that fact and embeds a struct path into nameidata.

Together with the other patches of this series
- it enforced the correct order of getting/releasing the reference count on
  <dentry,vfsmount> pairs
- it prepares the VFS for stacking support since it is essential to have a
  struct path in every place where the stack can be traversed
- it reduces the overall code size:

without patch series:
   text    data     bss     dec     hex filename
5321639  858418  715768 6895825  6938d1 vmlinux

with patch series:
   text    data     bss     dec     hex filename
5320026  858418  715768 6894212  693284 vmlinux

This patch:

Switch from nd->{dentry,mnt} to nd->path.{dentry,mnt} everywhere.

[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: fix cifs]
[akpm@linux-foundation.org: fix smack]
Signed-off-by: Jan Blunck <jblunck@suse.de>
Signed-off-by: Andreas Gruenbacher <agruen@suse.de>
Acked-by: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/base.c

@@ -1170,7 +1170,8 @@ static void *proc_pid_follow_link(struct dentry *dentry, struct nameidata *nd)
 	if (!proc_fd_access_allowed(inode))
 		goto out;
 
-	error = PROC_I(inode)->op.proc_get_link(inode, &nd->dentry, &nd->mnt);
+	error = PROC_I(inode)->op.proc_get_link(inode, &nd->path.dentry,
+						&nd->path.mnt);
 	nd->last_type = LAST_BIND;
 out:
 	return ERR_PTR(error);

fs/proc/proc_sysctl.c

@@ -407,7 +407,7 @@ static int proc_sys_permission(struct inode *inode, int mask, struct nameidata *
 	if (!nd || !depth)
 		goto out;
 
-	dentry = nd->dentry;
+	dentry = nd->path.dentry;
 	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
 
 	/* If the entry does not exist deny permission */