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>

arch/um/drivers/mconsole_kern.c

@@ -145,8 +145,8 @@ void mconsole_proc(struct mc_request *req)
 	}
 	up_write(&super->s_umount);
 
-	nd.dentry = super->s_root;
-	nd.mnt = NULL;
+	nd.path.dentry = super->s_root;
+	nd.path.mnt = NULL;
 	nd.flags = O_RDONLY + 1;
 	nd.last_type = LAST_ROOT;
 
@@ -159,7 +159,7 @@ void mconsole_proc(struct mc_request *req)
 		goto out_kill;
 	}
 
-	file = dentry_open(nd.dentry, nd.mnt, O_RDONLY);
+	file = dentry_open(nd.path.dentry, nd.path.mnt, O_RDONLY);
 	if (IS_ERR(file)) {
 		mconsole_reply(req, "Failed to open file", 1, 0);
 		goto out_kill;