new step_into() flag: WALK_NOFOLLOW

Tells step_into() not to follow symlinks, regardless of LOOKUP_FOLLOW.
Allows to switch handle_lookup_down() to of step_into(), getting
all follow_managed() and step_into() calls paired.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -1827,7 +1827,7 @@ static int pick_link(struct nameidata *nd, struct path *link,
 	return 1;
 }
 
-enum {WALK_FOLLOW = 1, WALK_MORE = 2};
+enum {WALK_FOLLOW = 1, WALK_MORE = 2, WALK_NOFOLLOW = 4};
 
 /*
  * Do we need to follow links? We _really_ want to be able
@@ -1839,7 +1839,8 @@ static inline int step_into(struct nameidata *nd, struct path *path,
 			    int flags, struct inode *inode, unsigned seq)
 {
 	if (likely(!d_is_symlink(path->dentry)) ||
-	   !(flags & WALK_FOLLOW || nd->flags & LOOKUP_FOLLOW)) {
+	   !((flags & WALK_FOLLOW) || (nd->flags & LOOKUP_FOLLOW)) ||
+	   (flags & WALK_NOFOLLOW)) {
 		/* not a symlink or should not follow */
 		path_to_nameidata(path, nd);
 		nd->inode = inode;
@@ -2363,10 +2364,7 @@ static int handle_lookup_down(struct nameidata *nd)
 	err = handle_mounts(nd, nd->path.dentry, &path, &inode, &seq);
 	if (unlikely(err < 0))
 		return err;
-	path_to_nameidata(&path, nd);
-	nd->inode = inode;
-	nd->seq = seq;
-	return 0;
+	return step_into(nd, &path, WALK_NOFOLLOW, inode, seq);
 }
 
 /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */