merging pick_link() with get_link(), part 1

Move restoring LOOKUP_PARENT and zeroing nd->stack.name[0] past
the call of get_link() (nothing _currently_ uses them in there).
That allows to moved the call of may_follow_link() into get_link()
as well, since now the presence of LOOKUP_PARENT distinguishes
the callers from each other (link_path_walk() has it, trailing_symlink()
doesn't).

Preparations for folding trailing_symlink() into callers (lookup_last()
and do_last()) and changing the calling conventions of those.  Next
stage after that will have get_link() call migrate into walk_component(),
then - into step_into().  It's tricky enough to warrant doing that
in stages, unfortunately...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -1115,6 +1115,12 @@ const char *get_link(struct nameidata *nd)
 	int error;
 	const char *res;
 
+	if (!(nd->flags & LOOKUP_PARENT)) {
+		error = may_follow_link(nd);
+		if (unlikely(error))
+			return ERR_PTR(error);
+	}
+
 	if (unlikely(nd->flags & LOOKUP_NO_SYMLINKS))
 		return ERR_PTR(-ELOOP);
 
@@ -2329,13 +2335,9 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
 
 static const char *trailing_symlink(struct nameidata *nd)
 {
-	const char *s;
-	int error = may_follow_link(nd);
-	if (unlikely(error))
-		return ERR_PTR(error);
+	const char *s = get_link(nd);
 	nd->flags |= LOOKUP_PARENT;
 	nd->stack[0].name = NULL;
-	s = get_link(nd);
 	return s ? s : "";
 }