Re: [PATCH v9 04/10] namei: split out nd->dfd handling to dirfd_path_init

[Al Viro <viro@xxxxxxxxxxxxxxxxxx>]

On Sun, Jul 07, 2019 at 12:57:31AM +1000, Aleksa Sarai wrote:
> Previously, path_init's handling of *at(dfd, ...) was only done once,
> but with LOOKUP_BENEATH (and LOOKUP_IN_ROOT) we have to parse the
> initial nd->path at different times (before or after absolute path
> handling) depending on whether we have been asked to scope resolution
> within a root.

>  	if (*s == '/') {
> -		set_root(nd);
> -		if (likely(!nd_jump_root(nd)))
> -			return s;
> -		return ERR_PTR(-ECHILD);

> +		if (likely(!nd->root.mnt))
> +			set_root(nd);

How can we get there with non-NULL nd->root.mnt, when LOOKUP_ROOT case
has been already handled by that point?

> +		error = nd_jump_root(nd);
> +		if (unlikely(error))
> +			s = ERR_PTR(error);