Subject: Re: [PATCH v9 05/10] namei: O_BENEATH-style path resolution flags

From: Al Viro <[email-masked]>
Date: Fri, 12 Jul 2019 13:55:52 +0100

On Fri, Jul 12, 2019 at 01:39:24PM +0100, Al Viro wrote:
> On Fri, Jul 12, 2019 at 08:57:45PM +1000, Aleksa Sarai wrote:
> 
> > > > @@ -2350,9 +2400,11 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
> > > >  			s = ERR_PTR(error);
> > > >  		return s;
> > > >  	}
> > > > -	error = dirfd_path_init(nd);
> > > > -	if (unlikely(error))
> > > > -		return ERR_PTR(error);
> > > > +	if (likely(!nd->path.mnt)) {
> > > 
> > > Is that a weird way of saying "if we hadn't already called dirfd_path_init()"?
> > 
> > Yes. I did it to be more consistent with the other "have we got the
> > root" checks elsewhere. Is there another way you'd prefer I do it?
> 
> "Have we got the root" checks are inevitable evil; here you are making the
> control flow in a single function hard to follow.
> 
> I *think* what you are doing is
> 	absolute pathname, no LOOKUP_BENEATH:
> 		set_root
> 		error = nd_jump_root(nd)
> 	else
> 		error = dirfd_path_init(nd)
> 	return unlikely(error) ? ERR_PTR(error) : s;
> which should be a lot easier to follow (not to mention shorter), but I might
> be missing something in all of that.

PS: if that's what's going on, I would be tempted to turn the entire
path_init() part into this:
	if (flags & LOOKUP_BENEATH)
		while (*s == '/')
			s++;
in the very beginning (plus the handling of nd_jump_root() prototype
change, but that belongs with nd_jump_root() change itself, obviously).
Again, I might be missing something here...