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

Al Viro
2019-07-12T12:56:27Z

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...