Bug#107826: can not create file through a dangling symlink

[Roland McGrath]

> > > In skimming a couple parts of the spec, I also noticed it now explicitly
> > > says that a lookup of "" must fail.  So we should change this too.
> > Yes.
> Would such a change go in dir-lookup, or in the libc open function?
> Does the requirements of the standard apply to more posix functions or
> just open?

The specification is for all pathname translation--it always works the
same, no matter what particular functions you are using.  In the Hurd
implementation, this all happens in the hurd_file_name_lookup functions
(libc/hurd/hurdlookup.c) or in the dir_lookup RPC server.  I think that all
we need to change right now to match this new spec is to insert a check for
"" in hurd_file_name_lookup and hurd_file_name_split.

> The current behaviour is quite logical given the requirement that
> "foo/////bar" is the same thing as "foo/bar".

We agree.  But everyone else has agreed that "" must fail.