From owner-freebsd-current  Fri Jun 15 21:36: 7 2001
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Date: Sat, 16 Jun 2001 14:34:07 +1000 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: "Steve O'Hara-Smith" <steveo@eircom.net>
Cc: David Wolfskill <david@catwhisker.org>, current@FreeBSD.ORG
Subject: Re: symlink(2) [Was: Re: tcsh.cat]
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On Fri, 15 Jun 2001, Steve O'Hara-Smith wrote:

> On Fri, 15 Jun 2001 06:31:12 -0700 (PDT)
> David Wolfskill <david@catwhisker.org> wrote:
> 
> DW> Indeed: it is my understanding that the "path name" interpretation is
> DW> an issue at the time of reference, not (necessarily) the time of
> DW> creation.  It has, to the best of my knowledge, been valid to create a
> DW> symlink prior to a point when its target exists.
> 
> 	It has been on evey platform I have ever used ln -s on.
> 
> DW> One may well argue that this is "broken" in some way(s).  Still, changing
> DW> it at this point could well be considered  a POLA violation, at best.
> 
> 	I would argue loud and long that changing that *would* be broken. There
> is never a guarantee (or even an implication) that a symlink points to a
> valid directory entry (think unmounted filesystems, NFS ...). I find it hard
> to imagine why creation time should be special in that regard.

We are (or at least I am) talking about changing it to prevent links to a
string that can _never_ be a valid pathname.  Fortunately, in POSIX there
is only one such string (the empty string).

Here's an example of a standard utility being clueless about symlinks to
nothing:

    $ ln -s '' foo
    $ cp foo bar
    cp: foo is a directory (not copied)

foo is certainly not a directory.  The bug seems to be in fts.

cp is also broken for symlinks to valid pathnames for nonexistent files;

    $ rm -f foo
    $ ln -s /nonesuch foo
    $ cp foo bar

This duplicates foo as a symlink, but should just fail.

Bruce


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