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From: ed@mtxinu.UUCP (Ed Gould)
Newsgroups: comp.unix.wizards
Subject: Re: Symbolic Links
Message-ID: <480@mtxinu.UUCP>
Date: Wed, 31-Dec-69 18:59:59 EDT
Article-I.D.: mtxinu.480
Posted: Wed Dec 31 18:59:59 1969
Date-Received: Thu, 27-Aug-87 07:21:05 EDT
References: <8731@brl-adm.ARPA> <2789@ulysses.homer.nj.att.com> <1781@munnari.oz> <2838@ulysses.homer.nj.att.com> <1793@munnari.oz> <2854@ulysses.homer.nj.att.com>
Reply-To: ed@mtxinu.UUCP (Ed Gould)
Organization: mt Xinu, Berkeley
Lines: 59

>This argument, that ".." is a physical link (rather than a logical one)
>falls appart at mount points, where the parent directory and where ".." points
>are different. It also happens at remote file system mount points, for
>the same reason. So it's not so "simple and consistent". It now requires
>some education about file systems, mount points, and distributed file
>systems. The list seems to keep growing.

It doesn't fall apart anywhere on my system (4.3BSD + NFS) except that
/ is a special case: /.. == /

>This is easy. The intention is to make ".." behave as a logical operator.
>This means that
>
>1: if I do "cd /usr/include/sys" and then "cd ..", I end up in /usr/include
>   no matter what.
>
>2: if I find a ".." in a pathname, it refers to the logical parent,
>   not the physical one. Thus, while in /usr/include/sys, "ls .." will produce
>   a directory listing of /usr/include.
>
>The semantics are very clean and simple.

Simple, perhaps, but no more so than the current BSD symlinks.  What's
cleaner about it?

>You can't achieve 2: above unless it's done in the kernel.

No argument.

>An implementation is not only possible, it already exists. I wouldn't be
>defending this if I didn't have the opportunity to use it and test it and
>get the feeling as to whether it's the right thing to do or not.

Unless the kernel implements carrying an arbitrarily-long string with
each process, then I claim that the implementation is broken.  Consider
the following program, with DEPTH suitably large:

	main() {
		int i;

		for(i = 0; i < DEPTH; i++) {
			mkdir("subdir");
			symlink("subdir", "symlink");
			chdir("symlink");
		}
		chdir("../../..");
		/* 
		 * Where am I now and how did I get there???
		 */
	}

(This example could be improved, but I believe that it illustrates
my point.)

-- 
Ed Gould                    mt Xinu, 2560 Ninth St., Berkeley, CA  94710  USA
{ucbvax,decvax}!mtxinu!ed   +1 415 644 0146

"A man of quality is not threatened by a woman of equal022ran