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From: mwp@munnari.oz (Michael W. Paddon)
Newsgroups: comp.unix.wizards
Subject: Re: Symbolic Links
Message-ID: <1809@munnari.oz>
Date: Thu, 3-Sep-87 02:55:50 EDT
Article-I.D.: munnari.1809
Posted: Thu Sep  3 02:55:50 1987
Date-Received: Sat, 5-Sep-87 10:16:10 EDT
References: <1254@mhres.mh.nl>
Organization: Comp Sci, Melbourne Uni, Australia
Lines: 58

in article <1254@mhres.mh.nl>, jv@mhres.mh.nl (Johan Vromans) says:
> 
> At any moment, I can issue the command "pwd" which gives me the
> current directory. If I am at "/usr/include/sys" then I can deduce what
> my parent is by removing the last element of the name of the current
> directory (in the above example: "/usr/include"). Sounds consistent
> and easy to me.
> 
> Imagine, my system (HP9000/530 with HP-UX, a very good System V.2 with
> Berkeley enhancements) does not have "." and "..":
> 
> %ls -al
> total 158
> -rw-------   1 jv       bsp          422 Apr  1 19:41 .login
> -rw-rw-rw-   1 jv       bsp          263 Sep  1 13:32 .newsrc
> -rw-rw-rw-   1 jv       bsp            0 Sep  1 13:36 .pnewsexpert
> -rw-rw-rw-   1 jv       bsp           26 Sep  1 13:31 .rnlast
> -rw-rw-rw-   1 jv       bsp           58 Aug 27 09:49 .rnsoft
> -rw-r--r--   1 jv       bsp           14 May 23 23:04 .signature
> drwxrwxrwx   1 jv       bsp            0 Aug 18 09:39 News
> drwxr-xr-x   1 jv       bsp          504 Jun 13 01:05 icon
> drwxr-xr-x   1 jv       bsp          912 Sep  1 13:31 maildir
> %
> 
> No dot, no dot-dot, and directories have only one link ... Of course, you
> can access "." and ".." from system calls - it will do what you expect.
> 
> -- 
> Johan Vromans                           | jv@mh.nl via European backbone
> Multihouse N.V., Gouda, the Netherlands | uucp: ..{seismo!}mcvax!mh.nl!jv

I hope you are not suggesting that we don't need '.' and '..' for the
above reasons. The routine getwd(3) [and thereby pwd] use the '..' link
to trace their way back to the root of the tree to yield the true name
of the current directory. The argument for using pwd to obviate the need
for '..' is therefore rather circular.

Note that there is no easy way to find the *real* path of a file or
directory if some of the proposed changes to symbolic links are
implemented in the kernel.
The kernel only knows, in this case, one possible path -- the
one you used to get there. Given this problem, how would you know if
you were removing the real directory or just a symbolic link? As has
been stated before, the solution is to regard symlinks as seperate
objects with their own semantics.

The '.' link is just as useful when a user wants to run an executable
in the current directory instead of the first instance of that name in
his PATH envariable. The only other solution -- putting '.' first in the
path -- is an obvious security risk.


						mwp
						===
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