Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hpfcso!hpfcmgw!rdg
From: rdg@hpfcmgw.HP.COM (Rob Gardner)
Newsgroups: comp.sys.hp
Subject: Re: pwd
Message-ID: <1080108@hpfcmgw.HP.COM>
Date: 21 Dec 89 22:27:18 GMT
References: <263@zircon.UUCP>
Organization: HP Fort Collins, CO
Lines: 26


> How does /bin/pwd work?  There is no kernel call to find your current
> directory in UNIX, so it has to do some backhanded peeking in memory
> somewhere, probably in kernel memory.  This suspicion is reinforced by
> /bin/pwd being setuid to root on my system (HP-UX, System V
> compatible).

That's not how it currently works. The actual method is pretty
disgusting, but here's a brief explanation of how it does it:
Open your parent directory (..) and read entries until you find
one whose inode matches the inode of your current directory (.).
Now you know the (base)name of your current directory. Now
you chdir(".."), and repeat to find out the basename of the
parent. You keep doing this until you get to /, and build
up the pathname as you go. This is, of course, a very simplistic
explanation, since there are cases that require special handling.

I think that there will be a kernel call in a "future" release.

 
    Rob Gardner                     hplabs!hpfcmr!rdg
    Hewlett Packard                 or rdg%hpfcmr@hplabs.hp.com
    Fort Collins, Colorado          303-229-2048
		80525-9599

		     "Ask me about Home Brewing"