From mboxrd@z Thu Jan  1 00:00:00 1970
From: Lucio De Re <lucio@proxima.alt.za>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] mv vs cp
Message-ID: <20011008062832.V28720@cackle.proxima.alt.za>
References: <20011007162401.77DEE1998A@mail.cse.psu.edu>
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In-Reply-To: <20011007162401.77DEE1998A@mail.cse.psu.edu>; from jmk@plan9.bell-labs.com on Sun, Oct 07, 2001 at 12:23:59PM -0400
Date: Mon,  8 Oct 2001 06:28:32 +0200
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On Sun, Oct 07, 2001 at 12:23:59PM -0400, jmk@plan9.bell-labs.com wrote:
> 
> As Dave points out, there are a lot of balls in the air during
> an atomic 'rename'. 4.2BSD introduced the 'rename' system call,
> and as an alpha/beta tester for 4.1[abc] and 4.2BSD I can testify
> to how long it took to get it right and how much ugly code was
> involved.
> 
There are really only two social factors overriding here.  People
like me have grown to expect it, unfortunate as it may be, and the
alternative is inconsistent and open to error, besides being much
more time and resource intensive.

In addition, it may be more consistent for mv not to go part way
and do a cp+rm on my behalf _on_condition_ that the request is not
recursive, rather not do it at all.  But I suppose my MSDOS background
shows here, the "mv" I'm thinking of is "REN".  That, I ought to
be able to fix by crippling "mv".

What wasn't clear from Dave's response, is whether we would need
a "Tmv" to do it all, including recursive copies that (shudder!)
may need to understand the entire namespace, or just "Tren" that
may still change the namespace, but at least won't have to make
decisions on how to follow mounted resources.

I should imagine that BSD "rename" must have been made orders of
magnitude more complex by symbolic links.  After all, SysV 3.2 "mv"
could rename directories into other directories in the same
filesystem, couldn't it?  It's been a long time since my 3B2 was
turned off, so it's hard for me to check.  I'm almost certain SCO
Xenix and Unix could do it without copying.

++L