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Date:      Wed, 4 Aug 1999 09:52:25 +0100 (BST)
From:      Doug Rabson <dfr@nlsystems.com>
To:        "Brian F. Feldman" <green@freebsd.org>
Cc:        Mike Smith <mike@smith.net.au>, Matthew Dillon <dillon@apollo.backplane.com>, Ollivier Robert <roberto@keltia.freenix.fr>, hackers@freebsd.org
Subject:   Re: Jail syscalls 
Message-ID:  <Pine.BSF.4.10.9908040949300.385-100000@salmon.nlsystems.com>
In-Reply-To: <Pine.BSF.4.10.9908040319040.47190-100000@janus.syracuse.net>

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On Wed, 4 Aug 1999, Brian F. Feldman wrote:

> On Tue, 3 Aug 1999, Mike Smith wrote:
> 
> > >     Speaking of the jail() syscall -- it really needs to be revamped a 
> > >     little before people really start using it wholeheartedly.  The size
> > >     of the jail structure needs to be passed in the syscall to allow backwards
> > >     compatibility when things change such as, for example, the size of the
> > >     IP address.
> > 
> > Actually, with interfaces like this you should generally pass a pointer 
> > to the structure in userspace, and stick a version number constant in 
> > the beginning of the structure.  The size is often not enough of a 
> > determining factor...
> 
> Actually, the structure shouldn't change size because it should be
> using a sockaddr.

The argument for versioning is not simply because the size of ip_number
might change (it should be a sockaddr) but because other fields might be
added or removed. To avoid allocating a new syscall whenever this happens,
the structure should be versioned.

Putting sizeof(whatever) at the beginning of the structure works
surprisingly well as a versioning system.

--
Doug Rabson				Mail:  dfr@nlsystems.com
Nonlinear Systems Ltd.			Phone: +44 181 442 9037




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