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From: Robert Watson <rwatson@FreeBSD.org>
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To: Ed Schouten <ed@80386.nl>
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Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject: Re: cvs commit: src ObsoleteFiles.inc src/libexec Makefile
 src/libexec/pt_chown Makefile pt_chown.c
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On Sun, 24 Aug 2008, Ed Schouten wrote:

> There is no need for compat libraries, because the existing ones already do 
> this:
>
> - Try to run pt_chown.
> - If that fails, try to chmod/chown the slave device by hand.
> - If that fails, return an error.
>
> Because the PTY that openpty() obtains already has the proper permissions in 
> place, the second step won't fail.

Sounds good.  The two compat cases I have in mind are:

(1) Pure system call ABI: do old libraries, binaries, and synchronized
     configuration files work with the new kernel.  The "in a jail" case.

(2) Mixed ABI: do old libraries and binaries work with new configuration
     files, new binaries, and new kernels.

On the whole we don't get too many cases of problems with (2), since many 
config files have fairly static content and syntax over time.  The two recent 
cases where I've seen problems have been old libc malloc's with new 
malloc.conf's (lots of warnings, but works fine as far as I can tell), and 
with /etc/ttys.

Robert N M Watson
Computer Laboratory
University of Cambridge