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From: Darren Reed <avalon@coombs.anu.edu.au>
Subject: Re: detecting kernel version at compile time
To: terry@lambert.org (Terry Lambert)
Date: Sat, 12 Apr 1997 12:37:31 +1000 (EST)
Cc: hackers@freebsd.org
In-Reply-To: <199704110018.RAA10243@phaeton.artisoft.com> from "Terry Lambert" at Apr 10, 97 05:18:14 pm
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In some mail from Terry Lambert, sie said:
> 
> > Lets see...firstly, there is <osreldate.h> which is particular to FreeBSD.
> > Including that file always requires #ifdef's for FreeBSD.  Now you want
> > to introduce <sys/osreldate.h>.  That is going to be conditional on what
> > is in <osreldate.h>.  THen code which currently checks for __FreeBSD_version
> > must be adapted to see if __FreeBSD_sysversion exists.
> 
> 1)	<sys/xxx.h> files can *never* depend on <xxx.h> files.

> 2)	You only have to check the version if you want to protect
> 	against a crash better than you currently do.

> > Why weren't __FreeBSD_version & __FreeBSD_sysversion (IF you need both) put
> > in <sys/param.h> ?  For starters, one doesn't need to worry about extra
> > include files, although removing <osreldate.h> would not be good, now.
> 
> I don't know; I've never used <osreldate.h>.  It really only applies
> to the installation insteance of the toolset, and the instances of the
> API enacted by the standard (not system) include files, IMO.
> 
> It seems to me that it's a concession to vendors who don't want to check
> the BSD manifest constants across BSD platforms.

Given this, are there any objections from anyone about putting
__FreeBSD_sysversion in <sys/param.h> ?

As for the BSD symbols, I use them wherever possible.

> You can't possibly have a system component that reference <osreldate.h>,
> since it's not accessable in the kernel build environment (this is the
> problem he is talking about addressing).

Hmmm, can __FreeBSD_sysversion be made the same value as __FreeBSD_version ?
(or vice versa)

> > Further still, there is the uselessness of __FreeBSD__ in some
> > circumstances.
> 
> That would be those vendor circumstances where vendors want all BSD's
> to standardize on the same interfaces.

The problem with __FreeBSD__ is that it is defined by cc - or gcc/pgcc.

That is, it depends on what system the compiler is built, not what OS
it is running on.

Problem being, it impacts every compilation thereafter.