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From: John Baldwin <jhb@freebsd.org>
To: freebsd-hackers@freebsd.org
Subject: Re: Loader-kernel interaction
Date: Mon, 22 Oct 2012 10:02:40 -0400
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 (bigwig.baldwin.cx); Mon, 22 Oct 2012 10:37:43 -0400 (EDT)
Cc: Richard Yao <ryao@gentoo.org>, "hackers@FreeBSD.org" <hackers@freebsd.org>
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On Friday, October 19, 2012 7:05:05 pm Richard Yao wrote:
> Dear Everyone,
> 
> I know that the kernel is a BTX client, but I do not understand the
> protocol used by loader to pass sysctl settings and loadable modules to
> the kernel. Is there documentation on this?

The loader passes it's variables as a set of environment variables.
They are stored in a contiguous block of memory after the last kernel
module.  Look at sys/boot/i386/libi386/bootinfo{32,64}.c.  Specifically
look at the bi_load*() routines.

-- 
John Baldwin