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To: Marcel Moolenaar <xcllnt@mac.com>
In-reply-to: Your message of "Mon, 23 Aug 2010 16:43:15 PDT."
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Comments: In-reply-to Marcel Moolenaar <xcllnt@mac.com>
	message dated "Mon, 23 Aug 2010 16:43:15 -0700."
Date: Mon, 23 Aug 2010 17:23:49 -0700
From: Bakul Shah <bakul@bitblocks.com>
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Cc: "freebsd-arch@FreeBSD.org" <freebsd-arch@FreeBSD.org>
Subject: Re: RFC: enhancing the root mount logic 
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On Mon, 23 Aug 2010 16:43:15 PDT Marcel Moolenaar <xcllnt@mac.com>  wrote:
> 
> On Aug 23, 2010, at 4:12 PM, M. Warner Losh wrote:
> 
> *snip*
> 
> > However, all this scripting sounds a bit like a very simple shell in
> > the kernel.  What advantages are there to this approach vs having the
> > ability to run a simple shell script or executable and "pivot" the root
> > to a new location?
> 
> The 2 reasons for doing this in the kernel are:
> 1.  resiliency against ABI changes.
> 2.  allowing /sbin/init to come from the actual root file system.
> 
> Both points are impossible to handle efficiently or correctly if
> you need user space support in getting to your actual root file
> system. You basically have a catch-22 or bootstrap problem, which
> a pure in-kernel solution doesn't have.

How about just bundling a small compressed ramfs with the
kernel.  The kernel unpacks it, uses it as the initial rootfs
and runs init from it. A forth/scheme/lua based program
wouldn't add more than a % or so (given that the GENERIC
kernel is over 10MB now!).