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From: Robert Watson <rwatson@FreeBSD.org>
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To: Matt Sealey <matt@genesi-usa.com>
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Cc: freebsd-fs@freebsd.org
Subject: Re: On-disk format of UFS/UFS2 (for firmware implementation)
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On Tue, 20 Jun 2006, Matt Sealey wrote:

> I was wondering if there is any definitive, authoritative or even just 
> comprehensive documentation on the on-disk format (superblock, nodes, file 
> linking, extents..) of the UFS and UFS2 filesystems.
>
> We would like to implement it in firmware for booting FreeBSD (and NetBSD 
> and eventually Solaris which uses some variant). I have the source code from 
> sys/fs/ufs already but it is not the preferred method of implementing 
> filesystem code. It only needs read support for now so it shouldn't be that 
> complicated, but...

This isn't quite what you're asking for, but you might take a look at 
src/sys/boot/common/ufsread.c, which is used by the FreeBSD boot loader to 
load files from UFS.  It uses include files from sys/ufs.

Robert N M Watson
Computer Laboratory
University of Cambridge