linux-kernel - Re: BTRFS partition usage...

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20080213004541.GB11911@mit.edu>
Date:	Tue, 12 Feb 2008 19:45:41 -0500
From:	Theodore Tso <tytso@....EDU>
To:	David Miller <davem@...emloft.net>
Cc:	jengelh@...putergmbh.de, chris.mason@...cle.com,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	btrfs-devel@....oracle.com
Subject: Re: BTRFS partition usage...

On Tue, Feb 12, 2008 at 03:28:26PM -0800, David Miller wrote:
> From: Jan Engelhardt <jengelh@...putergmbh.de>
> Date: Tue, 12 Feb 2008 15:00:20 +0100 (CET)
> 
> > Something looks wrong here. Why would btrfs need to zero at all?
> 
> So that existing superblocks on the partition won't
> be interpreted as correct by other filesystems.  It's
> a safety measure many mkfs programs use.
> 
> > Superblock at 0, and done. Just like xfs.
> 
> No, we won't do stupid things like that and make an entire
> cylinder of our disks unusable.  See my other reply.

The reason why we don't put the superblock at 0 is not because it
screws over the sparc, but because on many systems (including x86) the
bootsector is stored at 0.  It's not hard for mke2fs to zap the boot
sector which we do on all architectures *except* sparc, to avoid
nuking the disk label.  (Chris just missed the "#ifndef __sparc //
#define ZAP_BOOTBLOCK // #endif" at the beginning of mke2fs.c)

This is the best of all words; it makes sparc happy; it allows boot
loaders to put the x86 standard initial stage 0 boot loader in the
first 446 bytes of the disk; and by zapping sector 0 on all
architectures except the sparc, it solves the previous filesystem
"ghost traces" detection problem for filesystems like xfs that put the
superblock at 0.

						- Ted
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/