linux-ext4 - Re: [PATCH e2fsprogs] Add ZFS detection to libblkid

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Message-id: <20090406062502.GE3199@webber.adilger.int>
Date:	Mon, 06 Apr 2009 00:25:02 -0600
From:	Andreas Dilger <adilger@....com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	"Ricardo M. Correia" <Ricardo.M.Correia@....com>,
	"Theodore Ts'o" <tytso@....edu>, linux-ext4@...r.kernel.org,
	Karel Zak <kzak@...hat.com>
Subject: Re: [PATCH e2fsprogs] Add ZFS detection to libblkid

On Apr 04, 2009  16:46 -0500, Eric Sandeen wrote:
> Andreas Dilger wrote:
> > On Apr 04, 2009  08:04 -0500, Eric Sandeen wrote:
> >> And from another report, another user's zfs partition:
> >>
> >> # hexdump -C first_400K | grep "0c b1 07 b0 f5 02 00 00"
> >> # hexdump -C first_400K | grep "00 00 02 f5 b0 07 b1 0c"
> >> # hexdump -C first_400K | grep "0c b1 ba 00"
> >> 00015e30  30 e8 ff ff 85 c0 5b 75  48 8b 06 35 0c b1 ba 00
> >>
> >> Should we be looking for 0x00babloc at offset 00015e30?
> > 
> > In probe.c I see the magic (that I've been assuming is correct, because
> > it isn't really that easy to read):
> > 
> >   { "zfs",       8,      0,  8, "\0\0\x02\xf5\xb0\x07\xb1\x0c", probe_zfs },
> >   { "zfs",       8,      0,  8, "\x0c\xb1\x07\xb0\xf5\x02\0\0", probe_zfs },
> >   { "zfs",     264,      0,  8, "\0\0\x02\xf5\xb0\x07\xb1\x0c", probe_zfs },
> >   { "zfs",     264,      0,  8, "\x0c\xb1\x07\xb0\xf5\x02\0\0", probe_zfs },
> 
> Yep and that's different from the patch you originally submitted, Andreas...
> 
> > but looking at this I have no idea what this magic value is supposed
> > to represent, from reading the ondiskformat0822.pdf (ZFS spec) document.
> 
> VDEV_BOOT_MAGIC ...
> 
>   333 /* ZFS boot block */
>   334 #define VDEV_BOOT_MAGIC         0x2f5b007b10cULL
> 
> but I can't find much in that spec about where it's supposed to be, at
> least from a very quick skim.

According to ondiskformat0822.pdf this is supposed to be at an 8kB
offset in each of the 4 per-disk labels, but it isn't clear that this
will be in every ZFS filesystem:

	Section 1.3.2: Boot Block Header

	The boot block header is an 8K structure that is reserved for
	future use. The contents of this block will be described in a
	future appendix of this paper.

so I'd prefer to just stick with the überblock magic, which should
be present in all versions of ZFS.

> I'll let you IBM er... SUN guys sort it out  ;)

I'll defer to Ricardo, he is the ZFS expert.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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