linux-ext4 - Re: on disk format: value of bg_inode_table

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Message-ID: <20090129051221.GH8990@mit.edu>
Date:	Thu, 29 Jan 2009 00:12:22 -0500
From:	Theodore Tso <tytso@....edu>
To:	Etienne Lorrain <etienne_lorrain@...oo.fr>
Cc:	Andreas Dilger <adilger@....com>, linux-ext4@...r.kernel.org
Subject: Re: on disk format: value of bg_inode_table_hi?

On Wed, Jan 28, 2009 at 08:47:09PM +0000, Etienne Lorrain wrote:
> > De: Andreas Dilger <adilger@....com>
> > Date: Mercredi 28 Janvier 2009, 18h01
> > On Jan 28, 2009  00:20 +0000, Etienne Lorrain wrote:
> > > I have created an ext4 fs on a 64 Mb USB disk by
> > > "mkfs.ext4 /dev/sdb" on debian lenny (no partition).
> > > When I analyse the filesystem using my own tools, I
> > > seem to read at least some bg_inode_table_hi values which
> > > are not null, on such a very small filesystem.

bg_inode_table_hi doesn't exist on a small filesystem.  You need to
take a look at if INCOMPAT_64BIT is not set, or if INCOMPAT_64BIT is
set and s_desc_size is 32, then only the first 32 bytes of struct
ext4_group_desc are in use --- which look exactly the same as
ext2_group_desc.

So there is no problem here.  Just a misunderstanding of the
filesystem format.

						- Ted
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