linux-ext4 - Re: ext4 compat flag assignments

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Message-ID: <20061005001906.GN22010@schatzie.adilger.int>
Date:	Wed, 4 Oct 2006 18:19:06 -0600
From:	Andreas Dilger <adilger@...sterfs.com>
To:	Theodore Tso <tytso@....edu>
Cc:	Alexandre Ratchov <alexandre.ratchov@...l.net>,
	linux-ext4@...r.kernel.org
Subject: Re: ext4 compat flag assignments

On Oct 04, 2006  16:04 -0400, Theodore Tso wrote:
> On Thu, Sep 28, 2006 at 10:55:15AM +0200, Alexandre Ratchov wrote:
> > struct ext4_super_block
> > {
> > 	/* at offset 0xfe */
> > 	__le32	s_desc_size;		/* Group descriptor size */
> > 	/* at offset 0x150 */
> > 	__le32	s_blocks_count_hi;	/* Blocks count */
> > 	__le32	s_r_blocks_count_hi;	/* Reserved blocks count */
> > 	__le32	s_free_blocks_count_hi;	/* Free blocks count */
> > 	__le32	s_jnl_blocks_hi[17];	/* Backup of the journal inode */
> > };
> 
> Why do we need to have the high blocks # of the journal inode.
> s_jnl_blocks was just a backup of the i_blocks[] array.  But if we are
> assuming that we will only support 64-bits using extents, we shouldn't
> need s_jnl_blocks_hi[].  How specifically is this array being used in
> the patches?

Good question, I don't know that it is.  Even if the journal was extent
mapped (possible, but would need support in e2fsprogs for this) the
data would be stored in the same sized i_blocks array.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.

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