linux-ext4 - Re: problems with large group descriptors and 64bit

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Date:	Thu, 24 Jun 2010 18:35:16 -0600
From:	Andreas Dilger <andreas.dilger@...cle.com>
To:	Valerie Aurora <vaurora@...hat.com>
Cc:	Eric Sandeen <sandeen@...hat.com>,
	"linux-ext4@...r.kernel.orgdevelopment" <linux-ext4@...r.kernel.org>
Subject: Re: problems with large group descriptors and 64bit


On 2010-06-24, at 11:41 AM, Valerie Aurora <vaurora@...hat.com> wrote:

> On Tue, Jun 22, 2010 at 05:24:34PM -0600, Andreas Dilger wrote:
> 
>> lib/ext2fs/blknum.c assumes 64BIT means ext4_group_desc, not s_desc_size:
>> struct ext2_group_desc *ext2fs_group_desc(ext2_filsys fs,
>>                                          struct opaque_ext2_group_desc *gdp,
>>                                          dgrp_t group)
>> {               
>>        if (fs->super->s_desc_size >= EXT2_MIN_DESC_SIZE_64BIT)
>>                return (struct ext2_group_desc *)
>>                        ((struct ext4_group_desc *) gdp + group);
>>        else
>>                return (struct ext2_group_desc *) gdp + group;
>> }
> 
> I'm not sure I understand.  Are there more than two possible sizes for
> group descriptors?  Or is the existing code correct but you'd like to
> use s_desc_size directly for simplicity?

When the 64BIT flag is set the size kid the group descriptor is given by s_group_desc, which is currently the same as struct ext4_group_desc, but it might be larger in the future. --
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