Subject: Re: [Ext2-devel] [PATCH] fix ext3 mounts at 16T
From: Mingming Cao <cmm@us.ibm.com>
Reply-To: cmm@us.ibm.com
To: Eric Sandeen <esandeen@redhat.com>
Cc: ext2-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org
In-Reply-To: <44DD00FA.5060600@redhat.com>
References: <44DD00FA.5060600@redhat.com>
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Organization: IBM LTC
Date: Fri, 11 Aug 2006 15:29:54 -0700
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On Fri, 2006-08-11 at 17:13 -0500, Eric Sandeen wrote:
> I figure before we get too fired up about 48 bits and ext4 let's fix 32 bits on ext3 :)
> 
> I need to do some actual IO testing now, but this gets things mounting for a 16T ext3 filesystem.
> (patched up e2fsprogs is needed too, I'll send that off the kernel list)
> 
> This patch fixes these issues in the kernel:
> 
> o sbi->s_groups_count overflows in ext3_fill_super()
> 
> 	sbi->s_groups_count = (le32_to_cpu(es->s_blocks_count) -
> 			       le32_to_cpu(es->s_first_data_block) +
> 			       EXT3_BLOCKS_PER_GROUP(sb) - 1) /
> 			      EXT3_BLOCKS_PER_GROUP(sb);
> 
> at 16T, s_blocks_count is already maxed out; adding EXT3_BLOCKS_PER_GROUP(sb) overflows it and 
> groups_count comes out to 0.  Not really what we want, and causes a failed mount.
> 
> Feel free to check my math (actually, please do!), but changing it this way should work & 
> avoid the overflow:
> 
> (A + B - 1)/B changed to: ((A - 1)/B) + 1
> 
> o ext3_check_descriptors() overflows range checks

Looks correct to me.:)

Mingming

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