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Date:	Wed, 01 Sep 2010 19:08:43 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Andreas Dilger <adilger.kernel@...ger.ca>
CC:	Justin Maggard <jmaggard10@...il.com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: Broken e2fsck i_blocks repair

Andreas Dilger wrote:
> On 2010-09-01, at 16:01, Justin Maggard wrote:
>> I've mentioned this before on here, but I never verified whether or
>> not it was actually broken.  I have done so today.  I manually
>> modified the block count of a 3TB file using debugfs, then ran e2fsck
>> on it.  e2fsck claimed to repair it, but would throw an error on every
>> subsequent e2fsck run for the same issue.  The reason is
>> inode->osd2.linux2.l_i_blocks_hi is always set to 0 if e2fsck is told
>> to fix it.  This is an issue in both stable 1.41.12, and in master.
>> This patch fixes it for me, but is there anything else that needs to
>> get checked here?
> 
> It probably makes sense to audit all uses of "i_blocks" to see if
> they behave similarly badly w.r.t. l_i_blocks_hi. A casual glance
> indicates that there are a number of places that are similarly
> broken.
> 
> I see there is a helper function
> e2fsck/blknum.c:ext2fs_inode_i_blocks() that should be used for most
> i_blocks accesses (excluding those places in e2fsck that check for
> l_i_blocks_hi being non-zero without the appropriate feature flag
> being set). It might make sense to rename this function
> ext2fs_inode_i_blocks_get() and add similar
> ext2fs_inode_i_blocks_set() routine to set it correctly.

maybe another thing to try to make opaque to make mistakes
impossible...?

-Eric

> 
>> diff -urp e2fsprogs-1.41.12/e2fsck/pass1.c e2fsprogs-1.41.12-jm/e2fsck/pass1.c
>> --- e2fsprogs-1.41.12/e2fsck/pass1.c	2010-05-14 14:51:21.000000000 -0700
>> +++ e2fsprogs-1.41.12-jm/e2fsck/pass1.c	2010-09-01 15:54:42.000000000 -0700
>> @@ -2044,7 +2044,7 @@ static void check_blocks(e2fsck_t ctx, s
>> 		pctx->num = pb.num_blocks;
>> 		if (fix_problem(ctx, PR_1_BAD_I_BLOCKS, pctx)) {
>> 			inode->i_blocks = pb.num_blocks;
>> -			inode->osd2.linux2.l_i_blocks_hi = 0;
>> +			inode->osd2.linux2.l_i_blocks_hi = (pb.num_blocks >> 32);
>> 			dirty_inode++;
>> 		}
>> 		pctx->num = 0;
>>
>> -Justin
>> --
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> 
> 
> Cheers, Andreas
> 
> 
> 
> 
> 
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