linux-ext4 - Re: [PATCH 2/2][64-BIT] ext2fs_group_first

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Date:	Sat, 18 Apr 2009 08:09:43 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	nicholas.dokos@...com
CC:	linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>,
	Valerie Aurora <vaurora@...hat.com>
Subject: Re: [PATCH 2/2][64-BIT] ext2fs_group_first_block2(): 32-bit truncation.

Nick Dokos wrote:
> ext2fs_group_first_block2() returns the product of the group number
> and the number of blocks per group (from the superblock). Unfortunately,
> both of these are 32-bit quantities, so the multiplication result is
> also 32 bits wide. It is then returned as a 64-bit quantity, but by then,
> it's too late.
> 
> Cast one of the operands to blk64_t, so the multiplication will be done
> in 64 bits.
> 
> e2fsck was complaining about a group that was marked BLOCK_UNINIT, but
> had blocks in use (it turned out that a different group had blocks in
> use, but the block numbers of the two different groups differed by
> 2^32, so this bug conflated them). With this change, this complaint
> goes away. In addition, dumpe2fs produces the right blocks for all the
> groups, whereas it was wrapping them at the 32-bit boundary previously.
> 
> Signed-off-by: Nick Dokos <nicholas.dokos@...com>

This one looks obviously correct, thanks.

Reviewed-by: Eric Sandeen <sandeen@...hat.com>

> ---
>  lib/ext2fs/blknum.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/lib/ext2fs/blknum.c b/lib/ext2fs/blknum.c
> index b9666fb..fd56d53 100644
> --- a/lib/ext2fs/blknum.c
> +++ b/lib/ext2fs/blknum.c
> @@ -28,7 +28,7 @@ dgrp_t ext2fs_group_of_blk2(ext2_filsys fs, blk64_t blk)
>  blk64_t ext2fs_group_first_block2(ext2_filsys fs, dgrp_t group)
>  {
>  	return fs->super->s_first_data_block +
> -		(group * fs->super->s_blocks_per_group);
> +		((blk64_t)group * fs->super->s_blocks_per_group);
>  }
>  
>  /*

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