linux-ext4 - Re: [PATCH 08/31] libext2fs: Fix off-by-one error in file truncation

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Date:	Mon, 7 Oct 2013 16:02:05 +0200 (CEST)
From:	Lukáš Czerner <lczerner@...hat.com>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
cc:	tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 08/31] libext2fs: Fix off-by-one error in file
 truncation

On Mon, 30 Sep 2013, Darrick J. Wong wrote:

> Date: Mon, 30 Sep 2013 18:27:34 -0700
> From: Darrick J. Wong <darrick.wong@...cle.com>
> To: tytso@....edu, darrick.wong@...cle.com
> Cc: linux-ext4@...r.kernel.org
> Subject: [PATCH 08/31] libext2fs: Fix off-by-one error in file truncation
> 
> When told to truncate a file, ext2fs_file_set_size2 should start with the first
> block past the end of the file.  The current calculation jumps one more block
> ahead, with the result that it fails to hack off the last block.  Adding
> blocksize-1 and dividing is sufficient to find the last block.

Looks good.

Reviewed-by: Lukas Czerner <lczerner@...hat.com>

> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> ---
>  lib/ext2fs/fileio.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> 
> diff --git a/lib/ext2fs/fileio.c b/lib/ext2fs/fileio.c
> index ae5cbf1..d875630 100644
> --- a/lib/ext2fs/fileio.c
> +++ b/lib/ext2fs/fileio.c
> @@ -384,10 +384,10 @@ errcode_t ext2fs_file_set_size2(ext2_file_t file, ext2_off64_t size)
>  	EXT2_CHECK_MAGIC(file, EXT2_ET_MAGIC_EXT2_FILE);
>  
>  	truncate_block = ((size + file->fs->blocksize - 1) >>
> -			  EXT2_BLOCK_SIZE_BITS(file->fs->super)) + 1;
> +			  EXT2_BLOCK_SIZE_BITS(file->fs->super));
>  	old_size = EXT2_I_SIZE(&file->inode);
>  	old_truncate = ((old_size + file->fs->blocksize - 1) >>
> -		      EXT2_BLOCK_SIZE_BITS(file->fs->super)) + 1;
> +		      EXT2_BLOCK_SIZE_BITS(file->fs->super));
>  
>  	/* If we're writing a large file, set the large_file flag */
>  	if (LINUX_S_ISREG(file->inode.i_mode) &&
> 
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