linux-kernel - Re: [PATCH 1/4] fs: befs: Remove redundant validation from befs_find_brun

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Message-ID: <5777A7AA.4020500@osg.samsung.com>
Date:	Sat, 02 Jul 2016 12:38:18 +0100
From:	Luis de Bethencourt <luisbg@....samsung.com>
To:	Salah Triki <salah.triki@...il.com>, akpm@...ux-foundation.org,
	viro@...iv.linux.org.uk
CC:	mhocko@...e.com, vdavydov@...tuozzo.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] fs: befs: Remove redundant validation from befs_find_brun_direct

On 02/07/16 09:05, Salah Triki wrote:
> The only caller of befs_find_brun_direct is befs_fblock2brun, which
> already validates that the block is within the range of direct blocks.
> So remove the duplicate validation.
> 
> Signed-off-by: Salah Triki <salah.triki@...il.com>
> ---
>  fs/befs/datastream.c | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/fs/befs/datastream.c b/fs/befs/datastream.c
> index 26cc417..e224b9a 100644
> --- a/fs/befs/datastream.c
> +++ b/fs/befs/datastream.c
> @@ -249,17 +249,9 @@ befs_find_brun_direct(struct super_block *sb, const befs_data_stream *data,
>  	int i;
>  	const befs_block_run *array = data->direct;
>  	befs_blocknr_t sum;
> -	befs_blocknr_t max_block =
> -	    data->max_direct_range >> BEFS_SB(sb)->block_shift;
>  
>  	befs_debug(sb, "---> %s, find %lu", __func__, (unsigned long)blockno);
>  
> -	if (blockno > max_block) {
> -		befs_error(sb, "%s passed block outside of direct region",
> -			   __func__);
> -		return BEFS_ERR;
> -	}
> -
>  	for (i = 0, sum = 0; i < BEFS_NUM_DIRECT_BLOCKS;
>  	     sum += array[i].len, i++) {
>  		if (blockno >= sum && blockno < sum + (array[i].len)) {
> 

Hi Salah,

These aren't the same check though. If we ignore the BEFS_SB(sb)->block_shift just to
comparing them, we can consider the checks to be the following.

In befs_fblock2brun():
if (fblock < data->max_direct_range)

In befs_find_brun_direct():
if (fblock > data->max_direct_range)

Notice how one checks if the block is past the range, and the other checks if it isn't
before it.

They also looked similar to me the first time I saw them and I had to double-check :)

Thanks,
Luis