linux-kernel - Re: [PATCH] md: remove redudent code

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Message-ID: <20120515180349.0f0d275e@notabene.brown>
Date:	Tue, 15 May 2012 18:03:49 +1000
From:	NeilBrown <neilb@...e.de>
To:	Yuanhan Liu <yuanhan.liu@...ux.intel.com>
Cc:	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] md: remove redudent code

On Tue, 15 May 2012 16:00:25 +0800 Yuanhan Liu <yuanhan.liu@...ux.intel.com>
wrote:

> The code does nothing but repating assigning sb->sb_csum with original
> value.

This code sets the sb_csum to 0 while the csum is calculated.

Without this, calculating the csum, setting it, then calculating again would
produce a different result.

So the code is correct as is.

Thanks,
NeilBrown


> 
> Signed-off-by: Yuanhan Liu <yuanhan.liu@...ux.intel.com>
> ---
>  drivers/md/md.c |    4 ----
>  1 files changed, 0 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 0bd44e3..f2d799a 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -1439,15 +1439,12 @@ super_90_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
>  
>  static __le32 calc_sb_1_csum(struct mdp_superblock_1 * sb)
>  {
> -	__le32 disk_csum;
>  	u32 csum;
>  	unsigned long long newcsum;
>  	int size = 256 + le32_to_cpu(sb->max_dev)*2;
>  	__le32 *isuper = (__le32*)sb;
>  	int i;
>  
> -	disk_csum = sb->sb_csum;
> -	sb->sb_csum = 0;
>  	newcsum = 0;
>  	for (i=0; size>=4; size -= 4 )
>  		newcsum += le32_to_cpu(*isuper++);
> @@ -1456,7 +1453,6 @@ static __le32 calc_sb_1_csum(struct mdp_superblock_1 * sb)
>  		newcsum += le16_to_cpu(*(__le16*) isuper);
>  
>  	csum = (newcsum & 0xffffffff) + (newcsum >> 32);
> -	sb->sb_csum = disk_csum;
>  	return cpu_to_le32(csum);
>  }
>  


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