linux-ext4 - Re: [PATCH 2/2] ext4: fix cpu_vs

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Message-ID: <20130403153742.GA14991@thunk.org>
Date:	Wed, 3 Apr 2013 11:37:42 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	linux-ext4@...r.kernel.org, wenqing.lz@...bao.com
Subject: Re: [PATCH 2/2] ext4: fix cpu_vs_disk conversions

On Wed, Apr 03, 2013 at 02:58:31PM +0400, Dmitry Monakhov wrote:
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index 3a120b2..34da740 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -123,16 +123,15 @@ static __le32 ext4_xattr_block_csum(struct inode *inode,
>  {
>  	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
>  	__u32 csum, old;
> -
> -	old = hdr->h_checksum;
> +	__le64 dsk_block_nr = cpu_to_le64(block_nr);
> +	old = le32_to_cpu(hdr->h_checksum);

We're just saving and restoring hdr->h_checksum.  So instead of
byte-swapping the checksum in old, and then swapping it back, why not
just do this instead:

     __le32 old;

     old = hdr->h_checksum;
     ...
     hdr->h_checksum = old;

					- Ted
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