linux-ext4 - Re: [PATCH 1/7] ext4: Introduce le32_t and le16

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Date:	Tue, 25 Sep 2007 08:56:09 -0500
From:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	linux-ext4@...r.kernel.org, adilger@...sterfs.com, cmm@...ibm.com
Subject: Re: [PATCH 1/7] ext4: Introduce le32_t and le16_t

On Tue, 2007-09-25 at 14:33 +0530, Aneesh Kumar K.V wrote:
> ext4 file system layout contain different split members
> like bg_block_bitmap  and bg_block_bitmap_hi. Introduce
> data type le32_t and le16_t to be used as the type of
> these split members. This prevents these members frome
> being accessed directly. Accesing them directly gives
> a compiler warning. This helps in catching some BUGS
> due to direct partial access of these split fields.

Ugh.  I don't like this typedef at all. It just makes the data type more
confusing.

Why not just change the name of bg_block_bitmap to something like
bg_block_bitmap_lo or _bg_block_bitmap?  It should be clear from the
name that it shouldn't be used without careful consideration.

> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> ---
>  fs/ext4/super.c           |    8 ++++----
>  include/linux/ext4_fs.h   |    4 ++--
>  include/linux/ext4_fs_i.h |    4 ++++
>  3 files changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index d035653..c8f8e4d 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -70,9 +70,9 @@ static void ext4_write_super_lockfs(struct super_block *sb);
>  ext4_fsblk_t ext4_block_bitmap(struct super_block *sb,
>  			       struct ext4_group_desc *bg)
>  {
> -	return le32_to_cpu(bg->bg_block_bitmap) |
> +	return le32_to_cpu(bg->bg_block_bitmap.value) |
>  		(EXT4_DESC_SIZE(sb) >= EXT4_MIN_DESC_SIZE_64BIT ?
> -		 (ext4_fsblk_t)le32_to_cpu(bg->bg_block_bitmap_hi) << 32 : 0);
> +		 (ext4_fsblk_t)le32_to_cpu(bg->bg_block_bitmap_hi.value) << 32 : 0);
>  }
> 
>  ext4_fsblk_t ext4_inode_bitmap(struct super_block *sb,
> @@ -94,9 +94,9 @@ ext4_fsblk_t ext4_inode_table(struct super_block *sb,
>  void ext4_block_bitmap_set(struct super_block *sb,
>  			   struct ext4_group_desc *bg, ext4_fsblk_t blk)
>  {
> -	bg->bg_block_bitmap = cpu_to_le32((u32)blk);
> +	bg->bg_block_bitmap.value = cpu_to_le32((u32)blk);
>  	if (EXT4_DESC_SIZE(sb) >= EXT4_MIN_DESC_SIZE_64BIT)
> -		bg->bg_block_bitmap_hi = cpu_to_le32(blk >> 32);
> +		bg->bg_block_bitmap_hi.value = cpu_to_le32(blk >> 32);
>  }
> 
>  void ext4_inode_bitmap_set(struct super_block *sb,
> diff --git a/include/linux/ext4_fs.h b/include/linux/ext4_fs.h
> index 046a6a7..4494f8e 100644
> --- a/include/linux/ext4_fs.h
> +++ b/include/linux/ext4_fs.h
> @@ -150,7 +150,7 @@ struct ext4_allocation_request {
>   */
>  struct ext4_group_desc
>  {
> -	__le32	bg_block_bitmap;	/* Blocks bitmap block */
> +	le32_t	bg_block_bitmap;	/* Blocks bitmap block */
>  	__le32	bg_inode_bitmap;	/* Inodes bitmap block */
>  	__le32	bg_inode_table;		/* Inodes table block */
>  	__le16	bg_free_blocks_count;	/* Free blocks count */
> @@ -160,7 +160,7 @@ struct ext4_group_desc
>  	__u32	bg_reserved[2];		/* Likely block/inode bitmap checksum */
>  	__le16  bg_itable_unused;	/* Unused inodes count */
>  	__le16  bg_checksum;		/* crc16(sb_uuid+group+desc) */
> -	__le32	bg_block_bitmap_hi;	/* Blocks bitmap block MSB */
> +	le32_t	bg_block_bitmap_hi;	/* Blocks bitmap block MSB */
>  	__le32	bg_inode_bitmap_hi;	/* Inodes bitmap block MSB */
>  	__le32	bg_inode_table_hi;	/* Inodes table block MSB */
>  };
> diff --git a/include/linux/ext4_fs_i.h b/include/linux/ext4_fs_i.h
> index 22ba80e..d7eb271 100644
> --- a/include/linux/ext4_fs_i.h
> +++ b/include/linux/ext4_fs_i.h
> @@ -27,6 +27,10 @@ typedef int ext4_grpblk_t;
>  /* data type for filesystem-wide blocks number */
>  typedef unsigned long long ext4_fsblk_t;
> 
> +/* data type to carry split 64 and 48 bits */
> +typedef struct { __le16 value; } le16_t;
> +typedef struct { __le32 value; } le32_t;
> +
>  struct ext4_reserve_window {
>  	ext4_fsblk_t	_rsv_start;	/* First byte reserved */
>  	ext4_fsblk_t	_rsv_end;	/* Last byte reserved or 0 */
-- 
David Kleikamp
IBM Linux Technology Center

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