Re: rfc: [patch 3/6] more e2fsprogs fixes

On Aug 25, 2006  15:18 +0200, Alexandre Ratchov wrote:
> add bg_{block_bitmap,inode_bitmap,inode_table}_hi fields in
> struct ext2_group_desc and use absolute block numbers. While
> this is not necessary, IMHO this is simpler than relative
> addressing, and this change make e2fsprogs "just" work.
> 
>  {
> +	__u32	bg_block_bitmap;	/* Blocks bitmap block */
> +	__u32	bg_inode_bitmap;	/* Inodes bitmap block */
>  	__u32	bg_inode_table;		/* Inodes table block */
>  	__u16	bg_free_blocks_count;	/* Free blocks count */
>  	__u16	bg_free_inodes_count;	/* Free inodes count */
>  	__u16	bg_used_dirs_count;	/* Directories count */
>  	__u16	bg_flags;
> +	__u32	bg_block_bitmap_hi;	/* Blocks bitmap block */
> +	__u32	bg_inode_bitmap_hi;	/* Inodes bitmap block */
> +	__u32	bg_inode_table_hi;	/* Inodes table block */
> +	/*__u16	bg_reserved[3];*/

This consumes all of the blockgroup reserved fields, not leaving any
for checksumming.  In particular, for the UNINIT group changes this
needs at least 16 bits for the checksum, and it would be good to have
a 32-bit checksum for the block and inode bitmaps.

Instead, why not put a 16-bit "_block_bitmap_hi" field here and then
the inode bitmap and inode table are relative to that?  Alternately,
if we want a full 32-bit "hi" value, we can maybe live with smaller
checksums on the bitmaps...
 
Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.


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