Re: [RFC][E2FSPROGS][PATCH 1/8]

On May 24, 2006  16:36 +0200, Alexandre Ratchov wrote:
> move the new 'bg_flags' field of the ext2_group_desc structure in
> order to make room for the MSB of the 64bit fields.

Since the BIG_BG support is a mke2fs-time option (i.e. it is impossible
to convert an existing filesystem to this layout) Laurent and I had
previously discussed changing the ext3_group_desc struct to be 256 bytes
in size in order to more easily accomodate the larger fields.

The reason I'm concerned about using up these fields in the existing
group descriptor is that some other features such as inode and block
bitmap checksums, the group descriptor checksum, and the itable "high
watermark" value (which could be enabled on existing filesystems) all
need space in the existing group descriptor also.

That is at least 4 + 4 + 1 + 2 = 11 bytes, and there are only 7 left
after the BIG_BG changes...

> --- e2fsprogs.orig/lib/ext2fs/ext2_fs.h	2006-05-24 15:22:50.000000000 +0200
> +++ e2fsprogs/lib/ext2fs/ext2_fs.h	2006-05-24 15:25:24.000000000 +0200
> @@ -143,8 +143,10 @@
>  	__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_pad;
> +	__u32	bg_reserved1;
>  	__u16	bg_flags;
> -	__u32	bg_reserved[3];
> +	__u16	bg_reserved2[3];
>  };

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.



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