On Sat, 30 Jun 2007 01:51:25 -0400
Andreas Dilger <adilger@xxxxxxxxxxxxx> wrote:
> I don't think there is actually any fundamental difference between these
> proposals. The reality is that we cannot change the semantics of the
> META_BG flag at this point, since both e2fsprogs and ext3/ext4 in the
> kernel understand META_BG to mean only "group descriptor backups are
> in groups {0, 1, last} of the metagroup" and nothing else.
Agree. I call it extended META_BG for lack of a better name, but a new
feature flag will be required.
> If we want to allow the bitmaps and inode table outside the group they
> represent then this needs to be a separate feature flag, and we may as
> well include the additional improvement of the BIG_BG feature at the
> same time. I don't think this really any reason to claim there is "no
> need to have a concept of block groups".
Well when I think about block groups, it seems to me that its basically
a range of blocks with some blocks dedicated for holding important meta
data. If you remove the meta data, then all that is left is a range of
blocks with some backup data scatter around specific locations on the
disk. Of course, my definition of what a block group is could just be
wrong. :)
We could blur the difference between these two features though.
> Also note that e2fsprogs already reserves the bg_free_*_bg fields for
> BIG_BG in the expanded group descriptors, though there is no official
> definition for BIG_BG:
>
> struct ext4_group_desc
> {
> [ ext3_group_desc ]
> __u32 bg_block_bitmap_hi; /* Blocks bitmap block MSB */
> __u32 bg_inode_bitmap_hi; /* Inodes bitmap block MSB */
> __u32 bg_inode_table_hi; /* Inodes table block MSB */
> __u16 bg_free_blocks_count_hi;/* Free blocks count MSB */
> __u16 bg_free_inodes_count_hi;/* Free inodes count MSB */
> __u16 bg_used_dirs_count_hi; /* Directories count MSB */
> __u16 bg_pad;
> __u32 bg_reserved2[3];
> };
>
>
>
> Cheers, Andreas
> --
> Andreas Dilger
> Principal Software Engineer
> Cluster File Systems, Inc.
>
Thanks for the pointer.
-JRS
-
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
