Re: [Ext2-devel] ext2 inode size (on-disk)

[Andreas Dilger <adilger@turbolinux.com>]

Al writes:
> I don't think that it's needed - old kernels (up to -CURRENT ;-) will
> simply refuse to mount if ->s_inode_size != 128. Old utilites may be
> trickier, though...

Probably would need an incompat flag for changing the inode size anyways,
so old utilities wouldn't set that anyways.

> I'm somewhat concerned about the following: last block of inode table
> fragment may have less inodes than the rest. Reason: number of inodes
> per group should be a multiple of 8 and with inodes bigger than 128
> bytes it may give such effect. Comments?

I don't _think_ that there is a requirement for a multiple-of-8 inodes
per group.  OK, looking into mke2fs (actually lib/ext2fs/initialize.c)
it _does_ show that it needs to be a multiple of 8, but I'm not sure
exactly what the "bitmap splicing code" mentioned in the comment is.

In the end, it doesn't really matter much - if we go with multiple-of-2
inode sizes, all it means is that we may need to have multiple-of-2 (or
possibly 4 for 512-byte inodes in a 1k block filesystem) inode table
blocks in each group.  Not a big deal.  The code already handles this.

> I would really, really like to end up with accurate description of
> inode table layout somewhere in Documentation/filesystems. Heck, I
> volunteer to write it down and submit into the tree ;-)

I can write a few words as well.

Cheers, Andreas
-- 
Andreas Dilger  \ "If a man ate a pound of pasta and a pound of antipasto,
                 \  would they cancel out, leaving him still hungry?"
http://www-mddsp.enel.ucalgary.ca/People/adilger/               -- Dogbert