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

On Wed, May 24, 2006 at 03:52:13PM -0600, Andreas Dilger wrote:
> 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...
> 

I like the idea of changing descriptor size; perhaps we could allow group
descriptors to have variable size (in an analogous way to the inode variable
size)?

cheers,

-- 
Alexandre


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