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

On May 29, 2006  17:13 +0200, Alexandre Ratchov wrote:
> 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)?

Sure - have a superblock field which indicates the descriptor size, given
that this is already an incompatible format-time change.  That's a great
idea.

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



-------------------------------------------------------
All the advantages of Linux Managed Hosting--Without the Cost and Risk!
Fully trained technicians. The highest number of Red Hat certifications in
the hosting industry. Fanatical Support. Click to learn more
http://sel.as-us.falkag.net/sel?cmd=lnk&kid=107521&bid=248729&dat=121642