Re: [Ext2-devel] [RFC] [PATCH 3/4] Add extended attributes to ext 2/3

[Christoph Hellwig <hch@infradead.org>]

On Wed, Oct 09, 2002 at 10:53:47AM +0200, Luka Renko wrote:
> Actually we are currently developing HSM application that stacks on top of
> standard file system (ext3 and XFS today) and we are using EA to store HSM
> specific information with each inode. However, we are not using registration
> API, but rather store this in user EA (even if we don't like some
> limitations of user EA), because registration API is not exported and
> registration API is per-FS and not generic. This would mean that we would
> need to have handlers defined for each supported filesystem (ext3 and XFS
> today, reiserfs and JFS in near future). As we use user EA, we just call VFS
> EA operations of the bottom FS (ext3 or XFS or any other FS that supports
> EA).

Yupp, that's exactly what I meant.

> I think that we could also then have only single ACL code for both ext2 and
> ext3 - currently ACL patch adds similar (same?) code to both ext2 and ext3
> and this code could be shared for sure.

And JFS and reiserfs.  Yes, this code should be in a library, but e.g.
XFS (different ondisk format) or NFSv4/NTFS/whatever need very different
ACL rountines.  You can't easily plug the handler into different filesystems
due to very different implementations below the VFS level.

BTW, do you have a pointer to your DSM system?  I'l like to look at something
less broken them dmapi..