At UDS we return to the subject of those drivers we are carrying which are specific to Ubuntu, why they are not yet upstream and what we can do about it. Union Filesystems are a key technology in producing the live CD environment used to allow both non-destructive testing and the graphical installer. This technology has long been a contentious subject as the patch sets have been extensive and intrusive to the VFS. Worse there have been a number of camps all disagreeing as to the most sensible solution.
For a number of series we have carried the AUFS/AUFS2 patch kit as an Ubuntu add on. This has been a solid performer in this space and served our purposes well. About a year ago now talk began upstream on what approach would be acceptable to upstream. This has resulted in a proposed for an integrated VFS based solution for union filesystems called union-mounts. Patches have been circulating for the best part of a year and we skirted with them for the Lucid cycle, at that time they were feature incomplete preventing full testing.
Recently updated patches have been circulated which should be feature complete, and we are planning to provide kernels enabled for union-mount for testing in a PPA. Should testing there prove good we will consider switching to this solution for our live CDs. Watch this space as they say.