[Oneiric] Convert dm-raid45 to new block device plugging

[Leann Ogasawara]

Applied to Oneiric master-next.  Slightly modified to separate the
config change from the code change.  I also chose to revert the previous
disablement of CONFIG_DM_RAID45 instead so that it's easy to drop it
from existence upon the next rebase, eg.

Revert "UBUNTU: [Config] Disable CONFIG_DM_RAID45"

Thanks,
Leann

On Thu, 2011-05-26 at 16:42 +0200, Stefan Bader wrote:
> I was discussing this with the maintainer. According to him the dm-raid45 code 
> is not developed further. The goal would be to convert the dmraid user-space 
> side to use dm-raid (which is a target for RAID4/5/6 that uses md).
> 
> However looking at any user-space code that was available to the public right 
> now, I do not see any support for this. The table format, which is used to 
> create the device-mapper targets is substantially different between the two 
> modules. So user-space would have to change accordingly (and I am not sure how 
> well all features would be supported at the moment).
> 
> So, at least for Oneiric, I think we need to stay with the dm-raid45. I tested 
> the change below on an Intel soft-RAID5 and it survived an iozone and a bonnie++ 
> run.
> 
> -Stefan