> be the best way to get XFS in the kernel. Note though that XFS also places
> requirements on the bottem-half of the file system, the buffer/vm system
> interface. It does this so that it can maintain commitments of
> isosynchronous (is that the right word?) transfers. So main-tree code

I believe that the realtime behaviour or Guaranteed Rate I/O 
(are you speaking about this?)
is an option which you may or may not have. If you want it, you must enable
it at the filesystem's creation date (a so-called realtime subvolume
must be added, which AFAIK should reside on a separate disk) and I
believe you also must purchase it separately (not sure about this). Linux's
XFS doesn't even have this option. So XFS could (theoretically) be
ported without it.

Please note that while I use IRIX, I never used guaranteed rate I/O, so
all what I say may be wrong.

Pavel