I *think* requests passing through xbd will always be sorted by the
underlying device driver in the dom0 OS.  Certainly if the requests
are heading for something like a vnd, sorting them in the domU kernel
is not the right thing to do, since they could then be sorted *three*
times.

But I cannot build a domU kernel (on the 3.0) branch with "options BUFQ_FCFS"
defined.  The other BUFQ options seem to work (READPRIO, PRIOCSCAN) but FCFS
produces a compile-time error in xbd.  I do not quite see why.

Does xbd already default to BUFQ_FCFS?  We should either make it so or
make BUFQ_FCFS the default with "options BUFQ_FCFS" in the XENU kernel.

Certainly vnd itself should default to BUFQ_FCFS.  Ultimately, in a stack
of NetBSD domU on NetBSD dom0, with xbd and vnd in the middle, only the
actual lowest-layer disk driver should sort.

-- 
  Thor Lancelot Simon	                                     tls@rek.tjls.com

  "We cannot usually in social life pursue a single value or a single moral
   aim, untroubled by the need to compromise with others."      - H.L.A. Hart