Make sure that if we pull a buffer off of the read queue that it really
is a read request. Lower in this routine we base which queue we
dequeue the request from on its read/write state. Thus if a write
op ever ended up on the read queue, we'd explode (dereference NULL).
- rather than embedding bufq_state in driver softc,
have a pointer to the former.
- move bufq related functions from kern/subr_disk.c to kern/subr_bufq.c.
- rename method to strategy for consistency.
- move some definitions which don't need to be exposed to the rest of kernel
from sys/bufq.h to sys/bufq_impl.h.
(is it better to move it to kern/ or somewhere?)
- fix some obvious breakage in dev/qbus/ts.c. (not tested)
ad