be issued/completed in order; that is, provide a barrier for I/O queues.
- Change the buffer driver queue links to a TAILQ, rather than using
a home-grown equivalent. Provide BUFQ_*() macros to manipulate buffer
queues; these deal with the barrier provided by B_ORDERED.
- Update disksort() accordingly, and provide 3 versions:
- disksort_cylinder(): historical disksort(), which keys on
b_cylinder (and b_blkno for the case when b_cylinder matches).
- disksort_blkno(): sorts only on b_blkno. Essentially the
same as disksort_cylinder(), but with fewer comparisons.
- disksort_tail(): requests are simply inserted into the queue
at the tail. This is provided as an option so that drivers
can simply have a pointer to the appropriate sort function.
Note that disksort() now pays attention to B_ORDERED.
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