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*
* Device table
*
* The device table is a structure required by each
* block device.  It contains two sets of list
* headers, plus a device busy flag, and error retry
* count.  The list headers are the same as in the
* buffer headers.  One points to the list of buffers
* currently associated with the device while the
* other one may be used by the dvice driver as the
* io queue header.
*

* struct dtab

 base 0

dtdfl rmb 2 device buffer list fwd link
dtdbl rmb 2 device buffer list back link
dtqfl rmb 2 device io queue fwd link
dtqbl rmb 2 device io queue back link
dtbusy rmb 1 device busy flag
dtrtry rmb 1 device error retry count
dtspr rmb 2 device spare bytes (future use)

DVTSIZ equ * device table size
