scheme for defining inline command queuing functions.
Prefer enums to #defines.
sys/dev/xen/blkfront/block.h
Replace inline function generation performed by the
XBDQ_COMMAND_QUEUE() macro with single instances of each
inline function (init, enqueue, dequeue, remove). This was
made possible by using queue indexes instead of bit flags
in the command structure, and passing the index enum as
an argument to the functions.
Improve panic/assert messages in the queue functions.
Combine queue data and stats into a single data structure
and declare an array of them instead of each queue individually.
Convert command flags, softc state, and softc flags to enums.
sys/dev/xen/blkfront/blkfront.c
Mechanical adjustments for new queue api.
Sponsored by: Spectra Logic Corporation
MFC after: 1 week
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