The first byte of CDB USAGE FIELD contains the opcode value itself, not
0xff.
From SPC4 :
...
The first byte of the CDB USAGE FIELD
field shall contain the operation code for the command being queried.
...
REPORT SUPPORTED OPCODES.
Opcodes that are listed in the full list of all supported opcodes as taking
a service action should work to ask reporting option 2 (uses service action)
from but fail when asked for option 1 (no service action)
Similarly, opcodes that are flagged as not taking a service action should
work when used with option 1 but fail with option 2.
