According to the MPT2 spec, task management commands are
serialized, and so no I/O should start while task management
commands are active.
So, to comply with that, freeze the SIM queue before we send any
task management commands (abort, target reset, etc.) down to the
IOC. We unfreeze the queue once the task management command
completes.
It isn't clear from the spec whether multiple simultaneous task
management commands are supported. Right now it is possible to
have multiple outstanding task management commands, especially in
the abort case. Multiple outstanding aborts do complete
successfully, so it may be supported.
We also don't yet have any recovery mechanism (e.g. reset the IOC)
if the task management command fails.
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