[PATCH 1/3] nvmet: expose discovery subsystem in sysfs

[Sagi Grimberg]

>> Expose the discovery subsystem in sysfs instead of having it as
>> an internal structure. This requires the admin to manually
>> enable the discovery subsystem by linking it to a port, but
>> this can be seen as a feature as it will allows us to expose
>> subsystems without discovery subsystems and discovery subsystems
>> with no I/O subsystems.
> 
> ... and completely breaks any existing setup.

Yes, this needs to be backward compatible...