illumos gate

To test this, I used the two interfaces on a system that had a single sensor:

rm@beowulf:~$ pfexec nvmeadm -v get-features nvme0 "Temperature Threshold" 
nvme0: Get Features
  Temperature Threshold
    Composite Over Temp. Threshold:         77C
    Composite Under Temp. Threshold:        0C

nvme0: SMART/Health Information
  Critical Warnings
    Available Space:                        OK
    Temperature:                            OK
    Device Reliability:                     OK
    Media:                                  OK
    Volatile Memory Backup:                 OK
  Temperature:                              32C
  Available Spare Capacity:                 100%
  Available Spare Threshold:                10%
  Device Life Used:                         0%
  Data Read:                                561GB
  Data Written:                             1033GB
  Read Commands:                            92989671
  Write Commands:                           56764216
  Controller Busy:                          1168min
  Power Cycles:                             123
  Power On:                                 464h
  Unsafe Shutdowns:                         52
  Uncorrectable Media Errors:               0
  Errors Logged:                            0
  Warning Composite Temperature Time:       0min
  Critical Composite Temperature Time:      0min
  Thermal Management Temp 1 Transition Count: 0
  Thermal Management Temp 2 Transition Count: 0
  Time for Thermal Management Temp 1:       0sec
  Time for Thermal Management Temp 2:       0sec

I also tested this on some other folks system that had multiple temperature sensors. This had initially discovered bugs in the implementation due to rounding and other issues. However, I verified those by manually interposing on them with mdb to set the default limits that were advertised. While there was some consideration as to whether the default limits for the 'temperature thresholds' should be exposed, I opted to make it clear here so someone can understand what the device is programmed with, even if the actual value isn't practical (an upper temperature threshold of say UINT16_MAX Kelvin).