Temperature input plugin stops working when WiFi is turned off

[marcv81]

Relevant telegraf.conf:

[[inputs.temp]]

System info:

• Telegraf 1.10.1-1 installed from .deb package / Ubuntu 16.04 + Kernel 5.0
• Intel Wireless LAN hardware, iwlwifi module

Steps to reproduce:

1. Enable WiFi, connect to a network
2. Enable the inputs.temp plugin
3. Observe that the plugin is working correctly: various temp metrics should exist, including one called temp,sensor=iwlwifi_input
4. Disconnect from the network, turn off WiFi

Expected behavior:

No new metrics should be produced for temp,sensor=iwlwifi_input. New metrics should still be produced for everything else in temp.

Actual behavior:

No new metric is produced for anything in temp.

Additional info:

Apr 08 14:36:50 telegraf[6305]: 2019-04-08T06:36:50Z E! [inputs.temp]: Error in plugin: error getting temperatures info: read /sys/class/hwmon/hwmon4/temp1_input: no data available

[glinton]

We could add to the check here to return only if len(temps) == 0, but you could still potentially see partial or missing data. This is due to the upstream gopsutil library returning on file read errors.

This seems like an upstream issue, as implementing the len workaround would create a new issue for incomplete data.

[danielnelson]

@glinton Could you create a new issue on the gopsutil project and link to it here. I agree the upstream code should probably skip errors.

[marcv81]

Related PR: #5941.