Dont check for temperatures in /thermal_zone where mode=disabled

[Saumya40-codes]

Relevant issue

Fixes: prometheus/node_exporter#2980

Current behaviour

• node_exporter checks for the contents of temp file even when mode is disabled due to which in the case when temp file contains a non desired value the thermal_zone collector fails and no longer gives its related metrics

Proposed solution

• Have an early exit and dont check rest if mode is set to disabled

Testing

• replacing github.com/prometheus/procfs in node_exporter go.mod to local dev setup of procfs and comparing the results in both

cc: @discordianfish

[SuperQ]

Typically we avoid making decisions like this in the library. Rather, we simply expose the mode as a raw attribute and allow the downstream consumer to decide what to do.

[Saumya40-codes]

Ohkk

Maybe thats something which can be handled from node exporter itself only?

here, as was stated in main issue, we check while reading the Zone temp and if the error turns out to be of type os.ErrInvalid then we can return an empty struct (and return an error when necessary (i.e. in the case of os.IsNotExist(err) && os.IsPermission(err)

[SuperQ]

Yes, we may need to refactor that error handling.

[SuperQ]

I'm thinking about #794 isntead. This error refactor allows us to always read as much as we can from a thermal zone.