From what I can see, operation succeeds, but prints a warning message.
The code that produces it is this:
My understanding is that the process originally had class “none” (0).
When resetting the IO priority class back to “none”, it adds the “class data” that was originally reported, but which is does nothing.
I think we can fix it by changing the line to:
if (m_originalNiceLevel < 0 || m_originalNiceClass == 0)
Only potential issue is that I do not know if all ionice versions expect the same. Potentially we would restore with a “slightly different” io-priority.
Long term, my plan is to make the backup run in an external process, which removes the problem, as we do not need to reset it, we just exit the process.
I am getting the same “Failed to reset background IO priority, exitcode: 0, stderr: ionice: ignoring given class data for none class” warning on “Debian 4.19.28-2~bpo9+1 (2019-03-27) x86_64” and “Duplicati 220.127.116.11_beta_2018-11-28” (Docker container from linuxserver/duplicati).
Can this warning be suppressed somehow as getting emails on this is misleading.