Comment 6 for bug 1841182

OK, to clarify my previous comment, the issue is not that /var/lib/cloud/data/set-hostname is _missing_, the issue is specifically that it is present but empty. Unfortunately, we don't have any logging from the code path used to write set-hostname (it uses cloudinit.atomic_helper.write_json which uses atomic_helper.write_file), so we can't be 100% sure that we aren't incorrectly writing out this empty file.

So, I think this breaks down into three things:

1) We should improve the logging situation there (just filed bug 1843276)
2) We should work out why the file ends up empty in this case
3) We should gracefully treat an empty file as an absent file (probably with a WARNING?), because I think that's the best we can do once we find ourselves in that situation

(2) and (3) should _probably_ be separate bugs, but without (1) it's not 100% clear that that's the case so I haven't filed anything separate yet.