drivers/main: warn on unrecognised parameters

[systemcrash]

Exiting is rather pointless if the driver does not recognise the parameter. The driver ignores it anyway (?).

This is intended to resolve a problem where we use nut in openwrt and a startup script does not know what parameters a driver can take in advance (and users might not have read the man page), but execution halts if an unknown parameter is encountered.

Nothing bad happens, and a warning can be printed instead of an error.

See also https://utcc.utoronto.ca/~cks/space/blog/programming/ErrorsShouldRequireFixing

[jimklimov]

Well, this is arguable TBH. If the program is asked to do something it has no idea about, it can at least deduce it won't fulfill the user's explicit requirement. It may be in fact misleading to proceed as if nothing happened for no reason, and the user should fix the config. (We do e.g. ignore user/group ID changes on platforms where they can not be done, but there's a reason for that. And maybe that's not too right too.)

WDYT @aquette @clepple @gdt ?

[gdt]

I lean to continuing to error on bad params.

[AppVeyorBot]

✅ Build nut 2.8.4.3976-master completed (commit 4fd2bd7040 by @systemcrash)

[jimklimov]

Posted on mailing list to gather more opinions about which approach is the lesser evil - to crash, or to pass and so hide user config errors (and welcome strange unexpected behaviours where something does not work as it presumably was told to).

On the technical side, ignoring an unknown option should indeed be same as never receiving it. To me the problem is more of a social one, where somebody explicitly writes a config file leading to/due to certain expectations, and those expectations are not met by a driver version that has no idea about that concept. So by the principle of least surprise, aborting when not knowing how to proceed (and so asking the local expert human for instructions) is the correct way.

[kellybyrd]

Another vote for: "stop on unknown params". The system cannot know if the user intended to give a valid newer parameter to an older version or if the user misspelled a parameter that is valid to the current version. IMO, halting on not recognized input is the least surprising thing the NUT can do.

If not, where does this stop? what if config files have options that are not valid with the current release or misspelled?