The Grumpy Editor's guide to surviving the systemd debate [LWN.net]

The Grumpy Editor's guide to surviving the systemd debate

Posted Nov 16, 2014 21:39 UTC (Sun) by rgmoore (✭ supporter ✭, #75)
In reply to: The Grumpy Editor's guide to surviving the systemd debate by anselm
Parent article: The Grumpy Editor's guide to surviving the systemd debate

There's also the general point that writing configuration files as programs in a Turing-complete programming language is a gross violation of separation of policy from mechanism. I would probably lump it in with things that count as design anti-patterns.

to post comments

The Grumpy Editor's guide to surviving the systemd debate

Posted Nov 17, 2014 1:46 UTC (Mon) by neilbrown (subscriber, #359) [Link] (2 responses)

> There's also the general point that writing configuration files as programs in a Turing-complete programming language is a gross violation of separation of policy from mechanism.

Is it?
What if your policy is algorithmic in nature, or is more complex than the designers of the config file imagined?

TCL, lua, javascript are all languages that effectively allow very sophisticated tools to be configured in very sophisticated ways.
Are they all gross violations? (I almost added PHP to the list, but that might hurt my argument....)

If your configuration language supports substitution or conditionals - or maybe even just sequencing - then you probably want to start looking at a real language, because iteration probably isn't far away.

The line between "policy" and "implementation" is very real, but it is in your mind, not in the computer. And that is where it should be enforced.

The Grumpy Editor's guide to surviving the systemd debate

Posted Nov 18, 2014 0:07 UTC (Tue) by nix (subscriber, #2304) [Link] (1 responses)

TCL, lua, javascript are all languages that effectively allow very sophisticated tools to be configured in very sophisticated ways.
Are they all gross violations?

Further, at least two of these (Lua and Tcl) explicitly started as ways to write, well, Turing-complete configuration files: configury and program in the same language. Javascript didn't, but then it grew JSON, which is, well, exactly the same thing.

The Grumpy Editor's guide to surviving the systemd debate

Posted Nov 18, 2014 2:40 UTC (Tue) by zlynx (guest, #2285) [Link]

Sort of. But serious users of JSON never stick it into a string and eval(). That way lies nightmares and security holes.

In best practice JSON is non-executable.