Suricata

Exim was the tool that was brought up as an example, exim -bP dumps the active configuration, even if the config file is empty. It does have the benefit of a very flat, key=val configuration file format.

I think postfix was another one that was brought up http://www.postfix.org/postconf.1.html

Some thoughts on getting this done.

- All configuration needs to exist in a single datastore.
- This datastore can simply be a hard-coded YAML file that provides a complete fully default configuration.
- There also needs to be a "configuration" factory of sorts, as we have dynamic elements to our configuration. A common example of this is outputs, you can register multiple eve outputs so we can't hard code all these into a defualt configuration, but we can provide a default configuration for each eve logger, provided via a factory method of sorts.
- There also needs to be some precedence order to solve issue #1911 in a more generic way. Where when getting a configuration value with a prefix, the "fixed" set of vars is checked first, this makes sure stuff on the command line always takes precedence over values in the configuration file.
- I'd like this "central datastore" of config to be its own Rust crate that could also be used independently of Suricata for working with the configuration. We can get this pretty much for free by keeping it in mind from the start.
- Modules should not fall back to hard coded configuration they did not get from the main config datastore. The hardcoded value should be put into the datastore.

This should allow one to dump the complete default configuration, as well as a running config, which is the default configuration with the loaded configuration layered on top. With every possible configurable value in the output.

I've added relations to #1993 and #3636 as I think these would be much simpler to implement if built-in defaults would be "hard coded" yaml files. Enable all outputs would then just mean we select a different hard coded built-in default for outputs. Make sense?