This patch adds a Config::Listener abstract class that anyone can
inherit from and receive notifications when configuration values change.
We don't yet monitor file system changes, so these only work for changes
made by ConfigServer itself.
In order to receive these notifications, clients must monitor the domain
by calling monitor_domain(). Only pledged domains can be monitored.
Note that the client initiating the change does not get notified.
This API lets applications specify which configuration domains they
will be accessing throughout their lifetime. It works similarly in
spirit to the kernel's pledge().
You cannot pledge_domains() more than once, and once you have used it,
it's no longer possible to access any other configuration domain.
This is obviously just a first cut of this mechanism, and we may need
to tweak it further as we go.
It's not possible to connect to ConfigServer without having an event
loop available. This VERIFY makes it much easier to understand why
things are not working. :^)
ConfigServer is an IPC service that provides access to application
configuration and settings. The idea is to replace all uses of
Core::ConfigFile with IPC requests to ConfigServer.
This first cut of the API is pretty similar to Core::ConfigFile.
The old:
auto config = Core::ConfigFile::open_for_app("App");
auto value = config->read_entry("Group", "Key");
The new:
auto value = Config::read_string("App", "Group", "Key");
ConfigServer uses the ~/.config directory as its backing store
and all the files remain human-editable. :^)
