RFC: "persistent state" directory default/config/API
I'd like to add a "persistent state" directory with a hard-coded
default, config directive and API equivalent to the runtimdir in
config.layout, DefaultRuntimeDir directive and
ap_runtime_dir_relative(). The "runtime" directory is used for
transient state which disappears and can be deleted once the server is
stopped. This can be safely stored in tmpfs or even created & deleted
on the fly. A "persistent state" directory would be for data which is
expected to persist across restarts.
Example users are the mod_dav_fs lock database, mod_md's MD data store.
With an API & default, these can have hard-coded default paths so the
modules work without needing configuration. The proxy cache root could
count here too.
I'm not sure about naming, maybe simply:
DefaultStateDir -- ap_state_dir_relative()
and use "statedir" in config.layout since localstatedir is already used
and is typically set to /var or $prefix.
For Linux/FHS type layouts, statedir could be set to e.g. /var/lib/httpd
and for layouts like "Apache", maybe $prefix/state or something like
that would be fine.