For a while now it's possible to specify an additional config file in
`wpa_supplicant`[1]. In contrast to the file specified via `-c` this was
supposed to be used for immutable settings and not e.g. additional
networks.
However I'm a little bit unhappy about the fact that one has to choose
between a fully imperative setup and a fully declarative one where the
one would have to write credentials for e.g. WPA2-enterprise networks
into the store.
The primary problem with the current state of `wpa_supplicant` is that
if the `SAVE_CONFIG` command is invoked (e.g. via `wpa_cli`), all known
networks will be written to `/etc/wpa_supplicant.conf` and thus all
declarative networks would get out of sync with the declarative
settings.
To work around this, I had to change the following things:
* The `networking.wireless`-module now uses `-I` for declarative config,
so the user-controlled mode can be used along with the
`networks`-option.
* I added an `ro`-field to the `ssid`-struct in the
`wpa_supplicant`-sources. This will be set to `1` for each network
specified in the config passed via `-I`.
Whenever config is written to the disk, those networks will be
skipped, so changes to declarative networks are only temporary.
[1] https://w1.fi/cgit/hostap/commit/wpa_supplicant?id=e6304cad47251e88d073553042f1ea7805a858d1
