@benley, thanks for your PR! By analyzing the history of the files in this pull request, we identified @rickynils, @domenkozar and @urkud to be potential reviewers.

So useNetworkd is fine with services.dnsmasq but not networking.networkmanager.useDnsmasq?

However I've been noticing that my DNS server restarts every hour or so, and causes problems.

I see that the current configuration has this:

This means useDnsmasq is a very different option compared to using config.services.resolved and config.services.unbound, which is done automatically based on whether those services are enabled or not?

In order to make this configuration more intuitive, is it a good idea to eventually move to integration of networkmanager with an existing dnsmasq service just like how it's automatically selecting on the basis of these other unbound and resolved services and then deprecate useDnsmasq?

is it a good idea to eventually move to integration of networkmanager with an existing dnsmasq service

Yes, probably. One of the complicating factors is probably going to be networkmanager wanting to launch dnsmasq on its own, whereas nixos would normally launch it as a systemd unit. Maybe networkmanager has gained some systemd integration in a recent release? That would be cool.

Well, some users like me just want disable NetworkManager's builtin dns operations with config dns=none in NetworkManager.conf. But looks this commit make it impossible ;(

So how about revert to the old option style like #15560 did?

+      dns = mkOption {
+        type = types.enum [ "default" "dnsmasq" "none" ];
+        default = "default";
+        description = ''
+          Set the DNS (resolv.conf) processing mode.
+        '';
+      };

By the way, NetworkManager in NixOS use builtin dnsmasq with argument --conf-dir=/etc/NetworkManager/dnsmasq.d that most distros did, hope this will be improved so user could customize the builtin dnsmasq.