systemd rules for closely-supervised knot-resolver service

This is a fully-socket-activated knot-resolver service that can run as
a non-priivleged user named knot-resolver.

.gitignore

@@ -23,7 +23,6 @@
 .libs
 .deps
 _obj
-tmp*
 /autom4te.cache/*
 /config.log
 /config.h

systemd/knot-resolver-control.socket

+[Unit]
+Description=Knot DNS Resolver control socket
+Documentation=man:kresd(8)
+Before=sockets.target
+
+[Socket]
+ListenStream=/run/knot-resolver/control
+FileDescriptorName=control
+Service=knot-resolver.service
+SocketMode=0660
+
+[Install]
+WantedBy=sockets.target

systemd/knot-resolver.service

+[Unit]
+Description=Knot DNS Resolver daemon
+## This is a socket-activated service:
+RefuseManualStart=true
+
+[Service]
+Type=notify
+WorkingDirectory=/run/knot-resolver/cache
+ExecStart=/usr/sbin/kresd
+User=knot-resolver
+Restart=on-failure
+
+[Install]
+WantedBy=sockets.target

systemd/knot-resolver.socket

+[Unit]
+Description=Knot DNS Resolver network listeners
+Documentation=man:kresd(8)
+Before=sockets.target
+
+[Socket]
+ListenStream=[::1]:53
+ListenDatagram=[::1]:53
+ListenStream=127.0.0.1:53
+ListenDatagram=127.0.0.1:53
+
+[Install]
+WantedBy=sockets.target

systemd/tmpfiles/knot-resolver.conf

+# tmpfiles.d(5) runtime directory for knot-resolver (kresd)
+#Type Path                            Mode UID           GID          Age Argument
+    d /run/knot-resolver              0750 root          root          -   -
+    d /run/knot-resolver/cache        0750 knot-resolver knot-resolver -   -
+    L /run/knot-resolver/cache/config 0750 knot-resolver knot-resolver -   /etc/knot-resolver/kresd.conf
+
+