Feature 57 (config and provisioning): modules declare config and provisions, their files rendered from templates; synced with main (issues of feature 57, 874)

modules/systemd-networkd/files/00-mesh0.network

@@ -0,0 +1,35 @@
+# Managed by the mesh (module systemd-networkd). Replaced on every push; edit
+# the catalogue instead.
+#
+# This machine's uplink is systemd-networkd's, and the mesh asks one thing of it
+# here (novox/hq ADR 0117): leave the private network's interface alone. mesh0
+# is the mesh's; the mesh brings it up and configures it itself. The mesh never
+# declares a link, an address, a route, a wireless network or its credentials,
+# nor a network file for any of this machine's own interfaces — those are
+# the operator's, and the link they make is the only channel the mesh reaches
+# this machine over.
+#
+# 00-: networkd applies the first .network file, in alphanumeric order across
+# every directory, that matches an interface, and ignores every later one even
+# if it matches too (systemd.network(5), [Match]). A catch-all of the operator's
+# — Name=*, Type=ether, a file with no [Match] at all — sorted before
+# this one would claim mesh0 first. 00 sorts before every numbered prefix the
+# man page recommends.
+#
+# Unmanaged=yes: "no attempts are made to bring up or configure matching links,
+# equivalent to when there are no matching network files" (systemd.network(5),
+# [Link], since 233). A match that ends the search, and does nothing else.
+#
+# No DNS setting, because none is needed: networkd never writes
+# /etc/resolv.conf. What it learns from a lease it hands only to
+# systemd-resolved, which the mesh does not run (novox/hq ADR 0196). So this
+# module declares the resolver file itself, beside this one, listing the
+# mesh's resolvers (novox/hq ADR 0223).
+#
+# The service is reloaded when this file changes, never restarted: a restart
+# drops the links networkd holds, this machine's channel to the mesh among them.
+[Match]
+Name=mesh0
+
+[Link]
+Unmanaged=yes