libstore: allow for multiple daemon sockets with preference

this will let us configure more than one socket to connect/bind to,
which in turn lets us use posix acls on sockets for access control.
we will also need something like this for the final rpc transition.

Change-Id: I9c39f14906e9bf809055ab5c94bf687745b4f69e

misc/systemd/meson.build

@@ -1,4 +1,41 @@
-foreach config : [ 'nix-daemon.socket', 'nix-daemon.service', 'nix-daemon@.service' ]
+lix_daemon_socket_units = []
+
+# legacy sockets are handled specially for graceful fallback if nixos module
+# updates are not applied in lockstep with the socket split updates for lix.
+lix_daemon_socket_units += [ 'nix-daemon.socket' ]
+configure_file(
+  input : 'daemon.socket.in',
+  output : lix_daemon_socket_units[-1],
+  install : true,
+  install_dir : prefix / 'lib/systemd/system',
+  install_mode : 'rw-r--r--',
+  configuration : {
+    'storedir' : store_dir,
+    'localstatedir' : state_dir,
+    'bindir' : bindir,
+    'protocol' : 'legacy',
+    'kind' : 'combined',
+    'path' : 'socket',
+    'dirmode' : '0755',
+  },
+)
+configure_file(
+  input : 'daemon@.service.in',
+  output : 'nix-daemon@.service',
+  install : true,
+  install_dir : prefix / 'lib/systemd/system',
+  install_mode : 'rw-r--r--',
+  configuration : {
+    'storedir' : store_dir,
+    'localstatedir' : state_dir,
+    'bindir' : bindir,
+    'conflicts' : ' '.join(lix_daemon_socket_units),
+    'protocol' : 'legacy',
+    'kind' : 'combined',
+  },
+)
+
+foreach config : [ 'nix-daemon.service' ]
   configure_file(
     input : config + '.in',
     output : config,
@@ -9,6 +46,7 @@ foreach config : [ 'nix-daemon.socket', 'nix-daemon.service', 'nix-daemon@.servi
       'storedir' : store_dir,
       'localstatedir' : state_dir,
       'bindir' : bindir,
+      'conflicts' : ' '.join(lix_daemon_socket_units),
     },
   )
 endforeach

misc/systemd/nix-daemon.service.in

@@ -1,7 +1,7 @@
 [Unit]
 Description=Nix Daemon
 Documentation=man:nix-daemon https://docs.lix.systems/manual/lix/stable
-Conflicts=nix-daemon.socket
+Conflicts=@conflicts@
 RequiresMountsFor=@storedir@
 RequiresMountsFor=@localstatedir@
 RequiresMountsFor=@localstatedir@/nix/db