Experimental systemd socket activation

albatross.opam

@@ -32,6 +32,7 @@ depends: [
   "metrics" {>= "0.2.0"}
   "metrics-lwt" {>= "0.2.0"}
   "metrics-influx" {>= "0.2.0"}
+  "ocaml-systemd"
 ]
 build: [
   ["dune" "subst"] {pinned}

daemon/albatross_log.ml

@@ -148,7 +148,15 @@ let handle mvar ring s addr =
 
 let m = Vmm_core.conn_metrics "unix"
 
-let jump _ file read_only influx tmpdir =
+let server_socket systemd =
+  if systemd then
+    match Daemon.listen_fds () with
+    | [fd] -> Lwt.return (Lwt_unix.of_unix_file_descr fd)
+    | _ -> failwith "Unexpected number of sockets"
+  else
+    Vmm_lwt.server_socket `Log
+
+let jump _ systemd file read_only influx tmpdir =
   Sys.(set_signal sigpipe Signal_ignore) ;
   Albatross_cli.set_tmpdir tmpdir;
   Lwt_main.run
@@ -161,7 +169,7 @@ let jump _ file read_only influx tmpdir =
        Lwt.return_unit
      end else begin
        Albatross_cli.init_influx "albatross_log" influx;
-       Vmm_lwt.server_socket `Log >>= fun s ->
+       server_socket systemd >>= fun s ->
        let ring = Vmm_ring.create `Startup () in
        List.iter (Vmm_ring.write ring) entries ;
        let mvar = Lwt_mvar.create_empty () in
@@ -191,8 +199,12 @@ let read_only =
   let doc = "Only read log file and present entries" in
   Arg.(value & flag & info [ "read-only" ] ~doc)
 
+let systemd =
+  let doc = "Pass this flag when systemd socket activation is being used" in
+  Arg.(value & flag & info [ "systemd-socket-activation" ] ~doc)
+
 let cmd =
-  Term.(const jump $ setup_log $ file $ read_only $ influx $ tmpdir),
+  Term.(const jump $ setup_log $ systemd $ file $ read_only $ influx $ tmpdir),
   Term.info "albatross_log" ~version
 
 let () = match Term.eval cmd with `Ok () -> exit 0 | _ -> exit 1

daemon/dune

@@ -24,4 +24,4 @@
   (public_name albatross-log)
   (package albatross)
   (modules albatross_log)
-  (libraries albatross.cli albatross))
+  (libraries albatross.cli albatross systemd))

packaging/Linux/albatross_log.service

@@ -17,4 +17,5 @@ PIDFile=%t/albatross/log.pid
 RestrictAddressFamilies=AF_UNIX
 
 [Install]
+Also=albatross_log.socket
 WantedBy=multi-user.target

packaging/Linux/albatross_log.socket

@@ -0,0 +1,12 @@
+[Unit]
+Description=Albatross log socket
+PartOf=albatross_log.service
+
+[Socket]
+ListenStream=%t/albatross/util/log.sock
+SocketUser=albatross
+#SocketMode= # FIXME: permissions
+Accept=no
+
+[Install]
+WantedBy=sockets.target