CA-387560 add support for more systemd execution types

We use systemd to start transient services. So far, we use the Simple
type but would like to add oneshot and potentially more.

Signed-off-by: Christian Lindig <[email protected]>

ocaml/forkexecd/lib/fe_systemctl.ml

@@ -26,12 +26,25 @@ let action ~service action =
   in
   ()
 
+(** Systemd execution type *)
+module Type = struct
+  type t = Simple | OneShot | Forking
+
+  let to_string = function
+    | Simple ->
+        "simple"
+    | OneShot ->
+        "oneshot"
+    | Forking ->
+        "forking"
+end
+
 let default_env = ["PATH=" ^ String.concat ":" Forkhelpers.default_path]
 
 let run_path = "/run/systemd/system/"
 
 let start_transient ?(env = Array.of_list default_env) ?(properties = [])
-    ~service cmd args =
+    ~exec_ty ~service cmd args =
   let syslog_key = service in
   let service = syslog_key ^ ".service" in
   let destination = Filename.concat run_path service in
@@ -47,7 +60,7 @@ let start_transient ?(env = Array.of_list default_env) ?(properties = [])
        ; ("StandardError", "inherit")
        ; ("StartLimitInterval", "0") (* no rate-limit, for bootstorms *)
        ; ("ExecStart", String.concat " " (cmd :: List.map Filename.quote args))
-       ; ("Type", "simple")
+       ; ("Type", Type.to_string exec_ty)
          (* our systemd is too old, and doesn't support 'exec' *)
        ; ("Restart", "no")
          (* can't restart the device-model, it would've lost all state already *)
@@ -118,11 +131,12 @@ let is_active ~service =
 let exists ~service =
   Sys.file_exists (Filename.concat run_path (service ^ ".service"))
 
-let start_transient ?env ?properties ~service cmd args =
+let start_transient ?env ?properties ?(exec_ty = Type.Simple) ~service cmd args
+    =
   if exists ~service then
     (* this can only happen if there is a bug in the caller *)
     invalid_arg (Printf.sprintf "Tried to start %s twice" service) ;
-  try start_transient ?env ?properties ~service cmd args
+  try start_transient ?env ?properties ~exec_ty ~service cmd args
   with e ->
     Backtrace.is_important e ;
     (* If start failed we do not know what state the service is in:

ocaml/forkexecd/lib/fe_systemctl.mli

@@ -18,21 +18,29 @@ type status = {
   ; active_state: string
 }
 
+module Type : sig
+  type t = Simple | OneShot | Forking
+
+  val to_string : t -> string
+end
+
 val start_transient :
      ?env:string array
   -> ?properties:(string * string) list
+  -> ?exec_ty:Type.t
   -> service:string
   -> string
   -> string list
   -> unit
-(** [start_transient ?env ?properties ~service cmd args] generates and starts a transient systemd
- * [service] that will execute [cmd args].
- * stdout/stderr from the service is redirected to syslog with [service] as syslog key.
- * Additional [properties] can be specified that are written into the systemd unit file's [Service]
- * section.
- * By default the service is not auto-restarted when it fails, and there is a 10s timeout between
- * SIGTERM and SIGKILL on stop.
- * On failure it raises [Spawn_internal_error(stderr, stdout, Unix.process_status)] *)
+(** [start_transient ?env ?properties ~service cmd args] generates and
+    starts a transient systemd [service] that will execute [cmd args].
+    stdout/stderr from the service is redirected to syslog with
+    [service] as syslog key.  Additional [properties] can be specified
+    that are written into the systemd unit file's [Service] section.  By
+    default the service is not auto-restarted when it fails, and there
+    is a 10s timeout between SIGTERM and SIGKILL on stop.  On failure it
+    raises [Spawn_internal_error(stderr, stdout, Unix.process_status)]
+    *)
 
 val is_active : service:string -> bool
 (** [is_active ~service] checks whether the [service] is still running *)