CP-48195: Add with_tracing helper function

Adds `with_tracing` helper function to `forkhelpers.ml`.

This is to show that there are no more cycle dependecies between
`tracing` library and `forexecd` and it will be used in a follow-up PR
to instrument `forkhelpers` with tracing.

Signed-off-by: Gabriel Buica <danutgabriel.buica@cloud.com>

Author: GabrielBuica

forkexec.opam

@@ -21,6 +21,7 @@ depends: [
   "xapi-log"
   "xapi-stdext-pervasives"
   "xapi-stdext-unix"
+  "xapi-tracing"
 ]
 synopsis: "Sub-process control service for xapi"
 description:

forkexec.opam.template

@@ -19,6 +19,7 @@ depends: [
   "xapi-log"
   "xapi-stdext-pervasives"
   "xapi-stdext-unix"
+  "xapi-tracing"
 ]
 synopsis: "Sub-process control service for xapi"
 description:

ocaml/forkexecd/lib/dune

@@ -12,6 +12,7 @@
    xapi-log
    xapi-stdext-pervasives
    xapi-stdext-unix
+   xapi-tracing
  )
  (preprocess
   (pps ppx_deriving_rpc)))

ocaml/forkexecd/lib/forkhelpers.ml

@@ -36,6 +36,10 @@ let test_path =
 
 let runtime_path = Option.value ~default:"/var" test_path
 
+let _with_tracing ?tracing ~name f =
+  let name = Printf.sprintf "forkhelpers.%s" name in
+  Tracing.with_tracing ?parent:tracing ~name f
+
 let finally = Xapi_stdext_pervasives.Pervasiveext.finally
 
 type pidty = Unix.file_descr * int

ocaml/tests/test_observer.ml

@@ -71,9 +71,7 @@ module TracerProvider = struct
   let find_provider_exn ~name =
     let providers = get_tracer_providers () in
     match
-      List.find_opt
-        (fun x -> TracerProvider.get_name_label x = name)
-        providers
+      List.find_opt (fun x -> TracerProvider.get_name_label x = name) providers
     with
     | Some provider ->
         provider