CA-388210: SMAPIv3 debugging: log PID

Log PID on successful and failed operations, and log full cmdline for newly spawned processes.

This can be used to debug stuck scripts, so that we know which invocation is the one that is stuck.

Signed-off-by: Edwin Török <edwin.torok@cloud.com>

Author: edwintorok

ocaml/xapi-storage-script/lib.ml

@@ -131,6 +131,7 @@ module Process = struct
 
     type t = {
         exit_status: (unit, exit_or_signal) Result.t
+      ; pid: int
       ; stdout: string
       ; stderr: string
     }
@@ -176,6 +177,7 @@ module Process = struct
   let run ~env ~prog ~args ~input =
     let ( let@ ) f x = f x in
     let@ p = with_process ~env ~prog ~args in
+    let pid = p#pid in
     let sender = send p#stdin input in
     let receiver_out = receive p#stdout in
     let receiver_err = receive p#stderr in
@@ -185,7 +187,7 @@ module Process = struct
         Lwt.both sender receiver >>= fun ((), (stdout, stderr)) ->
         p#status >>= fun status ->
         let exit_status = Output.exit_or_signal_of_unix status in
-        Lwt.return {Output.exit_status; stdout; stderr}
+        Lwt.return {Output.exit_status; pid; stdout; stderr}
       )
       (function
         | Lwt.Canceled as exn ->

ocaml/xapi-storage-script/lib.mli

@@ -65,6 +65,7 @@ module Process : sig
 
     type t = {
         exit_status: (unit, exit_or_signal) result
+      ; pid: int
       ; stdout: string
       ; stderr: string
     }
@@ -78,7 +79,7 @@ module Process : sig
     -> Output.t Lwt.t
   (** Runs a cli program, writes [input] into its stdin, then closing the fd,
       and finally waits for the program to finish and returns the exit status,
-      its stdout and stderr. *)
+      the pid, and its stdout and stderr. *)
 end
 
 module DirWatcher : sig

ocaml/xapi-storage-script/main.ml

@@ -477,6 +477,8 @@ let fork_exec_rpc :
     )
     >>>= fun input ->
     let input = compat_in input |> Jsonrpc.to_string in
+    debug (fun m -> m "Running %s" @@ Filename.quote_command script_name args)
+    >>= fun () ->
     Process.run ~env ~prog:script_name ~args ~input >>= fun output ->
     let fail_because ~cause description =
       fail
@@ -500,12 +502,13 @@ let fork_exec_rpc :
       with
       | Error _ ->
           error (fun m ->
-              m "%s failed and printed bad error json: %s" script_name
-                output.Process.Output.stdout
+              m "%s[%d] failed and printed bad error json: %s" script_name
+                output.pid output.Process.Output.stdout
           )
           >>= fun () ->
           error (fun m ->
-              m "%s failed, stderr: %s" script_name output.Process.Output.stderr
+              m "%s[%d] failed, stderr: %s" script_name output.pid
+                output.Process.Output.stderr
           )
           >>= fun () ->
           fail_because "non-zero exit and bad json on stdout"
@@ -516,12 +519,12 @@ let fork_exec_rpc :
         with
         | Error _ ->
             error (fun m ->
-                m "%s failed and printed bad error json: %s" script_name
-                  output.Process.Output.stdout
+                m "%s[%d] failed and printed bad error json: %s" script_name
+                  output.pid output.Process.Output.stdout
             )
             >>= fun () ->
             error (fun m ->
-                m "%s failed, stderr: %s" script_name
+                m "%s[%d] failed, stderr: %s" script_name output.pid
                   output.Process.Output.stderr
             )
             >>= fun () ->
@@ -532,7 +535,9 @@ let fork_exec_rpc :
       )
     )
     | Error (Signal signal) ->
-        error (fun m -> m "%s caught a signal and failed" script_name)
+        error (fun m ->
+            m "%s[%d] caught a signal and failed" script_name output.pid
+        )
         >>= fun () -> fail_because "signalled" ~cause:(Signal.to_string signal)
     | Ok () -> (
       (* Parse the json on stdout. We get back a JSON-RPC
@@ -544,8 +549,8 @@ let fork_exec_rpc :
       with
       | Error _ ->
           error (fun m ->
-              m "%s succeeded but printed bad json: %s" script_name
-                output.Process.Output.stdout
+              m "%s[%d] succeeded but printed bad json: %s" script_name
+                output.pid output.Process.Output.stdout
           )
           >>= fun () ->
           fail
@@ -554,7 +559,8 @@ let fork_exec_rpc :
             )
       | Ok response ->
           info (fun m ->
-              m "%s succeeded: %s" script_name output.Process.Output.stdout
+              m "%s[%d] succeeded: %s" script_name output.pid
+                output.Process.Output.stdout
           )
           >>= fun () ->
           let response = compat_out response in

ocaml/xapi-storage-script/test_lib.ml

@@ -103,12 +103,20 @@ let test_run_status =
   let module P = Process in
   let test () =
     let* output = P.run ~prog:"true" ~args:[] ~input:"" ~env:[] in
-    let expected = P.Output.{exit_status= Ok (); stdout= ""; stderr= ""} in
+    let expected =
+      P.Output.{exit_status= Ok (); pid= output.pid; stdout= ""; stderr= ""}
+    in
     Alcotest.(check output_c) "Exit status is correct" expected output ;
 
     let* output = P.run ~prog:"false" ~args:[] ~input:"" ~env:[] in
     let expected =
-      P.Output.{exit_status= Error (Exit_non_zero 1); stdout= ""; stderr= ""}
+      P.Output.
+        {
+          exit_status= Error (Exit_non_zero 1)
+        ; pid= output.pid
+        ; stdout= ""
+        ; stderr= ""
+        }
     in
     Alcotest.(check output_c) "Exit status is correct" expected output ;
 
@@ -121,15 +129,24 @@ let test_run_output =
   let test () =
     let content = "@@@@@@" in
     let* output = P.run ~prog:"cat" ~args:["-"] ~input:content ~env:[] in
-    let expected = P.Output.{exit_status= Ok (); stdout= content; stderr= ""} in
+    let expected =
+      P.Output.
+        {exit_status= Ok (); pid= output.pid; stdout= content; stderr= ""}
+    in
     Alcotest.(check output_c) "Stdout is correct" expected output ;
 
     let* output = P.run ~prog:"cat" ~args:[content] ~input:content ~env:[] in
     let stderr =
       Printf.sprintf "cat: %s: No such file or directory\n" content
     in
     let expected =
-      P.Output.{exit_status= Error (Exit_non_zero 1); stdout= ""; stderr}
+      P.Output.
+        {
+          exit_status= Error (Exit_non_zero 1)
+        ; pid= output.pid
+        ; stdout= ""
+        ; stderr
+        }
     in
     Alcotest.(check output_c) "Stderr is correct" expected output ;
     Lwt.return ()