Use mirage-logs library for log reporter

Also, configure Xen debug messages to go to the log ring buffer but not
the console (they will be shown only if an error occurs).

.travis.yml

@@ -19,4 +19,4 @@ addons:
     - camlp4-extra
     - time
 env:
-  - FORK_USER=talex5 FORK_BRANCH=unikernel OCAML_VERSION=4.02 MIRAGE_BACKEND=xen PINS="mirage-xen:https://github.com/talex5/mirage-platform.git#mm mirage-qubes:https://github.com/talex5/mirage-qubes.git mirage-nat:https://github.com/talex5/mirage-nat.git#simplify-checksum tcpip:https://github.com/mirage/mirage-tcpip.git"
+  - FORK_USER=talex5 FORK_BRANCH=unikernel OCAML_VERSION=4.02 MIRAGE_BACKEND=xen PINS="mirage-xen:https://github.com/talex5/mirage-platform.git#mm mirage-qubes:https://github.com/talex5/mirage-qubes.git mirage-nat:https://github.com/talex5/mirage-nat.git#simplify-checksum tcpip:https://github.com/mirage/mirage-tcpip.git mirage-logs:https://github.com/talex5/mirage-logs.git"

README.md

@@ -23,6 +23,7 @@ To build (tested by creating a fresh Fedora 23 AppVM in Qubes):
         opam pin add -y tcpip https://github.com/mirage/mirage-tcpip.git
         opam pin add -y mirage-qubes https://github.com/talex5/mirage-qubes.git
         opam pin add -y mirage-nat 'https://github.com/talex5/mirage-nat.git#simplify-checksum'
+        opam pin add -y mirage-logs https://github.com/talex5/mirage-logs.git
         opam install mirage
 
 3. Build mirage-firewall:

config.ml

@@ -7,8 +7,8 @@ open Mirage
 
 let main =
   foreign
-    ~libraries:["mirage-net-xen"; "tcpip.stack-direct"; "tcpip.xen"; "mirage-qubes"; "mirage-nat"]
-    ~packages:["vchan"; "cstruct"; "tcpip"; "mirage-net-xen"; "mirage-qubes"; "mirage-nat"]
+    ~libraries:["mirage-net-xen"; "tcpip.stack-direct"; "tcpip.xen"; "mirage-qubes"; "mirage-nat"; "mirage-logs"]
+    ~packages:["vchan"; "cstruct"; "tcpip"; "mirage-net-xen"; "mirage-qubes"; "mirage-nat"; "mirage-logs"]
     "Unikernel.Main" (clock @-> job)
 
 let () =

mirage_logs.ml

@@ -1,36 +0,0 @@
-(* Copyright (C) 2015, Thomas Leonard <thomas.leonard@unikernel.com>
-   See the README file for details. *)
-
-let buf = Buffer.create 200
-let log_fmt = Format.formatter_of_buffer buf
-
-let string_of_level =
-  let open Logs in function
-  | App -> "APP"
-  | Error -> "ERR"
-  | Warning -> "WRN"
-  | Info -> "INF"
-  | Debug -> "DBG"
-
-let fmt_timestamp tm =
-  let open Clock in
-  Printf.sprintf "%04d-%02d-%02d %02d:%02d.%02d"
-    (tm.tm_year + 1900) (tm.tm_mon + 1) tm.tm_mday tm.tm_hour tm.tm_min tm.tm_sec
-
-module Make (C : V1.CLOCK) = struct
-  let init_logging () =
-    let report src level ~over k msgf =
-      let now = C.time () |> Clock.gmtime |> fmt_timestamp in
-      let lvl = string_of_level level in
-      let k _ =
-        let msg = Buffer.contents buf in
-        Buffer.clear buf;
-        output_string stderr (msg ^ "\n");
-        flush stderr;
-        MProf.Trace.label msg;
-        over ();
-        k () in
-      msgf @@ fun ?header:_ ?tags:_ fmt ->
-      Format.kfprintf k log_fmt ("%s: %s [%s] " ^^ fmt) now lvl (Logs.Src.name src) in
-    Logs.set_reporter { Logs.report }
-end

mirage_logs.mli

@@ -1,14 +0,0 @@
-(* Copyright (C) 2015, Thomas Leonard <thomas.leonard@unikernel.com>
-   See the README file for details. *)
-
-(** Mirage support for Logs library. *)
-
-module Make (Clock : V1.CLOCK) : sig
-  val init_logging : unit -> unit
-  (** [init_logging ()] configures the Logs library to log to stderr,
-      with time-stamps provided by [Clock].
-      If logs are written faster than the backend can consume them,
-      the whole unikernel will block until there is space (so log messages
-      will not be lost, but unikernels generating a lot of log output
-      may run slowly). *)
-end

unikernel.ml

@@ -11,10 +11,13 @@ module Log = (val Logs.src_log src : Logs.LOG)
 let () =
   let open Logs in
   (* Set default log level *)
-  set_level (Some Logs.Info)
+  set_level (Some Logs.Info);
+  (* Debug-level logging for XenStore while tracking down occasional EACCES error. *)
+  Src.list () |> List.find (fun src -> Src.name src = "xenstore.client") |> fun xs ->
+  Src.set_level xs (Some Debug)
 
 module Main (Clock : V1.CLOCK) = struct
-  module Log_reporter = Mirage_logs.Make(Clock)
+  module Logs_reporter = Mirage_logs.Make(Clock)
   module Uplink = Uplink.Make(Clock)
 
   (* Set up networking and listen for incoming packets. *)
@@ -41,10 +44,16 @@ module Main (Clock : V1.CLOCK) = struct
       Uplink.listen uplink router
     ]
 
+  (* Control which of the messages that reach the reporter are logged to the console.
+     The rest will be displayed only if an error occurs.
+     Note: use the regular [Logs] configuration settings to determine which messages
+     reach the reporter in the first place. *)
+  let console_threshold _ = Logs.Info
+
   (* Main unikernel entry point (called from auto-generated main.ml). *)
   let start () =
     let start_time = Clock.time () in
-    Log_reporter.init_logging ();
+    Logs_reporter.(create ~ring_size:20 ~console_threshold () |> run) @@ fun () ->
     (* Start qrexec agent, GUI agent and QubesDB agent in parallel *)
     let qrexec = RExec.connect ~domid:0 () in
     let gui = GUI.connect ~domid:0 () in