[Libguestfs] [nbdkit PATCH] ocaml: Support .preconnect callback

[Eric Blake]

Somewhat of a mishmash between .open (in that it takes a bool readonly
parameter) and .config_complete (in that the C code returns an int,
but the Ocaml code either throws an exception or completes with unit).
I did not spot any existing testsuite coverage to modify for this, and
am relying on the fact that it compiles cleanly.

Signed-off-by: Eric Blake <eblake at redhat.com>
---
 plugins/ocaml/NBDKit.ml  | 12 ++++++++++--
 plugins/ocaml/NBDKit.mli |  4 +++-
 plugins/ocaml/ocaml.c    | 27 ++++++++++++++++++++++++++-
 3 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/plugins/ocaml/NBDKit.ml b/plugins/ocaml/NBDKit.ml
index 7002ac0..85c30a1 100644
--- a/plugins/ocaml/NBDKit.ml
+++ b/plugins/ocaml/NBDKit.ml
@@ -1,6 +1,6 @@
 (* hey emacs, this is OCaml code: -*- tuareg -*- *)
 (* nbdkit OCaml interface
- * Copyright (C) 2014-2019 Red Hat Inc.
+ * Copyright (C) 2014-2020 Red Hat Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
@@ -98,6 +98,8 @@ type 'a plugin = {
   thread_model : (unit -> thread_model) option;

   can_fast_zero : ('a -> bool) option;
+
+  preconnect : (bool -> unit) option;
 }

 let default_callbacks = {
@@ -145,6 +147,8 @@ let default_callbacks = {
   thread_model = None;

   can_fast_zero = None;
+
+  preconnect = None;
 }

 external set_name : string -> unit = "ocaml_nbdkit_set_name" "noalloc"
@@ -192,6 +196,8 @@ external set_thread_model : (unit -> thread_model) -> unit = "ocaml_nbdkit_set_t

 external set_can_fast_zero : ('a -> bool) -> unit = "ocaml_nbdkit_set_can_fast_zero"

+external set_preconnect : (bool -> unit) -> unit = "ocaml_nbdkit_set_preconnect"
+
 let may f = function None -> () | Some a -> f a

 let register_plugin plugin =
@@ -257,7 +263,9 @@ let register_plugin plugin =

   may set_thread_model plugin.thread_model;

-  may set_can_fast_zero plugin.can_fast_zero
+  may set_can_fast_zero plugin.can_fast_zero;
+
+  may set_preconnect plugin.preconnect

 external _set_error : int -> unit = "ocaml_nbdkit_set_error" "noalloc"

diff --git a/plugins/ocaml/NBDKit.mli b/plugins/ocaml/NBDKit.mli
index 06648b7..4cdf911 100644
--- a/plugins/ocaml/NBDKit.mli
+++ b/plugins/ocaml/NBDKit.mli
@@ -1,6 +1,6 @@
 (* hey emacs, this is OCaml code: -*- tuareg -*- *)
 (* nbdkit OCaml interface
- * Copyright (C) 2014-2019 Red Hat Inc.
+ * Copyright (C) 2014-2020 Red Hat Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
@@ -103,6 +103,8 @@ type 'a plugin = {
   thread_model : (unit -> thread_model) option;

   can_fast_zero : ('a -> bool) option;
+
+  preconnect : (bool -> unit) option;
 }
 (** The plugin fields and callbacks.  ['a] is the handle type. *)

diff --git a/plugins/ocaml/ocaml.c b/plugins/ocaml/ocaml.c
index cb69290..a7d188f 100644
--- a/plugins/ocaml/ocaml.c
+++ b/plugins/ocaml/ocaml.c
@@ -1,5 +1,5 @@
 /* nbdkit
- * Copyright (C) 2014-2019 Red Hat Inc.
+ * Copyright (C) 2014-2020 Red Hat Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
@@ -136,6 +136,8 @@ static value thread_model_fn;

 static value can_fast_zero_fn;

+static value preconnect_fn;
+
 /*----------------------------------------------------------------------*/
 /* Wrapper functions that translate calls from C (ie. nbdkit) to OCaml. */

@@ -726,6 +728,25 @@ can_fast_zero_wrapper (void *h)
   CAMLreturnT (int, Bool_val (rv));
 }

+static int
+preconnect_wrapper (int readonly)
+{
+  CAMLparam0 ();
+  CAMLlocal1 (rv);
+
+  caml_leave_blocking_section ();
+
+  rv = caml_callback_exn (preconnect_fn, Val_bool (readonly));
+  if (Is_exception_result (rv)) {
+    nbdkit_error ("%s", caml_format_exception (Extract_exception (rv)));
+    caml_enter_blocking_section ();
+    CAMLreturnT (int, -1);
+  }
+
+  caml_enter_blocking_section ();
+  CAMLreturnT (int, 1);
+}
+
 /*----------------------------------------------------------------------*/
 /* set_* functions called from OCaml code at load time to initialize
  * fields in the plugin struct.
@@ -815,6 +836,8 @@ SET(thread_model)

 SET(can_fast_zero)

+SET(preconnect)
+
 #undef SET

 static void
@@ -861,6 +884,8 @@ remove_roots (void)

   REMOVE (can_fast_zero);

+  REMOVE (preconnect);
+
 #undef REMOVE
 }

-- 
2.24.1