[Libguestfs] [libnbd PATCH v2 2/5] ocaml: tests: Fix error handling

[Eric Blake]

Like a lot of the C examples, the aio copy test ignores read and write
errors in the completion callback, which can cause silent data
corruption. The failure in the test is not critical, but this is a bad
example that may be copied by developers to a real application.

The test dies with an assertion failure now if completion callback
fails.  Tested with the temporary patch of:

| diff --git i/ocaml/tests/test_590_aio_copy.ml w/ocaml/tests/test_590_aio_copy.ml
| index a0339c8b..332bf31b 100644
| --- i/ocaml/tests/test_590_aio_copy.ml
| +++ w/ocaml/tests/test_590_aio_copy.ml
| @@ -120,7 +120,8 @@ let
|    let dst = NBD.create () in
|    NBD.set_handle_name dst "dst";
|    NBD.connect_command src ["nbdkit"; "-s"; "--exit-with-parent"; "-r";
| -                           "pattern"; sprintf "size=%d" disk_size];
| +                           "--filter=error"; "pattern"; "error-pread-rate=1";
| +                           sprintf "size=%d" disk_size];
|    NBD.connect_command dst ["nbdkit"; "-s"; "--exit-with-parent";
|                             "memory"; sprintf "size=%d" disk_size];
|    asynch_copy src dst
---
 ocaml/tests/test_590_aio_copy.ml | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/ocaml/tests/test_590_aio_copy.ml b/ocaml/tests/test_590_aio_copy.ml
index 11d89256..a0339c8b 100644
--- a/ocaml/tests/test_590_aio_copy.ml
+++ b/ocaml/tests/test_590_aio_copy.ml
@@ -1,6 +1,6 @@
 (* hey emacs, this is OCaml code: -*- tuareg -*- *)
 (* libnbd OCaml test case
- * Copyright (C) 2013-2019 Red Hat Inc.
+ * Copyright (C) 2013-2022 Red Hat Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -45,7 +45,8 @@ let
    * next iteration of the loop.
    *)
   let writes = ref [] in
-  let read_completed buf offset _ =
+  let read_completed buf offset err =
+    assert (!err = 0);
     bytes_read := !bytes_read + NBD.Buffer.size buf;
     (* Get ready to issue a write command. *)
     writes := (buf, offset) :: !writes;
@@ -56,7 +57,8 @@ let
   (* This callback is called when any pwrite to the destination
    * has completed.
    *)
-  let write_completed buf _ =
+  let write_completed buf err =
+    assert (!err = 0);
     bytes_written := !bytes_written + NBD.Buffer.size buf;
     (* By returning 1 here we auto-retire the pwrite command. *)
     1
-- 
2.34.1