Re: [Libguestfs] [nbdkit PATCH v3 1/4] plugins: Don't use bogus errno from non-C plugins

Actually OCaml is a real compiled language, and the call from C to OCaml code (via caml_callback_exn) is a short piece of asm which preserves errno.

However you'll need to save errno around caml_enter_blocking_section since that unblocks and processes signals. IOW: static int pread_wrapper (void *h, void *buf, uint32_t count, uint64_t offset) { CAMLparam0 (); CAMLlocal3 (rv, strv, offsetv); + int saved_errno; ... rv = caml_callback3_exn (pread_fn, *(value *) h, strv, offsetv); + saved_errno = errno; if (Is_exception_result (rv)) { nbdkit_error ("%s", caml_format_exception (Extract_exception (rv))); caml_enter_blocking_section (); + errno = saved_errno; CAMLreturnT (int, -1);