[Libguestfs] [libnbd PATCH] generator: Add #define witnesses for all API

Make it easier for C libraries to consume arbitrary versions of libnbd, by giving a probe for which functions the current version of the library exports. --- I'm fuzzy enough on OCaml that I'll get review for this, although I like the resulting libnbd.h. generator/generator | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) diff --git a/generator/generator b/generator/generator index db7c10f..7d0ea3f 100755 --- a/generator/generator +++ b/generator/generator @@ -2712,6 +2712,12 @@ let print_extern name args ret = print_call name args ret; pr ";\n" +let print_extern_and_define name args ret = + let name_upper = String.uppercase_ascii name in + print_extern name args ret; + pr "#define LIBNBD_HAVE_NBD_%s 1\n" name_upper; + pr "\n" + let generate_include_libnbd_h () = generate_header CStyle; @@ -2729,14 +2735,23 @@ let generate_include_libnbd_h () = List.iter (fun (n, i) -> pr "#define LIBNBD_%-30s %d\n" n i) constants; pr "\n"; pr "extern struct nbd_handle *nbd_create (void);\n"; + pr "#define LIBNBD_HAVE_NBD_CREATE 1\n"; + pr "\n"; pr "extern void nbd_close (struct nbd_handle *h);\n"; + pr "#define LIBNBD_HAVE_NBD_CLOSE 1\n"; + pr "\n"; pr "extern const char *nbd_get_error (void);\n"; + pr "#define LIBNBD_HAVE_NBD_GET_ERROR 1\n"; + pr "\n"; pr "extern int nbd_get_errno (void);\n"; + pr "#define LIBNBD_HAVE_NBD_GET_ERRNO 1\n"; + pr "\n"; pr "extern int nbd_add_close_callback (struct nbd_handle *h,\n"; pr " nbd_close_callback cb, void *data);\n"; + pr "#define LIBNBD_HAVE_NBD_ADD_CLOSE_CALLBACK 1\n"; pr "\n"; List.iter ( - fun (name, { args; ret }) -> print_extern name args ret + fun (name, { args; ret }) -> print_extern_and_define name args ret ) handle_calls; pr "\n"; pr "#endif /* LIBNBD_H */\n" @@ -2933,6 +2948,13 @@ in detail. If you want an overview of using the API, or to see how to call the API from other programming languages, start with libnbd(3). +For the sake of conditional compilation across a range of libnbd +versions, where a client may take advantage of newer API when present +but gracefully continue to compile even when it is not, all functions +declared in B<E<lt>libnbd.hE<gt>> have a corresponding witness macro +with prefix C<LIBNBD_HAVE_>. For example, C<nbd_create> has a +counterpart macro C<LIBNBD_HAVE_NBD_CREATE> defined to C<1>. + =head1 CREATE, GET AND CLOSE HANDLES struct nbd_handle *nbd; -- 2.20.1