Libguestfs - Jun 2019 - Re: [libnbd PATCH] Fix building with for ocaml < 4.06.0

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
---

Notes:
    This is the simplest solution suggested to me by Rich and it works.
    
    Most of autotools are not friends with me, so the other approach I tried,
with
    requiring at least OCaml 4.05.0, having this fix in only for OCaml <
4.06.0 and
    properly detecting and reporting that, was a bit ugly.
    
    You can see the configure.ac part of it here: http://ix.io/1L0o
    
    If that is preferred, then I can send that one instead.

 ocaml/nbd-c.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/ocaml/nbd-c.h b/ocaml/nbd-c.h
index 558581850807..45ae64d77209 100644
--- a/ocaml/nbd-c.h
+++ b/ocaml/nbd-c.h
@@ -27,6 +27,11 @@
 #include <caml/memory.h>
 #include <caml/mlvalues.h>
 
+// Workaround for OCaml < 4.06.0
+#ifndef Bytes_val
+#define Bytes_val(x) String_val(x)
+#endif
+
 extern void libnbd_finalize (value);
 extern void nbd_buffer_finalize (value);
 
-- 
2.21.0

On Wednesday, 12 June 2019 13:27:34 CEST Martin Kletzander
wrote:
> Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
> ---
> 
> Notes:
>     This is the simplest solution suggested to me by Rich and it works.
>     
>     Most of autotools are not friends with me, so the other approach I
tried, with
>     requiring at least OCaml 4.05.0, having this fix in only for OCaml <
4.06.0 and
>     properly detecting and reporting that, was a bit ugly.
>     
>     You can see the configure.ac part of it here: http://ix.io/1L0o
It is not that bad IMHO -- just ignore the "micro" part of the
version,
as it not needed, and use a similar approach of libguestfs:
https://github.com/libguestfs/libguestfs/blob/master/m4/guestfs-ocaml.m4#L41

-- 
Pino Toscano

On 6/12/19 6:27 AM, Martin Kletzander wrote:
> Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
> ---
> 
> Notes:
>     This is the simplest solution suggested to me by Rich and it works.
>     
>     Most of autotools are not friends with me, so the other approach I
tried, with
>     requiring at least OCaml 4.05.0, having this fix in only for OCaml <
4.06.0 and
>     properly detecting and reporting that, was a bit ugly.
I prefer the lightweight approach - all the more configure.ac does is
add the ability to do #ifdef-ery probing on things that don't originally
come with enough #ifdef witnesses; but here, the absence of Bytes_val is
all the more that you would probe for in configure.ac, making it not
worth the effort to add yet another macro just to work around the problem.

Which platform are you compiling on, and what OCaml version are you
using?  That said, I don't see any reason to not commit this patch.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

On Wed, Jun 12, 2019 at 01:27:34PM +0200, Martin Kletzander
wrote:
> Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
> ---
> 
> Notes:
>     This is the simplest solution suggested to me by Rich and it works.
>     
>     Most of autotools are not friends with me, so the other approach I
tried, with
>     requiring at least OCaml 4.05.0, having this fix in only for OCaml <
4.06.0 and
>     properly detecting and reporting that, was a bit ugly.
>     
>     You can see the configure.ac part of it here: http://ix.io/1L0o
>     
>     If that is preferred, then I can send that one instead.
> 
>  ocaml/nbd-c.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/ocaml/nbd-c.h b/ocaml/nbd-c.h
> index 558581850807..45ae64d77209 100644
> --- a/ocaml/nbd-c.h
> +++ b/ocaml/nbd-c.h
> @@ -27,6 +27,11 @@
>  #include <caml/memory.h>
>  #include <caml/mlvalues.h>
>  
> +// Workaround for OCaml < 4.06.0
> +#ifndef Bytes_val
> +#define Bytes_val(x) String_val(x)
> +#endif
> +
>  extern void libnbd_finalize (value);
>  extern void nbd_buffer_finalize (value);
The configure.ac changes are a bit more complex, and this should work
for versions of OCaml which have the bytes type but not this macro.
OCaml 4.02 introduced the bytes type in 2014, so this (probably - I
did not test) fixes things back to then.

So I will push this shortly, thanks.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org

On Wed, Jun 12, 2019 at 08:02:06AM -0500, Eric Blake
wrote:
>On 6/12/19 6:27 AM, Martin Kletzander wrote:
>> Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
>> ---
>>
>> Notes:
>>     This is the simplest solution suggested to me by Rich and it works.
>>
>>     Most of autotools are not friends with me, so the other approach I
tried, with
>>     requiring at least OCaml 4.05.0, having this fix in only for OCaml
< 4.06.0 and
>>     properly detecting and reporting that, was a bit ugly.
>
>I prefer the lightweight approach - all the more configure.ac does is
>add the ability to do #ifdef-ery probing on things that don't originally
>come with enough #ifdef witnesses; but here, the absence of Bytes_val is
>all the more that you would probe for in configure.ac, making it not
>worth the effort to add yet another macro just to work around the problem.
>
>Which platform are you compiling on, and what OCaml version are you
>using?  That said, I don't see any reason to not commit this patch.
>
Gentoo, OCaml 4.05.0 in the system, but 4.07.0 through opam.  I noticed I cannot
build it when I added it as a package and wanted to install it into the system.
>--
>Eric Blake, Principal Software Engineer
>Red Hat, Inc.           +1-919-301-3226
>Virtualization:  qemu.org | libvirt.org
>