Re: [PATCH] MacOS: Handle changes to args in xdrproc_t

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On 10/28/2013 12:05 PM, Doug Goldstein wrote:
> With Mac OS X 10.9, xdrproc_t is no longer defined as:
> 
> typedef bool_t (*xdrproc_t) (XDR *, void *, ...);
> 
> but instead as
> 
> typedef bool-t (*xdrproc_t) (XDR *, void *, unsigned int);
> 
> The rationale explained in the header is that using a vararg is
> incorrect and has a potential to change the ABI slightly. They decided
> to specify the exact number of parameters and for compatibility with old
> code decided to make the signature require 3 arguments. The third
> argument is ignored for cases that its not used and its recommended to
> supply a 0.
> ---
>  configure.ac            | 41 +++++++++++++++++++++++++++++++++++++++++
>  src/rpc/virnetmessage.c | 10 ++++++++--
>  2 files changed, 49 insertions(+), 2 deletions(-)
> 

I'd like some feedback from someone else who can actually test this on
MacOS, as well as FreeBSD, but it does seem reasonable to get in 1.1.4.

> diff --git a/configure.ac b/configure.ac
> index 1c5b168..f2bae88 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -697,6 +697,47 @@ if test x"$with_remote" = x"yes" || test x"$with_libvirtd" = x"yes"; then
>        *) XDR_CFLAGS=$lv_cv_xdr_cflags ;;
>      esac
>      AC_SUBST([XDR_CFLAGS])

Not your fault, but we probably ought to move xdr stuff into
m4/virt-xdr.m4 - but that can wait till post-release.

> +      AC_DEFINE_UNQUOTED([XDRPROC_T_ARG_COUNT], [$lv_cv_xdrproc_t_args],
> +                         [number of arguments that xdrproc_t func ptr takes])

Seems reasonable; but I'm a bit worried about accepting args=2 in the
cases where we actually needed the varargs to pass 3.  It may be safer
to pass 3 always, unless we have empirical evidence that uclibc will
fail to compile if we don't limit to exactly 2 (and not just a thread
archives where they were contemplating forcing just 2, but where I don't
know if the thread was actually applied as a patch).

>  
> +#if XDRPROC_T_ARG_COUNT == 3
> +# define VIR_XDRPROC(proc, xdr, data) ((proc)((xdr), (data), 0))
> +#else
> +# define VIR_XDRPROC(proc, xdr, data) ((proc)((xdr), (data)))
> +#endif

This seems like a nice abstraction for the problem at hand.

Here's hoping we get someone to provide test results in a timely manner.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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