Re: [PATCH iproute2] ip: Fix compilation break on old systems

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 13 Nov 2017 12:21:19 +0200
Leon Romanovsky <leon@kernel.org> wrote:

> From: Leon Romanovsky <leonro@mellanox.com>
> 
> As was reported [1], the iproute2 fails to compile on old systems,
> in Cong's case, it was Fedora 19, in our case it was RedHat 7.2, which
> failed with the following errors during compilation:
> 
> ipxfrm.c: In function ‘xfrm_selector_print’:
> ipxfrm.c:479:7: error: ‘IPPROTO_MH’ undeclared (first use in this
> function)
>   case IPPROTO_MH:
>        ^
> ipxfrm.c:479:7: note: each undeclared identifier is reported only once
> for each function it appears in
> ipxfrm.c: In function ‘xfrm_selector_upspec_parse’:
> ipxfrm.c:1345:8: error: ‘IPPROTO_MH’ undeclared (first use in this
> function)
>    case IPPROTO_MH:
>         ^                                                                                                                                                            make[1]: *** [ipxfrm.o] Error 1
> 
> The reason to it is the order of headers files. The IPPROTO_MH field is
> set in kernel's UAPI header file (in6.h), but only in case
> __UAPI_DEF_IPPROTO_V6 is set before. That define comes from other kernel's
> header file (libc-compat.h) and is set in case there are no previous
> libc relevant declarations.
> 
> In ip code, the include of <netdb.h> causes to indirect inclusion of
> <netinet/in.h> and it sets __UAPI_DEF_IPPROTO_V6 to be zero and prevents from
> IPPROTO_MH declaration.
> 
> This patch takes the simplest possible approach to fix the compilation
> error by checking if IPPROTO_MH was defined before and in case it
> wasn't, it defines it to be the same as in the kernel.
> 
> [1] https://www.spinics.net/lists/netdev/msg463980.html
> 
> Cc: Cong Wang <xiyou.wangcong@gmail.com>
> Cc: Riad Abo Raed <riada@mellanox.com>
> Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
> ---
>  ip/xfrm.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/ip/xfrm.h b/ip/xfrm.h
> index 8566d639..71be574d 100644
> --- a/ip/xfrm.h
> +++ b/ip/xfrm.h
> @@ -30,6 +30,10 @@
>  #include <linux/xfrm.h>
>  #include <linux/ipsec.h>
> 
> +#ifndef IPPROTO_MH
> +#define IPPROTO_MH              135
> +#endif
> +

Is there some way to add an additional header to the file instead?
Doing local definitions seems like it might cause a future issue.