Re: [PATCH nftables] include: fix for musl with iptables v1.8.11

[Phil Sutter <phil@nwl.cc>]

Hi Alyssa,

On Fri, Dec 20, 2024 at 12:10:02AM +0100, Alyssa Ross wrote:
> Since iptables commit 810f8568 (libxtables: xtoptions: Implement
> XTTYPE_ETHERMACMASK), nftables failed to build for musl libc:
> 
> 	In file included from /nix/store/bvffdqfhyxvx66bqlqqdmjmkyklkafv6-musl-1.2.5-dev/include/netinet/et…
> 	                 from /nix/store/kz6fymqpgbrj6330s6wv4idcf9pwsqs4-iptables-1.8.10-de…
> 	                 from src/xt.c:30:
> 	/nix/store/bvffdqfhyxvx66bqlqqdmjmkyklkafv6-musl-1.2.5-dev/include/netinet/if_ether.h:115:8: error: redefinition of 'struct ethhdr'
> 	  115 | struct ethhdr {
> 	      |        ^~~~~~
> 	In file included from ./include/linux/netfilter_bridge.h:8,
> 	                 from ./include/linux/netfilter_bridge/ebtables.h:1,
> 	                 from src/xt.c:27:
> 	/nix/store/bvffdqfhyxvx66bqlqqdmjmkyklkafv6-musl-1.2.5-dev/include/linux/if_ether.h:173:8: note: originally defined here
> 	  173 | struct ethhdr {
> 	      |        ^~~~~~
> 
> The fix is to use libc's version of if_ether.h before any kernel
> headers, which takes care of conflicts with the kernel's struct ethhdr
> definition by defining __UAPI_DEF_ETHHDR, which will tell the kernel's
> header not to define its own version.

What I don't like about this is how musl tries to force projects to not
include linux/if_ether.h directly. From the project's view, this is a
workaround not a fix.

> Signed-off-by: Alyssa Ross <hi@alyssa.is>
> ---
> A similar fix would solve the problem properly in iptables, which was 
> worked around with 76fce228 ("configure: Determine if musl is used for build").
> The __UAPI_DEF_ETHHDR is supposed to be set by netinet/if_ether.h, 
> rather than manually by users.

Why does 76fce228 not work for you?

Cheers, Phil