Re: [PATCH] musl: fix conflict on ethhdr definition

[Stefano Brivio <sbrivio@redhat.com>]

On Wed, 27 Nov 2024 15:41:30 +0100
Laurent Vivier <lvivier@redhat.com> wrote:

> there is a conflict between netinet/if_ether.h provided by musl and
> linux/if_ether.h provided by the linux headers:
> 
>   In file included from passt.h:185,
>                    from tcp_vu.c:21:
>   /usr/include/netinet/if_ether.h:115:8: error: redefinition of 'struct ethhdr'
>     115 | struct ethhdr {
>         |        ^~~~~~
>   In file included from /usr/include/linux/virtio_net.h:32,
>                    from tcp_vu.c:17:
>   /usr/include/linux/if_ether.h:173:8: note: originally defined here
>     173 | struct ethhdr {
>         |        ^~~~~~
> 
> The kernel headers provide a flag to disable the definition in this case,
> __UAPI_DEF_ETHHDR (see /usr/include/linux/if_ether.h comment).
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  Makefile | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index cb7448079de5..2aa56ada65fd 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -33,6 +33,9 @@ FLAGS +=  $(FORTIFY_FLAG) -O2 -pie -fPIE
>  FLAGS += -DPAGE_SIZE=$(shell getconf PAGE_SIZE)
>  FLAGS += -DVERSION=\"$(VERSION)\"
>  FLAGS += -DDUAL_STACK_SOCKETS=$(DUAL_STACK_SOCKETS)
> +ifeq (musl, $(word 4,$(subst -, ,$(TARGET))))
> +FLAGS += -D__UAPI_DEF_ETHHDR=0
> +endif

Uh oh, I just solved this locally (I was about to push, but I stopped
in time) by simply including <linux/if_ether.h> instead of
<netinet/if_ether.h> from passt.h.

I'm not sure what's the best solution: mine is simpler, but I'm not
really fond of including Linux-specific stuff if there's no need for
it, so I'd slightly prefer yours.

On the other hand, it's not just for musl. If somebody tries to build
this against, say, uClibc-ng (no reports about that yet), they will
probably run into trouble as well.

Or should we just unconditionally #define __UAPI_DEF_ETHHDR=0 just
before including <linux/virtio_net.h>?

-- 
Stefano