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

On Wed, 27 Nov 2024 16:37:05 +0100
Laurent Vivier <lvivier(a)redhat.com> wrote:

...
  On 27/11/2024 16:05, Stefano Brivio wrote:
  On Wed, 27 Nov 2024 15:55:00 +0100
 Laurent Vivier <lvivier(a)redhat.com> wrote:
   
  On 27/11/2024 15:48, Stefano Brivio wrote:  
  On Wed, 27 Nov 2024 15:41:30 +0100
 Laurent Vivier <lvivier(a)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(a)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.   
 In fact, in /usr/include/linux/if_ether.h they say:

 /* allow libcs like musl to deactivate this, glibc does not implement this. */

 So I think musl should set the value and then I found:

 #define __UAPI_DEF_ETHHDR       0

 in /usr/include/netinet/if_ether.h   
 
 Ah, I hadn't checked that yet.
   
  So I think the solution is to include
netinet/if_ether.h before linux/if_ether.h   
 
 Just in tcp_vu.c you mean? That's where we include <linux/if_ether.h>
 now.
 
 Any advantage over simply including linux/if_ether.h in passt.h as I
 did?   
 
 passt.h remains generic by not including linux specific headers.
 
 Something like that:
 
 diff --git a/tcp_vu.c b/tcp_vu.c
 index 05e2d1d..943b6d9 100644
 --- a/tcp_vu.c
 +++ b/tcp_vu.c
 @@ -13,7 +13,7 @@
   #include <netinet/tcp.h>
 
   #include <sys/socket.h>
 -
 +#include <netinet/if_ether.h>
   #include <linux/virtio_net.h>
 
   #include "util.h"
 diff --git a/vu_common.c b/vu_common.c
 index 0763ec0..299b5a3 100644
 --- a/vu_common.c
 +++ b/vu_common.c
 @@ -8,6 +8,7 @@
   #include <unistd.h>
   #include <sys/uio.h>
   #include <sys/eventfd.h>
 +#include <netinet/if_ether.h>
   #include <linux/virtio_net.h>
 
   #include "util.h"
  
Okay, that works as well, just tested on glibc and musl. I'll simply
fold it in 7/9 so that we don't break bisection with musl.

-- 
Stefano