Re: [PATCH iptables] include: fix build with kernel headers before 4.2

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On Sat, Nov 17, 2018 at 10:28:56PM +0200, Baruch Siach wrote:
> Hi Pablo,
> 
> Pablo Neira Ayuso writes:
> > On Fri, Nov 16, 2018 at 09:30:33AM +0200, Baruch Siach wrote:
> >> Commit 672accf1530 (include: update kernel netfilter header files)
> >> updated linux/netfilter.h and brought with it the update from kernel
> >> commit a263653ed798 (netfilter: don't pull include/linux/netfilter.h
> >> from netns headers). This triggers conflict of headers that is fixed in
> >> kernel commit 279c6c7fa64f (api: fix compatibility of linux/in.h with
> >> netinet/in.h) included in kernel version 4.2. For earlier kernel headers
> >> we need a workaround that prevents the headers conflict.
> >>
> >> Fixes the following build failure:
> >>
> >> In file included from .../sysroot/usr/include/netinet/ip.h:25:0,
> >>                  from ../include/libiptc/ipt_kernel_headers.h:8,
> >>                  from ../include/libiptc/libiptc.h:6,
> >>                  from libip4tc.c:29:
> >> .../sysroot/usr/include/linux/in.h:26:3: error: redeclaration of enumerator ‘IPPROTO_IP’
> >>    IPPROTO_IP = 0,  /* Dummy protocol for TCP  */
> >>    ^
> >> .../sysroot/usr/include/netinet/in.h:33:5: note: previous definition of ‘IPPROTO_IP’ was here
> >>      IPPROTO_IP = 0,    /* Dummy protocol for TCP.  */
> >>      ^~~~~~~~~~
> >>
> >> Cc: Florian Westphal <fw@xxxxxxxxx>
> >> Signed-off-by: Baruch Siach <baruch@xxxxxxxxxx>
> >> ---
> >>  include/linux/netfilter.h | 2 ++
> >>  1 file changed, 2 insertions(+)
> >>
> >> diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
> >> index c3f087ac680c..bacf8cd92116 100644
> >> --- a/include/linux/netfilter.h
> >> +++ b/include/linux/netfilter.h
> >> @@ -3,7 +3,9 @@
> >>
> >>  #include <linux/types.h>
> >>
> >> +#ifndef _NETINET_IN_H
> >>  #include <linux/in.h>
> >> +#endif
> >
> > This is updating a cached copy of the kernel headers, we basically
> > copy kernel headers and place in the userspace tree to make sure that
> > iptables compiles standalone, without the need for kernel-headers to
> > be installed in the system in order to simplify building process.
> >
> > I would like we don't have to modify this cached copy, so if you can
> > find a way to update the userspace C files without touching the cached
> > copy of the kernel header, that would be great. My concern is that
> > this little tweak will go away once we update the cached copy anytime
> > soon in the future.
> >
> > Thanks.
> 
> I can't think of any better solution.
> 
> A possible alternative would be to add '#define _LINUX_IN_H' in every
> file that include netinet/in.h to suppress the kernel headern. This is a
> bigger change, although is doesn't touch any cached kernel header as far
> as I can see.
> 
> Do you like this solution better?

Probably we can consolidate this in one single spot, eg.
iptables/nft.h ? So we only have to add this once.



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