[Buildroot] [PATCH v1] libv4l: add missing bpf_common.h header

[Peter Seiderer <ps.report@gmx.net>]

Hello Fabrice,

On Wed, 7 Nov 2018 20:05:51 +0100, Fabrice Fontaine <fontaine.fabrice@gmail.com> wrote:

> Dear Peter,
> Le mer. 7 nov. 2018 ? 17:59, Peter Korsgaard <peter@korsgaard.com> a ?crit :
> >  
> > >>>>> "Fabrice" == Fabrice Fontaine <fontaine.fabrice@gmail.com> writes:  
> >
> > Hi,
> >  
> >  > Thanks for submitting this patch however build failures remain on some
> >  > architectures (ARM cortex a8 / a9 / arm926ej-s) with "old" kernel
> >  > headers (3.13) :
> >  > - http://autobuild.buildroot.org/results/b48/b48f9b284102d94b847a35ed1ca50a157fbcb1c9/build-end.log
> >  > - http://autobuild.buildroot.org/results/339/3391705aca7022111ef743212b7cad57f0cdea9a/build-end.log  
> >  
> >  > Build failures are raised because _NR_bpf is not defined:  
> >  
> >  > bpf.c:48:4: error: #error __NR_bpf not defined. libbpf does not
> >  > support your arch.
> >  >  #  error __NR_bpf not defined. libbpf does not support your arch.  
> >  
> >  > From my understanding, __NR_bpf should be normally defined by the
> >  > kernel (when it is not too old).
> >  > For example, __NR_bpf has been defined for m68k and powerpc since 3.18:
> >  > - https://github.com/torvalds/linux/commit/f7bbd12a4b7e088f53f20dd31019984459699fb9
> >  > - https://github.com/torvalds/linux/commit/fcbb539f279f7d854bd49819b889fea0612909f8
> >  > The code in bpf.c only defines fallback for very few few
> >  > architectures: i386, x86_64, aarch64, sparc and s390.  
> >
> > But the fallback only fixes setups with older kernel headers than the
> > runtime kernel, which is IMHO fairly rare in Buildroot - Unless the tool
> > works correctly when the bpf syscall fails.
> >  
> >  > So finally, should we add a dependency on
> >  > BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_18 on a new
> >  > BR2_PACKAGE_LIBV4L_KEYTABLE_BPF_PROTOCOLS option?  
> >
> > The BPF_PROTOCOLS conditional seems to be about using clang to compile
> > bdf byte code, which is not directly the code that is failing here.
> >
> > If it is easy to disable bpf support completely, then that is probably
> > the nicest solution, otherwise I am fine with depending on 3.18, that is
> > after all almost 4 years old by now.  
> Thanks for your feedback, I will add a --without-libelf option to configure.ac.

No libelf is not enough for disabling bpf, see the autobuild failure [1]:

[...]
checking for LIBELF... no
configure: WARNING: libelf library not available
[...]
In file included from bpf.h:26:0,
                 from keytable.c:37:
../../include/linux/bpf.h:12:30: fatal error: linux/bpf_common.h: No such file or directory
 #include <linux/bpf_common.h>
                              ^

Maybe take a look at the upstream efforts:

[PATCH v2 v4l-utils] configure: build without BPF support in ir-keytable
https://patchwork.linuxtv.org/patch/52841/

Regards,
Peter

[1] http://autobuild.buildroot.org/results/d22c0939eed4bc949f7eaeae7595d01ec45cc2cd/build-end.log

> >
> > --
> > Bye, Peter Korsgaard  
> Best Regards,
> 
> Fabrice