Subject: Re: linux-next: build failure after merge of the net tree

From: Ingo Molnar <[email-masked]>
Date: Tue, 14 Feb 2017 07:42:21 +0100

* Stephen Rothwell <[email-masked]> wrote:

> Hi all,
> 
> After merging the net tree, today's linux-next build (powerpc64le perf)
> failed like this:
> 
> Warning: tools/include/uapi/linux/bpf.h differs from kernel
> bpf.c: In function 'bpf_prog_attach':
> bpf.c:180:6: error: 'union bpf_attr' has no member named 'attach_flags'; did you mean 'map_flags'?
>   attr.attach_flags  = flags;
>       ^
> 
> Caused by commit
> 
>   7f677633379b ("bpf: introduce BPF_F_ALLOW_OVERRIDE flag")
> 
> Unfortunately, the perf header files are kept separate from the kernel
> header files proper and are not automatically copied over :-(

No, that's wrong, the problem is not that headers were not shared, the problem is 
that a tooling interdependency was not properly tested *and* that the dependency 
was not properly implemented in the build system either.

Note that we had similar build breakages when include headers _were_ shared as 
well, so sharing the headers would only have worked around this particular bug and 
would have introduced fragility in other places...

The best, most robust solution in this particular case would be to fix the 
(tooling) build system to express the dependency, that would have shown the build 
failure right when the modification was done.

Thanks,

	Ingo