netdev - Re: [PATCH iproute2 master] bpf: provide fallback defs for __NR

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Date:   Thu, 15 Jun 2017 01:01:14 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Stephen Hemminger <stephen@...workplumber.org>
CC:     alexei.starovoitov@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH iproute2 master] bpf: provide fallback defs for __NR_bpf
 when not avail

On 06/15/2017 12:56 AM, Stephen Hemminger wrote:
> On Thu, 15 Jun 2017 00:47:15 +0200
> Daniel Borkmann <daniel@...earbox.net> wrote:
>
>> panji reported that he wasn't able to build iproute2's bpf library
>> due to lack of __NR_bpf in his system headers. Providing a fallback
>> definition when __NR_bpf is not available in the system lets the
>> loader compile just fine, so lets add them for majority of archs.
>>
>> Reported-by: panji <jpan@...e.nl>
>> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
>> ---
>>   lib/bpf.c | 20 ++++++++++++++++++++
>>   1 file changed, 20 insertions(+)
>>
>> diff --git a/lib/bpf.c b/lib/bpf.c
>> index ae4d97d..e1e29cc 100644
>> --- a/lib/bpf.c
>> +++ b/lib/bpf.c
>> @@ -128,6 +128,26 @@ static inline __u64 bpf_ptr_to_u64(const void *ptr)
>>   	return (__u64)(unsigned long)ptr;
>>   }
>>
>> +#ifndef __NR_bpf
>> +# if defined(__i386__)
>> +#  define __NR_bpf 357
>> +# elif defined(__x86_64__)
>> +#  define __NR_bpf 321
>> +# elif defined(__aarch64__)
>> +#  define __NR_bpf 280
>> +# elif defined(__sparc__)
>> +#  define __NR_bpf 349
>> +# elif defined(__arm__)
>> +#  define __NR_bpf 386
>> +# elif defined(__powerpc__)
>> +#  define __NR_bpf 361
>> +# elif defined(__s390__)
>> +#  define __NR_bpf 351
>> +# else
>> +#  error __NR_bpf not defined. Update kernel headers.
>> +# endif
>> +#endif
>> +
>>   static int bpf(int cmd, union bpf_attr *attr, unsigned int size)
>>   {
>>   #ifdef __NR_bpf
>
> Sorry this looks like a mess. enumerating architectures in two different
> projects is likely to break in future.

It says ifndef __NR_bpf, so only used then. And the numbers are uabi,
what will break here exactly? libbpf in kernel tree is having a similar
approach by the way.