Subject: Re: [PATCH v5 tip 1/7] bpf: make internal bpf API independent of CONFIG_BPF_SYSCALL ifdefs

From: Masami Hiramatsu <[email-masked]>
Date: Mon, 02 Mar 2015 20:51:31 +0900

(2015/03/02 20:10), Daniel Borkmann wrote:
> On 03/02/2015 11:53 AM, Masami Hiramatsu wrote:
> ...
>> Hmm, it seems that this still doesn't hide some APIs which is provided
>> only when CONFIG_BPF_SYSCALL. For example bpf_register_map_type etc.
>> I think all those APIs should be hidden in #ifdef or at least be commented
>> so that the user doesn't refer that without the kconfig.
>> (I don't think we need to provide dummy functions for those APIs,
>>   but it's better to clarify which API we can use with which kconfig)
> 
> Well, currently all possible map types (hash table, array map) that
> would actually call into bpf_register_map_type() are only built when
> CONFIG_BPF_SYSCALL is enabled (see kernel/bpf/Makefile). I don't think
> new map additions should be added that are not under kernel/bpf/ and/or
> enabled outside the CONFIG_BPF_SYSCALL, as it should be considered
> part of the eBPF core code.
> 
> The difference here (this patch) is simply that we don't want users to
> build ifdef spaghetti constructs in user code, so the API that is
> actually used by eBPF _users_ is being properly ifdef'ed in the headers.
> 
> So, I don't think this is a big problem, but we could move these bits
> under the ifdef CONFIG_BPF_SYSCALL w/o providing a dummy in the else part.
> I can do that outside of the scope of this set.

Or, maybe we'd better move them into new include/linux/bpf_prog.h which
includes basic include/linux/bpf.h. Then, user can include the bpf_prog.h
instead of bpf.h. Also, we can check CONFIG_BPF_SYSCAL=y at the top of
bpf_prog.h. This makes things clearer :)

Thank you,

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: [email-masked]