linux-kernel - Re: [PATCH v8 net-next 2/2] net: filter: split filter.h and expose eBPF to user space

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Date:	Sat, 30 Aug 2014 00:24:32 +0200
From:	Daniel Borkmann <dborkman@...hat.com>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:	Alexei Starovoitov <ast@...mgrid.com>,
	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Namhyung Kim <namhyung@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Linux API <linux-api@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 net-next 2/2] net: filter: split filter.h and expose
 eBPF to user space

On 08/29/2014 08:02 PM, Alexei Starovoitov wrote:
> On Fri, Aug 29, 2014 at 10:39 AM, Daniel Borkmann <dborkman@...hat.com> wrote:
>> On 08/27/2014 10:37 PM, Alexei Starovoitov wrote:
>>>
>>> allow user space to generate eBPF programs
>>>
>>> uapi/linux/bpf.h: eBPF instruction set definition
>>>
>>> linux/filter.h: the rest
>>
>> Very sorry for being late, but just a thought since we're touching user
>> space headers anyway ...
>>
>> Wouldn't it be more consistent to have it organized as follows ...
>>
>>   - uapi/linux/bpf.h    : classic BPF instruction set parts only
>>   - uapi/linux/ebpf.h   : eBPF instruction set definition (which also
>>                           includes uapi/linux/bpf.h though)
>> ... and have ...
>>
>>   - uapi/linux/filter.h : just include uapi/linux/bpf.h but rest is empty
>>
>> That way, it would be more consistent ...
>>
>> Old legacy application can stay with linux/filter.h; new applications
>> based on their needs can choose between linux/{e,}bpf.h and in the kernel,
>> we can just include linux/ebpf.h.
>>
>> Right now, it seems, an eBPF user space program would need to include
>> 2 header files in user space (linux/filter.h, linux/bpf.h) which I find
>> a bit confusing.
>
> It's been bugging me as well, but I suspect having it the way you
> described won't work. Mainly because we cannot do include <uapi/..>
> inside uapi/*.h, so we would need to do include <linux/bpf.h>
> inside uapi/linux/filter.h, but that will cause serious include path
> confusion. That was the reason I didn't simply do include <linux/filter.h>
> inside uapi/linux/bpf.h
>
> Also I really dislike 'ebpf' name in all lower case. If we make such header
> file name, we would need to rename all macros and function names
> to EBPF_... which I find very ugly looking. I think all good abbreviations are
> three letters :)

I don't think we would have to name defines that way, really, that would be
terrible. We can keep them simply *as is*. Not sure though why bpf.h + ebpf.h
would be that bad. ;) I haven't tried it out yet, but if we would indeed run
into a name collision, above proposal would resolve that.
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