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

From: Alexei Starovoitov
Date: Fri Aug 29 2014 - 14:03:06 EST

On Fri, Aug 29, 2014 at 10:39 AM, Daniel Borkmann <dborkman@xxxxxxxxxx> 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 :)
So I very much prefer bpf.h as a main file name.
Later we can move some of old classic BPF defines into
uapi/linux/bpf_common.h and then include it in both uapi/linux/bpf.h
and in uapi/linux/filter.h, then the nuisance of two include files for
user space will go away. Classic users will keep using linux/filter.h
and new apps will include linux/bpf.h only.
I think we should probably do such header optimization later and very carefully.
I'm a bit afraid to touch uapi/linux/filter.h since it's used in so
many user apps.
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