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Date:	Mon, 25 Aug 2014 18:43:55 -0700
From:	Alexei Starovoitov <>
To:	David Miller <>
Cc:	Ingo Molnar <>,
	Linus Torvalds <>,
	Andy Lutomirski <>,
	Steven Rostedt <>,
	Daniel Borkmann <>,
	Chema Gonzalez <>,
	Eric Dumazet <>,
	Peter Zijlstra <>,
	Brendan Gregg <>,
	Namhyung Kim <>,
	"H. Peter Anvin" <>,
	Andrew Morton <>,
	Kees Cook <>,
	Linux API <>,
	Network Development <>,
	LKML <>
Subject: Re: [PATCH v6 net-next 4/6] bpf: enable bpf syscall on x64 and i386

On Mon, Aug 25, 2014 at 6:07 PM, David Miller <> wrote:
> From: Alexei Starovoitov <>
> Date: Mon, 25 Aug 2014 18:00:56 -0700
>> -
>> +asmlinkage long sys_bpf(int cmd, unsigned long arg2, unsigned long arg3,
>> +                     unsigned long arg4, unsigned long arg5);
> Please do not add interfaces with opaque types as arguments.
> It is impossible for the compiler to type check the args at
> compile time when userspace tries to use this stuff.

I share this concern. I went with single BPF syscall, because
alternative is 6 syscalls for every command and more
syscalls in the future when we'd need to add another command.
I think type casting is much lesser evil.
We already have similar muxing syscalls.
It feels to me that single mux/demux syscall is easier to support,
document, add new commands. Type casting, yeah, not pretty.
Most users will be using wrappers similar to those I've defined in libbpf.h
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