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 [off-list ref] wrote:

From: Alexei Starovoitov <ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
Date: Mon, 25 Aug 2014 18:00:56 -0700

quoted

-
+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