Re: [PATCH v6 net-next 4/6] bpf: enable bpf syscall on x64 and i386

[Alexei Starovoitov]

On Mon, Aug 25, 2014 at 6:07 PM, David Miller <davem@xxxxxxxxxxxxx> wrote:
> From: Alexei Starovoitov <ast@xxxxxxxxxxxx>
> 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/