linux-kernel - Re: [PATCH v12 net-next 03/11] bpf: add lookup/update/delete/iterate methods to BPF maps

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Message-ID: <CAMEtUuzy0Hvjr0f4XBrH+FAxaKD7aijnYzDe3-MPrGWe6+MD4Q@mail.gmail.com>
Date:	Tue, 16 Sep 2014 14:23:27 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	David Miller <davem@...emloft.net>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Daniel Borkmann <dborkman@...hat.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Pablo Neira Ayuso <pablo@...filter.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>,
	Network Development <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 net-next 03/11] bpf: add lookup/update/delete/iterate
 methods to BPF maps

On Tue, Sep 16, 2014 at 1:54 PM, David Miller <davem@...emloft.net> wrote:
>
> The cost of the compat layer must be considered and weighted
> against this cast, which I think is really no big deal.
>
>> I think compat layer is a better option.
>
> It's overhead you'll have to support forever, I think you should
> reconsider.
>
> All of the "ugly casting" will be hidden, or can be hidden, in the
> syscall wrappers and/or interfaces in userspace.

ahh, ok. I thought you're strongly against any type of casts.
In such case I can get rid of 'union bpf_attr' as well and simply
define a struct per command, then syscall will look like:
sys_bpf(int cmd, void __user *attr, unsigned int size);
and uapi/linux/bpf.h will have:
struct bpf_prog_load_attr { /* for BPF_PROG_LOAD cmd */
    __u32 prog_type;
    __u32 insn_cnt;
    __aligned_u64 insns;
    __aligned_u64 license;
    __u32 log_level;
    __u32 log_size;
    __aligned_u64 log_buf;
};
and similar for other commands.
no compat layer and type checking will be done
by syscall wrappers. Ok?
--
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