Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760857AbaGYTCP (ORCPT ); Fri, 25 Jul 2014 15:02:15 -0400 Received: from mail-wi0-f181.google.com ([209.85.212.181]:62953 "EHLO mail-wi0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753299AbaGYTCN (ORCPT ); Fri, 25 Jul 2014 15:02:13 -0400 MIME-Version: 1.0 In-Reply-To: References: <1406275499-7822-1-git-send-email-ast@plumgrid.com> <53D23EAF.4000001@redhat.com> <20140725115414.GA4770@salvia> Date: Fri, 25 Jul 2014 12:02:11 -0700 Message-ID: Subject: Re: [PATCH net-next] net: filter: rename 'struct sk_filter' to 'struct bpf_prog' From: Alexei Starovoitov To: Willem de Bruijn Cc: Pablo Neira Ayuso , Daniel Borkmann , "David S. Miller" , Network Development , linux-kernel , netfilter-devel Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 25, 2014 at 11:58 AM, Alexei Starovoitov wrote: > On Fri, Jul 25, 2014 at 11:50 AM, Willem de Bruijn wrote: >> On Fri, Jul 25, 2014 at 2:43 PM, Alexei Starovoitov wrote: >>> On Fri, Jul 25, 2014 at 11:32 AM, Willem de Bruijn wrote: >>>>>> This follows a convention in include/uapi/linux/netfilter/*.h that >>>>>> likely predates the introduction of uapi. A search for "Used >>>>>> internally by the kernel" shows many more examples. I should not have >>>>>> included filter.h, however. The common behavior when using pointers >>>>>> to kernel-internal structures is to have a forward declaration. I suggest >>>>>> making that change, instead of changing to void *. This avoids having >>>>>> to add casts where xt_bpf_info is used in net/netfilter/xt_bpf.c: >>>>> >>>>> that will not avoid typecast. >>>>> Either 'void *' approach or extra 'struct sk_filter;' approach, both need >>>>> type casts to 'struct bpf_prog' in xt_bpf.c >>>>> (because of SK_RUN_FILTER macro) >>>>> Therefore I prefer extra 'struct sk_filter;' approach. >>>> >>>> I hadn't noticed that your patch makes the same change that I >>>> proposed. Nothing in userspace should touch that pointer, so it is >>>> fine to change its type to struct bpf_prog* at the same time. No need >>>> for typecasts. >>> >>> really? I don't think it's a good idea to expose kernel struct type >>> to user space. How is it even going to compile? >> >> a forward declaration. >> >>> #include brings different files in kernel and in user space. >>> struct bpf_prog is undefined in user space and compiler will complain. >>> Adding 'struct bpf_prog;' will be ugly. >>> imo the lesser evil is adding 'struct sk_filter;' and doing type casts >>> in kernel. >> >> but the exact same argument applies to sk_filter. If that struct is >> renamed everywhere else, then the result will only be more confusing. >> A forward declaration is the standard workaround to all such cases in >> include/uapi/linux/netfilter. See for instance xt_connlimit.h. This is >> sufficient to allow userspace build to succeed, without exposing any >> kernel structure detail. If you don't even want to leak the name, then >> let's make it void *. Keeping a declaration for sk_filter, while >> sk_filter is renamed everywhere else is the least good option, in my >> opinion. > > well, since you the author of this bit and you're ok with 'void *', I'm ok > with it too :) Just typecast in kernel is still needed because of > SK_RUN_FILTER() macro... just tried with 'void *', actually all three type casts are needed... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/