From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760920AbaGYSvJ (ORCPT ); Fri, 25 Jul 2014 14:51:09 -0400 Received: from mail-vc0-f177.google.com ([209.85.220.177]:65105 "EHLO mail-vc0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760737AbaGYSvE (ORCPT ); Fri, 25 Jul 2014 14:51:04 -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> From: Willem de Bruijn Date: Fri, 25 Jul 2014 14:50:32 -0400 Message-ID: Subject: Re: [PATCH net-next] net: filter: rename 'struct sk_filter' to 'struct bpf_prog' To: Alexei Starovoitov 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 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.