From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0A0D3C4363C for ; Sun, 4 Oct 2020 14:53:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B8BD4206B6 for ; Sun, 4 Oct 2020 14:53:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725830AbgJDOxp (ORCPT ); Sun, 4 Oct 2020 10:53:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47938 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725825AbgJDOxp (ORCPT ); Sun, 4 Oct 2020 10:53:45 -0400 Received: from orbyte.nwl.cc (orbyte.nwl.cc [IPv6:2001:41d0:e:133a::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C2ACEC0613CE for ; Sun, 4 Oct 2020 07:53:44 -0700 (PDT) Received: from n0-1 by orbyte.nwl.cc with local (Exim 4.94) (envelope-from ) id 1kP5ON-0005pW-QF; Sun, 04 Oct 2020 16:53:39 +0200 Date: Sun, 4 Oct 2020 16:53:39 +0200 From: Phil Sutter To: Pablo Neira Ayuso Cc: netfilter-devel@vger.kernel.org, Serhey Popovych Subject: Re: [iptables PATCH 1/3] libxtables: Make sure extensions register in revision order Message-ID: <20201004145339.GE29050@orbyte.nwl.cc> Mail-Followup-To: Phil Sutter , Pablo Neira Ayuso , netfilter-devel@vger.kernel.org, Serhey Popovych References: <20200922225341.8976-1-phil@nwl.cc> <20200922225341.8976-2-phil@nwl.cc> <20201003111741.GA3035@salvia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201003111741.GA3035@salvia> Sender: Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org Hi Pablo, On Sat, Oct 03, 2020 at 01:17:41PM +0200, Pablo Neira Ayuso wrote: > On Wed, Sep 23, 2020 at 12:53:39AM +0200, Phil Sutter wrote: > > Insert extensions into pending lists in ordered fashion: Group by > > extension name (and, for matches, family) and order groups by descending > > revision number. > > > > This allows to simplify the later full registration considerably. Since > > that involves kernel compatibility checks, the extra cycles here pay off > > eventually. > > > > Signed-off-by: Phil Sutter > > --- > > libxtables/xtables.c | 64 +++++++++++++++++++++++++++++++++++++++----- > > 1 file changed, 58 insertions(+), 6 deletions(-) > > > > diff --git a/libxtables/xtables.c b/libxtables/xtables.c > > index 8907ba2069be7..63d0ea5def2d5 100644 > > --- a/libxtables/xtables.c > > +++ b/libxtables/xtables.c > > @@ -948,8 +948,14 @@ static void xtables_check_options(const char *name, const struct option *opt) > > } > > } > > > > +static int xtables_match_prefer(const struct xtables_match *a, > > + const struct xtables_match *b); > > + > > void xtables_register_match(struct xtables_match *me) > > { > > + struct xtables_match **pos; > > + bool seen_myself = false; > > + > > if (me->next) { > > fprintf(stderr, "%s: match \"%s\" already registered\n", > > xt_params->program_name, me->name); > > @@ -1001,10 +1007,32 @@ void xtables_register_match(struct xtables_match *me) > > if (me->extra_opts != NULL) > > xtables_check_options(me->name, me->extra_opts); > > > > + /* order into linked list of matches pending full registration */ > > + for (pos = &xtables_pending_matches; *pos; pos = &(*pos)->next) { > > + /* NOTE: No extension_cmp() here as we accept all families */ > > + if (strcmp(me->name, (*pos)->name) || > > + me->family != (*pos)->family) { > > + if (seen_myself) > > + break; > > + continue; > > + } > > + seen_myself = true; > > + if (xtables_match_prefer(me, *pos) >= 0) > > xtables_match_prefer() evaluates >= 0 if 'me' has higher revision > number than *pos. So list order is: higher revision first. Correct. > > + break; > > + } > > + if (!*pos) > > + pos = &xtables_pending_matches; > > > > - /* place on linked list of matches pending full registration */ > > - me->next = xtables_pending_matches; > > - xtables_pending_matches = me; > > + me->next = *pos; > > This line above is placing 'me' right before the existing match in the list. Also correct. As stated in the description, xtables_pending_matches should be grouped by name and family and within those groups ordered by descending revision. > > + *pos = me; > > This line above only works if *pos is &xtables_pending_matches? This piece of code confused me at first, too. I even wrote a quick test to make sure the pointer stuff works as intended. :D In fact, *pos can't be &xtables_pending_matches: pos is type 'struct xtables_match **' (note the double pointer). pos is either &xtables_pending_matches or the address of the right position's previous element's 'next' pointer. Still confusing, but the for-loop is clear: | for (pos = &xtables_pending_matches; *pos; pos = &(*pos)->next) { So by doing '*pos = me', the 'next' pointer value is changed (or the value of xtables_pending_matches. > Looking at the in-tree extensions, they are always ordered from lower > to higher (in array definitions). This is in favor of the sorting algorithm: Inserting revision N+1 will find revision N first in its group if revisions 0..N were inserted before. So having extension revisions ordered ascending in their array is optimal. Cheers, Phil