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=-11.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 63B24C4363A for ; Mon, 5 Oct 2020 22:43:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 31A23206C3 for ; Mon, 5 Oct 2020 22:43:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726712AbgJEWnB (ORCPT ); Mon, 5 Oct 2020 18:43:01 -0400 Received: from correo.us.es ([193.147.175.20]:48946 "EHLO mail.us.es" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725846AbgJEWnA (ORCPT ); Mon, 5 Oct 2020 18:43:00 -0400 Received: from antivirus1-rhel7.int (unknown [192.168.2.11]) by mail.us.es (Postfix) with ESMTP id 5F4A2D28C4 for ; Tue, 6 Oct 2020 00:42:58 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id 4ED6CDA73F for ; Tue, 6 Oct 2020 00:42:58 +0200 (CEST) Received: by antivirus1-rhel7.int (Postfix, from userid 99) id 44596DA722; Tue, 6 Oct 2020 00:42:58 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id E586EDA704; Tue, 6 Oct 2020 00:42:55 +0200 (CEST) Received: from 192.168.1.97 (192.168.1.97) by antivirus1-rhel7.int (F-Secure/fsigk_smtp/550/antivirus1-rhel7.int); Tue, 06 Oct 2020 00:42:55 +0200 (CEST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/antivirus1-rhel7.int) Received: from us.es (unknown [90.77.255.23]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: 1984lsi) by entrada.int (Postfix) with ESMTPSA id CA5A142EF42A; Tue, 6 Oct 2020 00:42:55 +0200 (CEST) Date: Tue, 6 Oct 2020 00:42:55 +0200 X-SMTPAUTHUS: auth mail.us.es From: Pablo Neira Ayuso To: Phil Sutter , netfilter-devel@vger.kernel.org, Serhey Popovych Subject: Re: [iptables PATCH 1/3] libxtables: Make sure extensions register in revision order Message-ID: <20201005224255.GA13440@salvia> References: <20200922225341.8976-1-phil@nwl.cc> <20200922225341.8976-2-phil@nwl.cc> <20201003111741.GA3035@salvia> <20201004145339.GE29050@orbyte.nwl.cc> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20201004145339.GE29050@orbyte.nwl.cc> User-Agent: Mutt/1.10.1 (2018-07-13) X-Virus-Scanned: ClamAV using ClamSMTP Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org On Sun, Oct 04, 2020 at 04:53:39PM +0200, Phil Sutter wrote: > 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. pos is always &xtables_pending_matches: - The first element in the array finds no matching, then: if (!*pos) pos = &xtables_pending_matches; kicks in and and pos is set to &xtables_pending_matches, so this is inserted in the first position of the xtables_pending_matches. - The follow up element in the array (higher revision) finds itself at the very beginning of the iteration, so pos here is &xtables_pending_matches too. So *pos = me; is always updating the next pointer in the xtables_pending_matches. Same picture you're describing? I just found a bit confusing that this is using *pos = me to refresh xtables_pending_matches, probably you can just use xtables_pending_matches = me; I would add a bug check somewhere too in case that an extension is not inserted in the first position, *pos = me won't work in that case. May I suggest you please extend the commit message a bit to describe this logic? > > 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. This is optimizing userspace for more recent kernels, that sounds reasonable.