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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6BD30C04AAF for ; Wed, 20 Sep 2023 16:50:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234174AbjITQuG (ORCPT ); Wed, 20 Sep 2023 12:50:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54634 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233691AbjITQuG (ORCPT ); Wed, 20 Sep 2023 12:50:06 -0400 Received: from orbyte.nwl.cc (orbyte.nwl.cc [IPv6:2001:41d0:e:133a::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5E4949F for ; Wed, 20 Sep 2023 09:50:00 -0700 (PDT) Received: from n0-1 by orbyte.nwl.cc with local (Exim 4.94.2) (envelope-from ) id 1qj0Ok-0005Cs-5f; Wed, 20 Sep 2023 18:49:58 +0200 Date: Wed, 20 Sep 2023 18:49:58 +0200 From: Phil Sutter To: Pablo Neira Ayuso Cc: Thomas Haller , NetFilter Subject: Re: [PATCH nft 3/4] all: add free_const() and use it instead of xfree() Message-ID: Mail-Followup-To: Phil Sutter , Pablo Neira Ayuso , Thomas Haller , NetFilter References: <20230920131554.204899-1-thaller@redhat.com> <20230920131554.204899-4-thaller@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org On Wed, Sep 20, 2023 at 06:06:23PM +0200, Pablo Neira Ayuso wrote: > On Wed, Sep 20, 2023 at 04:13:43PM +0200, Phil Sutter wrote: > > On Wed, Sep 20, 2023 at 03:13:40PM +0200, Thomas Haller wrote: > > [...] > > > There are many places that rightly cast away const during free. But not > > > all of them. Add a free_const() macro, which is like free(), but accepts > > > const pointers. We should always make an intentional choice whether to > > > use free() or free_const(). Having a free_const() macro makes this very > > > common choice clearer, instead of adding a (void*) cast at many places. > > > > I wonder whether pointers to allocated data should be const in the first > > place. Maybe I miss the point here? Looking at flow offload statement > > for instance, should 'table_name' not be 'char *' instead of using this > > free_const() to free it? > > The const here tells us that this string is set once and it gets never > updated again, which provides useful information when reading the > code IMO. That seems like reasonable rationale. I like to declare function arguments as const too in order to mark them as not being altered by the function. With strings, I find it odd to do: const char *buf = strdup("foo"); free((void *)buf); > I interpret from Phil's words that it would be better to consolidate > this to have one single free call, in that direction, I agree. No, I was just wondering why we have this need for free_const() in the first place (i.e., why we declare pointers as const if we allocate/free them). > /* Just free(), but casts to a (void*). This is for places where > * we have a const pointer that we know we want to free. We could just > * do the (void*) cast, but free_const() makes it clear that this is > * something we frequently need to do and it's intentional. */ > #define free_const(ptr) free((void *)(ptr)) > > I like this macro. > > Maybe turn it into: > > nft_free(ptr) > > and we use it everywhere? I believe this is exactly what Thomas is trying to move away from. IIUC, he wants to have a "special" free() to mark the spots where a const pointer is freed (and make it a more deliberate action). Cheers, Phil