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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7955EC433F5 for ; Thu, 30 Sep 2021 14:06:35 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E9F3860ED6 for ; Thu, 30 Sep 2021 14:06:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org E9F3860ED6 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:51544 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mVwhm-0003yL-7t for qemu-devel@archiver.kernel.org; Thu, 30 Sep 2021 10:06:34 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:43070) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mVwdZ-00016E-U0 for qemu-devel@nongnu.org; Thu, 30 Sep 2021 10:02:13 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:23058) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mVwdV-0003xx-PZ for qemu-devel@nongnu.org; Thu, 30 Sep 2021 10:02:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633010527; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ok8331cXZuaIDU4yRXEbjL/pkkhxrYJlIUZC3yiRlzA=; b=et9/P4+522/+3PUQGWel0FhjUk1kmFQpgi3HPgmba9ngp7mcmOO80OkhHhOkwo9+mgzycG e+SxGuaDHnWoqUlRu1NML70yTNNZBtM+YN4VKoM4KEGKaeL8rC78bQhaFEoQIGwvh3+Lyx hSgiWhzPFofKzN2qK2/2dczTPoS7ryk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-126-lWWZ-7cLNdWL8qh2dojmcw-1; Thu, 30 Sep 2021 10:01:55 -0400 X-MC-Unique: lWWZ-7cLNdWL8qh2dojmcw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BE8DF18125DB; Thu, 30 Sep 2021 14:01:42 +0000 (UTC) Received: from redhat.com (unknown [10.39.195.104]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 80B0F652A4; Thu, 30 Sep 2021 14:01:41 +0000 (UTC) Date: Thu, 30 Sep 2021 15:01:38 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Christian Schoenebeck Subject: Re: [PATCH v2 1/5] qemu/qarray.h: introduce QArray Message-ID: References: <12467459.urXsdUxXdL@silver> <4707830.eRlNOxMu1p@silver> MIME-Version: 1.0 In-Reply-To: <4707830.eRlNOxMu1p@silver> User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Alex =?utf-8?Q?Benn=C3=A9e?= , Richard Henderson , qemu-devel@nongnu.org, Greg Kurz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Sep 30, 2021 at 03:55:36PM +0200, Christian Schoenebeck wrote: > On Donnerstag, 30. September 2021 15:31:10 CEST Daniel P. Berrangé wrote: > > On Thu, Sep 30, 2021 at 03:20:19PM +0200, Christian Schoenebeck wrote: > > > On Mittwoch, 29. September 2021 19:48:38 CEST Daniel P. Berrangé wrote: > > > > On Wed, Sep 29, 2021 at 07:32:39PM +0200, Christian Schoenebeck wrote: > > > > > On Dienstag, 28. September 2021 18:41:17 CEST Daniel P. Berrangé > wrote: > > > > > > On Tue, Sep 28, 2021 at 06:23:23PM +0200, Christian Schoenebeck > wrote: > > > > > > > On Dienstag, 28. September 2021 15:04:36 CEST Daniel P. Berrangé > > > > > > wrote: > > > > > > > > On Sun, Aug 22, 2021 at 03:16:46PM +0200, Christian Schoenebeck > > > > > > wrote: > > > > > [...] > > > > > > > > > > > The GLib automatic memory support is explicitly designed to be > > > > > > extendd > > > > > > with support for application specific types. We already do exactly > > > > > > that > > > > > > all over QEMU with many calls to G_DEFINE_AUTOPTR_CLEANUP_FUNC(..) > > > > > > to > > > > > > register functions for free'ing specific types, such that you can > > > > > > use 'g_autoptr' with them. > > > > > > > > > > Ok, just to make sure that I am not missing something here, because > > > > > really > > > > > if there is already something that does the job that I simply haven't > > > > > seen, then I happily drop this QArray code. > > > > > > > > I don't believe there is anything that currently addresses this well. > > > > > > > > > But AFAICS this G_DEFINE_AUTOPTR_CLEANUP_FUNC() & g_autoptr concept > > > > > does > > > > > not have any notion of "size" or "amount", right? > > > > > > > > Correct, all it knows is that there's a data type and an associated > > > > free function. > > > > > > Ok, thanks for the clarification. > > > > > > > > So let's say you already have the following type and cleanup function > > > > > in > > > > > your existing code: > > > > > > > > > > typedef struct MyScalar { > > > > > > > > > > int a; > > > > > char *b; > > > > > > > > > > } MyScalar; > > > > > > > > > > void myscalar_free(MayScalar *s) { > > > > > > > > > > g_free(s->b); > > > > > > > > > > } > > > > > > > > > > Then if you want to use G_DEFINE_AUTOPTR_CLEANUP_FUNC() for an array > > > > > on > > > > > that scalar type, then you still would need to *manually* write > > > > > additionally a separate type and cleanup function like: > > > > > > > > > > typedef struct MyArray { > > > > > > > > > > MyScalar *s; > > > > > int n; > > > > > > > > > > }; > > > > > > > > > > void myarray_free(MyArray *a) { > > > > > > > > > > for (int i = 0; i < a->n; ++i) { > > > > > > > > > > myscalar_free(a->s[i]); > > > > > > > > > > } > > > > > g_free(a); > > > > > > > > > > } > > > > > > > > > > Plus you have to manually populate that field 'n' after allocation. > > > > > > > > > > Am I wrong? > > > > > > > > Yes and no. You can of course manually write all these stuff > > > > as you describe, but since we expect the array wrappers to be > > > > needed for more than one type it makes more sense to have > > > > that all done via macros. > > > > > > > > Your patch contains a DECLARE_QARRAY_TYPE and DEFINE_QARRAY_TYPE > > > > that provide all this reqiured boilerplate code. The essential > > > > difference that I'm suggesting is that the array struct type emitted > > > > by the macro is explicitly visible as a concept to calling code such > > > > that it is used directly used with g_autoptr. > > > > > > I got that, but your preferred user pattern was this: > > > DECLARE_QARRAY_TYPE(Foo); > > > > > > ... > > > > > > g_autoptr(FooArray) foos = foo_array_new(n); > > > > > > I don't see a portable way to do upper-case to lower-case conversion with > > > the> > > > C preprocessor. So you would end up like this instead: > > > g_autoptr(FooArray) foos = Foo_array_new(n); > > > > > > Which does not really fit into common QEMU naming conventions either, does > > > it? > > Right, it would need to be a two arg macro: > > > > DECLARE_QARRAY_TYPE(Foo, foo); > > > > similar to what we do with macros for declaring QOM types becuase of > > the same case conversion needs. > > > > > And I can help it, I don't see what's wrong in exposing a regular C-array > > > to user code. I mean in the Linux kernel for instance it is absolutely > > > normal to convert from a compound structure to its parent structure. I > > > don't find anything magical about that and it is simply less code and > > > better readable. > > QEMU code is not Linux code. We're following the GLib practices for > > automatic memory deallocation, and QOM is also modelled on GLib. The > > proposal looks magical from the POV of QEMU's code patterns, as it is > > not making use of GLib's g_auto* code. > > Hmm, I start to think whether I should just make it some 9p local utility code > for now instead, e.g. "P9Array" or something. IMHO even if it was private to a subsystem it should still be using the standard g_auto functionality for automatically deallocating memory, because this is a QEMU wide standard. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|