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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 8E575C54EE9 for ; Fri, 16 Sep 2022 08:55:17 +0000 (UTC) Received: from localhost ([::1]:38472 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oZ780-00027B-KW for qemu-devel@archiver.kernel.org; Fri, 16 Sep 2022 04:55:16 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:36366) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oZ73i-0007bg-FR for qemu-devel@nongnu.org; Fri, 16 Sep 2022 04:50:53 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:51162) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oZ73e-0005TD-2L for qemu-devel@nongnu.org; Fri, 16 Sep 2022 04:50:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1663318244; 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=YGitLjlR1zU87E/5Yx/kk39s3cPloCPj6c/iW0HIMWY=; b=iqvXE+rxKTwQZtMXy/DDRi9EsBw1WCt6nXpjw3+BmOlZTVmyirt2s+4mYmuMsKX8u8WH9/ 1LzT0VK4jdDR/gmBPNbjyh3PvzezXNFg/93aTHCPrsAs2nbL8TcGP/ptLwPz4PM1nWt2DI vBrjYyBSfD7TTzdvL2YArurSCmMMTvU= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-534-kOWrCe_0OuuduiYCRaw5GQ-1; Fri, 16 Sep 2022 04:50:41 -0400 X-MC-Unique: kOWrCe_0OuuduiYCRaw5GQ-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id BCD1F101A528; Fri, 16 Sep 2022 08:50:40 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.55]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CAEED492CA2; Fri, 16 Sep 2022 08:50:39 +0000 (UTC) Date: Fri, 16 Sep 2022 09:50:37 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Cc: qemu-devel@nongnu.org, michael.roth@amd.com, jsnow@redhat.com, eblake@redhat.com Subject: Re: [PATCH 04/27] qapi: Start to elide redundant has_FOO in generated C Message-ID: References: <20220915204317.3766007-1-armbru@redhat.com> <20220915204317.3766007-5-armbru@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220915204317.3766007-5-armbru@redhat.com> User-Agent: Mutt/2.2.6 (2022-06-05) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 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, 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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Sep 15, 2022 at 10:42:54PM +0200, Markus Armbruster wrote: > In QAPI, absent optional members are distinct from any present value. > We thus represent an optional schema member FOO as two C members: a > FOO with the member's type, and a bool has_FOO. Likewise for function > arguments. > > However, has_FOO is actually redundant for a pointer-valued FOO, which > can be null only when has_FOO is false, i.e. has_FOO == !!FOO. Except > for arrays, where we a null FOO can also be a present empty array. > > The redundant has_FOO are a nuisance to work with. Improve the > generator to elide them. Uses of has_FOO need to be replaced as > follows. > > Tests of has_FOO become the equivalent comparison of FOO with null. > For brevity, this is commonly done by implicit conversion to bool. > > Assignments to has_FOO get dropped. > > Likewise for arguments to has_FOO parameters. > > Beware: code may violate the invariant has_FOO == !!FOO before the > transformation, and get away with it. The above transformation can > then break things. Two cases: > > * Absent: if code ignores FOO entirely when !has_FOO (except for > freeing it if necessary), even non-null / uninitialized FOO works. > Such code is known to exist. > > * Present: if code ignores FOO entirely when has_FOO, even null FOO > works. Such code should not exist. > > In both cases, replacing tests of has_FOO by FOO reverts their sense. > We have to fix the value of FOO then. > > To facilitate review of the necessary updates to handwritten code, add > means to opt out of this change, and opt out for all QAPI schema > modules where the change requires updates to handwritten code. The > next few commits will remove these opt-outs in reviewable chunks, then > drop the means to opt out. > > Signed-off-by: Markus Armbruster > --- > docs/devel/qapi-code-gen.rst | 5 +-- > docs/devel/writing-monitor-commands.rst | 14 ++++---- > scripts/qapi/commands.py | 2 +- > scripts/qapi/events.py | 2 +- > scripts/qapi/gen.py | 2 +- > scripts/qapi/schema.py | 47 +++++++++++++++++++++++++ > scripts/qapi/types.py | 2 +- > scripts/qapi/visit.py | 17 +++++++-- > 8 files changed, 76 insertions(+), 15 deletions(-) > Reviewed-by: Daniel P. Berrangé With 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 :|