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=-3.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS autolearn=no 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 21FCEC432C0 for ; Thu, 21 Nov 2019 15:08:58 +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 E096B20674 for ; Thu, 21 Nov 2019 15:08:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="LmCfrCPM" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E096B20674 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:41690 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iXo4n-0002St-1Y for qemu-devel@archiver.kernel.org; Thu, 21 Nov 2019 10:08:57 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:47058) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iXo3k-0001Yy-QD for qemu-devel@nongnu.org; Thu, 21 Nov 2019 10:07:53 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iXo3i-0007QD-Pe for qemu-devel@nongnu.org; Thu, 21 Nov 2019 10:07:51 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:50083 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iXo3i-0007PM-Lz for qemu-devel@nongnu.org; Thu, 21 Nov 2019 10:07:50 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1574348869; h=from:from: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=DjIMR8kAUCZNQt0MnGI8WLQ5h5+Z52ER0l1AL7AjP9E=; b=LmCfrCPMkJGA4FGWXuIUrerfdzw44pF4OAjZxVm4/5QMJsHoYEmxVZklMaaw7+36YwGWqx 5FRM197QLmqCOErLKUI4Yyd6EGLYOnUXYw8PYVuYFOoydd0C2aG3ntFv45ngIhZyNenNVi 6+5vhdazYfY40Z9Ao5KAbKIZ+XcnNnE= 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-141-qGzsot_0NqqzYixgyDLuBw-1; Thu, 21 Nov 2019 10:07:48 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 23483DB76; Thu, 21 Nov 2019 15:07:47 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-116-134.ams2.redhat.com [10.36.116.134]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E320F537B8; Thu, 21 Nov 2019 15:07:46 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 63D051138606; Thu, 21 Nov 2019 16:07:45 +0100 (CET) From: Markus Armbruster To: Max Reitz Subject: Re: [Qemu-devel] [PATCH v4 03/14] qapi: Introduce default values for struct members References: <20190624173935.25747-1-mreitz@redhat.com> <20190624173935.25747-4-mreitz@redhat.com> Date: Thu, 21 Nov 2019 16:07:45 +0100 In-Reply-To: <20190624173935.25747-4-mreitz@redhat.com> (Max Reitz's message of "Mon, 24 Jun 2019 19:39:23 +0200") Message-ID: <87eey1b73y.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-MC-Unique: qGzsot_0NqqzYixgyDLuBw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 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: , Cc: Kevin Wolf , qemu-devel@nongnu.org, qemu-block@nongnu.org, Michael Roth Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Max Reitz writes: > With this change, it is possible to give default values for struct > members, as follows: > > What you had to do so far: > > # @member: Some description, defaults to 42. > { 'struct': 'Foo', > 'data': { '*member': 'int' } } > > What you can do now: > > { 'struct': 'Foo', > 'data': { '*member': { 'type': 'int', 'default': 42 } } The '*' is redundant in this form. Can anyone think of reasons for keeping it anyway? Against? > On the C side, this change would remove Foo.has_member, because > Foo.member is always valid now. The input visitor deals with setting > it. (Naturally, this means that such defaults are useful only for input > parameters.) > > At least three things are left unimplemented: > > First, support for alternate data types. This is because supporting > them would mean having to allocate the object in the input visitor, and > then potentially going through multiple levels of nested types. In any > case, it would have been difficult and I do not think there is need for > such support at this point. > > Second, support for null. The most important reason for this is that > introspection already uses "'default': null" for "no default, but this > field is optional". The second reason is that without support for > alternate data types, there is not really a point in supporting null. > > Third, full support for default lists. This has a similar reason to the > lack of support for alternate data types: Allocating a default list is > not trivial -- unless the list is empty, which is exactly what we have > support for. > > Signed-off-by: Max Reitz