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 5EF80C433EF for ; Mon, 25 Oct 2021 04:34:09 +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 D652C60F4F for ; Mon, 25 Oct 2021 04:34:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org D652C60F4F 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]:50128 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mergW-000590-0b for qemu-devel@archiver.kernel.org; Mon, 25 Oct 2021 00:34:08 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:46582) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mereT-0002DC-TB for qemu-devel@nongnu.org; Mon, 25 Oct 2021 00:32:01 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:33929) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mereQ-0006Ew-SA for qemu-devel@nongnu.org; Mon, 25 Oct 2021 00:32:00 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1635136317; 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: in-reply-to:in-reply-to:references:references; bh=UYyuSREaFqnpSwCtq8fVzl/ie1dudV2d2dBxXa8dGqA=; b=JdWqTZXRxjUjk+JElbIguU1orZCDwr3T+LqVpICC2pUXSXzOkM/xxGhu3EEwskAKruLJUM YL2A7z3x9vVvFJuzkOyjXbjGKTX0Bym5tPPDesSIslUgjYEx8yun++EV6ejzkPd3lRDNAh mX5j5zmb9UZXcRJUQV6u1Z/fjHTDe0g= 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-108-ymNNH4TGP8GS-EtofLsdew-1; Mon, 25 Oct 2021 00:31:56 -0400 X-MC-Unique: ymNNH4TGP8GS-EtofLsdew-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 50F461006AA3; Mon, 25 Oct 2021 04:31:55 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-7.ams2.redhat.com [10.36.112.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0481B5DD68; Mon, 25 Oct 2021 04:31:38 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 8E68D11380A7; Mon, 25 Oct 2021 06:31:36 +0200 (CEST) From: Markus Armbruster To: qemu-devel@nongnu.org Subject: Re: [PATCH v3 1/5] qapi: Enable enum member introspection to show more than name References: <20211021102001.803780-1-armbru@redhat.com> <20211021102001.803780-2-armbru@redhat.com> Date: Mon, 25 Oct 2021 06:31:36 +0200 In-Reply-To: <20211021102001.803780-2-armbru@redhat.com> (Markus Armbruster's message of "Thu, 21 Oct 2021 12:19:57 +0200") Message-ID: <87h7d54tef.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@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: , Cc: kwolf@redhat.com, vsementsov@virtuozzo.com, berrange@redhat.com, libvir-list@redhat.com, eblake@redhat.com, mdroth@linux.vnet.ibm.com, pkrempa@redhat.com, marcandre.lureau@redhat.com, jsnow@redhat.com, libguestfs@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Markus Armbruster writes: > The next commit will add feature flags to enum members. There's a > problem, though: query-qmp-schema shows an enum type's members as an > array of member names (SchemaInfoEnum member @values). If it showed > an array of objects with a name member, we could simply add more > members to these objects. Since it's just strings, we can't. > > I can see three ways to correct this design mistake: > > 1. Do it the way we should have done it, plus compatibility goo. > > We want a ['SchemaInfoEnumMember'] member in SchemaInfoEnum. Since > changing @values would be a compatibility break, add a new member > @members instead. > > @values is now redundant. In my testing, output of > qemu-system-x86_64's query-qmp-schema grows by 11% (18.5KiB). > > We can deprecate @values now and drop it later. This will break > outmoded clients. Well-behaved clients such as libvirt are > expected to break cleanly. > > 2. Like 1, but omit "boring" elements of @member, and empty @member. > > @values does not become redundant. @members augments it. Somewhat > cumbersome, but output of query-qmp-schema grows only as we make > enum members non-boring. > > There is nothing to deprecate here. > > 3. Versioned query-qmp-schema. > > query-qmp-schema provides either @values or @members. The QMP > client can select which version it wants. There is no redundant > output. > > We can deprecate old versions and eventually drop them. This will > break outmoded clients. Breaking cleanly is easier than for 1. > > While 1 and 2 operate within the common rules for compatible > evolution apply (section "Compatibility considerations" in > docs/devel/qapi-code-gen.rst), 3 bypasses them. Attractive when > operating within the rules is just too awkward. Not the case here. > > This commit implements 1. Libvirt developers prefer it. > > Signed-off-by: Markus Armbruster > Reviewed-by: Eric Blake > Tested-by: Peter Krempa > Acked-by: Peter Krempa I meant to deprecate @values, but forgot. I should really do it right away, because... > --- > docs/devel/qapi-code-gen.rst | 15 +++++++++++---- > qapi/introspect.json | 21 +++++++++++++++++++-- > scripts/qapi/introspect.py | 18 ++++++++++++++---- > 3 files changed, 44 insertions(+), 10 deletions(-) > > diff --git a/docs/devel/qapi-code-gen.rst b/docs/devel/qapi-code-gen.rst > index b2569de486..d267889d2c 100644 > --- a/docs/devel/qapi-code-gen.rst > +++ b/docs/devel/qapi-code-gen.rst > @@ -1231,14 +1231,21 @@ Example: the SchemaInfo for ['str'] :: > "element-type": "str" } > > The SchemaInfo for an enumeration type has meta-type "enum" and > -variant member "values". The values are listed in no particular > -order; clients must search the entire enum when learning whether a > -particular value is supported. > +variant member "members". > + > +"members" is a JSON array describing the enumeration values. Each > +element is a JSON object with member "name" (the member's name). The > +"members" array is in no particular order; clients must search the > +entire array when learning whether a particular value is supported. > > Example: the SchemaInfo for MyEnum from section `Enumeration types`_ :: > > { "name": "MyEnum", "meta-type": "enum", > - "values": [ "value1", "value2", "value3" ] } > + "members": [ > + { "name": "value1" }, > + { "name": "value2" }, > + { "name": "value3" } > + ] } > > The SchemaInfo for a built-in type has the same name as the type in > the QAPI schema (see section `Built-in Types`_), with one exception ... this doesn't document @values anymore, only @members. Done in v5. [...]