From nobody Tue Feb 10 05:50:30 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1528750480236134.4087278965893; Mon, 11 Jun 2018 13:54:40 -0700 (PDT) Received: from localhost ([::1]:51295 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fSTpj-000378-KQ for importer@patchew.org; Mon, 11 Jun 2018 16:54:35 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43625) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fSTnX-0001jc-2Z for qemu-devel@nongnu.org; Mon, 11 Jun 2018 16:52:20 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fSTnV-00082M-O9 for qemu-devel@nongnu.org; Mon, 11 Jun 2018 16:52:19 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:49080 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fSTnQ-0007xO-R5; Mon, 11 Jun 2018 16:52:12 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 58958401EF1C; Mon, 11 Jun 2018 20:52:12 +0000 (UTC) Received: from localhost (ovpn-204-89.brq.redhat.com [10.40.204.89]) by smtp.corp.redhat.com (Postfix) with ESMTPS id ECBEE2035721; Mon, 11 Jun 2018 20:52:11 +0000 (UTC) From: Max Reitz To: qemu-block@nongnu.org Date: Mon, 11 Jun 2018 22:51:55 +0200 Message-Id: <20180611205203.2624-3-mreitz@redhat.com> In-Reply-To: <20180611205203.2624-1-mreitz@redhat.com> References: <20180611205203.2624-1-mreitz@redhat.com> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Mon, 11 Jun 2018 20:52:12 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Mon, 11 Jun 2018 20:52:12 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'mreitz@redhat.com' RCPT:'' X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 66.187.233.73 Subject: [Qemu-devel] [PATCH v2 02/10] docs/qapi: Document optional discriminators X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , qemu-devel@nongnu.org, Michael Roth , Markus Armbruster , Max Reitz Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Reviewed-by: Eric Blake Signed-off-by: Max Reitz --- docs/devel/qapi-code-gen.txt | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/docs/devel/qapi-code-gen.txt b/docs/devel/qapi-code-gen.txt index 1366228b2a..f0a2101096 100644 --- a/docs/devel/qapi-code-gen.txt +++ b/docs/devel/qapi-code-gen.txt @@ -472,8 +472,8 @@ All branches of the union must be complex types, and th= e top-level members of the union dictionary on the wire will be combination of members from both the base type and the appropriate branch type (when merging two dictionaries, there must be no keys in common). The -'discriminator' member must be the name of a non-optional enum-typed -member of the base struct. +'discriminator' member must be the name of an enum-typed member of the +base struct. =20 The following example enhances the above simple union example by adding an optional common member 'read-only', renaming the @@ -502,6 +502,23 @@ the enum). In the resulting generated C data types, a= flat union is represented as a struct with the base members included directly, and then a union of structures for each branch of the struct. =20 +If the discriminator points to an optional member of the base struct, +its default value must be specified as a 'default-variant'. In the +following example, the above BlockDriver struct is changed so it +defaults to the 'file' driver if that field is omitted on the wire: + + { 'union': 'BlockdevOptions', + 'base': { '*driver': 'BlockdevDriver', '*read-only': 'bool' }, + 'discriminator': 'driver', + 'default-variant': 'file', + 'data': { 'file': 'BlockdevOptionsFile', + 'qcow2': 'BlockdevOptionsQcow2' } } + +Now the 'file' JSON object can be abbreviated to: + + { "read-only": "true", + "filename": "/some/place/my-image" } + A simple union can always be re-written as a flat union where the base class has a single member named 'type', and where each branch of the union has a struct with a single member named 'data'. That is, --=20 2.17.1