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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 81A1FC5B578 for ; Wed, 3 Jul 2019 05:07:13 +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 5732220989 for ; Wed, 3 Jul 2019 05:07:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5732220989 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]:60874 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hiXU7-0002zw-1c for qemu-devel@archiver.kernel.org; Wed, 03 Jul 2019 01:07:12 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:33547) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hiXTE-0002Vn-RC for qemu-devel@nongnu.org; Wed, 03 Jul 2019 01:06:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hiXT8-0004JO-6A for qemu-devel@nongnu.org; Wed, 03 Jul 2019 01:06:12 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51018) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hiXT7-00049Y-2M for qemu-devel@nongnu.org; Wed, 03 Jul 2019 01:06:10 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id B349781F0F; Wed, 3 Jul 2019 05:05:58 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-116-102.ams2.redhat.com [10.36.116.102]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8075B7E699; Wed, 3 Jul 2019 05:05:58 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id CAE1C1132ABF; Wed, 3 Jul 2019 07:05:56 +0200 (CEST) From: Markus Armbruster To: Paolo Bonzini Date: Wed, 03 Jul 2019 07:05:56 +0200 Message-ID: <878stfzozv.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Wed, 03 Jul 2019 05:05:58 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] What's IOMMUMemoryRegion's super? 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: Alexey Kardashevskiy , David Gibson , =?utf-8?Q?Daniel_P=2E_Berrang=C3=A9?= , qemu-devel@nongnu.org, Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" The usual QOM boilerplate for defining a sub-{type,class} looks like this: static const TypeInfo sysbus_device_type_info = { .name = TYPE_SYS_BUS_DEVICE, .parent = TYPE_DEVICE, .instance_size = sizeof(SysBusDevice), .abstract = true, .class_size = sizeof(SysBusDeviceClass), .class_init = sysbus_device_class_init, }; typedef struct SysBusDeviceClass { /*< private >*/ DeviceClass parent_class; [...] } SysBusDeviceClass; struct SysBusDevice { /*< private >*/ DeviceState parent_obj; [...] }; Note the TypeInfo states the parent type (member @parent), and associated class and instance structs (used members @instance_size and @class_size) have the parent type's class and member struct as first member. This makes type casts to parent types work. The checked QOM casts add safety by checking it's actually a parent type. Now consider TYPE_IOMMU_MEMORY_REGION: static const TypeInfo iommu_memory_region_info = { .parent = TYPE_MEMORY_REGION, .name = TYPE_IOMMU_MEMORY_REGION, .class_size = sizeof(IOMMUMemoryRegionClass), .instance_size = sizeof(IOMMUMemoryRegion), .instance_init = iommu_memory_region_initfn, .abstract = true, }; typedef struct IOMMUMemoryRegionClass { /* private */ ---> struct DeviceClass parent_class; [...] }; struct IOMMUMemoryRegion { MemoryRegion parent_obj; [...] }; The parent is TYPE_MEMORY_REGION, and the instance struct's first member is TYPE_MEMORY_REGION's instance struct as I expect, but the class struct's first member is something else entirely. What's going on here? Am I confused? The commit message is of no help whatsoever: commit 1221a4746769f70231beab4db8da1c937e60340c Author: Alexey Kardashevskiy Date: Tue Jul 11 13:56:20 2017 +1000 memory/iommu: introduce IOMMUMemoryRegionClass This finishes QOM'fication of IOMMUMemoryRegion by introducing a IOMMUMemoryRegionClass. This also provides a fastpath analog for IOMMU_MEMORY_REGION_GET_CLASS(). This makes IOMMUMemoryRegion an abstract class. Signed-off-by: Alexey Kardashevskiy Message-Id: <20170711035620.4232-3-aik@ozlabs.ru> Acked-by: Cornelia Huck Signed-off-by: Paolo Bonzini