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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 02D97C433E1 for ; Thu, 16 Jul 2020 22:22:24 +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 B92AB207DD for ; Thu, 16 Jul 2020 22:22:24 +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="dX9Yr7wZ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B92AB207DD 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]:38330 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jwCGm-0002tM-1v for qemu-devel@archiver.kernel.org; Thu, 16 Jul 2020 18:22:24 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59502) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jwCG4-0002QB-Bo for qemu-devel@nongnu.org; Thu, 16 Jul 2020 18:21:40 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:37744 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jwCG1-0007mK-PL for qemu-devel@nongnu.org; Thu, 16 Jul 2020 18:21:39 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1594938096; 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=+q7/sEJ73N6zfPZJBh83bZ1wXwyZ+AGf4cECSGLmj4s=; b=dX9Yr7wZKcNB2htFwvCFO5OHks+avWy6XjXx2j8KIsM0+hIKhi7le6NqkoC/e9VOeRajZ8 dTA5kaXQOlr8FXo7y2CH/TTvmoaw0uaEFZTVkdNfnWfJKea1ZVa0fpK9fDZjBrKedJP0n2 AsdDLijvOWti3zHI1ITB4Zn+W4mEDK8= 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-296-dKrHDvqUNzerexU-E5ZBzA-1; Thu, 16 Jul 2020 18:21:33 -0400 X-MC-Unique: dKrHDvqUNzerexU-E5ZBzA-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 0F4701085; Thu, 16 Jul 2020 22:21:32 +0000 (UTC) Received: from localhost (ovpn-119-232.rdu2.redhat.com [10.10.119.232]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9B2575D9E4; Thu, 16 Jul 2020 22:21:31 +0000 (UTC) Date: Thu, 16 Jul 2020 18:21:30 -0400 From: Eduardo Habkost To: Markus Armbruster Subject: Re: sysbus_create_simple Vs qdev_create Message-ID: <20200716222130.GO1274972@habkost.net> References: <87365t18mp.fsf@dusky.pond.sub.org> <87lfjkvo81.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87lfjkvo81.fsf@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.61; envelope-from=ehabkost@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/16 18:21:36 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, 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: Paolo Bonzini , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , qemu-devel@nongnu.org, Pratik Parvati Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 15, 2020 at 04:37:18PM +0200, Markus Armbruster wrote: > Pratik Parvati writes: > > > Hi Markus and Philippe, > > > > Thanks for your reply. Now I am pretty clear about Qdev and sysbus helper > > function. > > > > Can you please explain to me in brief on buses and device hierarchies (i.e. > > BusState and DeviceState) and how they are related to each other? As I can > > see, the DeviceState class inherits the BusState > > > > struct DeviceState { > > /*< private >*/ > > Object parent_obj; > > /*< public >*/ > > > > const char *id; > > char *canonical_path; > > bool realized; > > bool pending_deleted_event; > > QemuOpts *opts; > > int hotplugged; > > bool allow_unplug_during_migration; > > BusState *parent_bus; \\ BusState is inherited here > > QLIST_HEAD(, NamedGPIOList) gpios; > > QLIST_HEAD(, BusState) child_bus; > > int num_child_bus; > > int instance_id_alias; > > int alias_required_for_version; > > ResettableState reset; > > }; > > > > and BusState, in turn, inherits the DeviceState as > > > > /** > > * BusState: > > * @hotplug_handler: link to a hotplug handler associated with bus. > > * @reset: ResettableState for the bus; handled by Resettable interface. > > */struct BusState { > > Object obj; > > DeviceState *parent; \\ DeviceState is inherited here > > char *name; > > HotplugHandler *hotplug_handler; > > int max_index; > > bool realized; > > int num_children; > > QTAILQ_HEAD(, BusChild) children; > > QLIST_ENTRY(BusState) sibling; > > ResettableState reset; > > }; > > > > I am a bit confused. Can you brief me this relation! > > We sorely lack introductory documentation on both qdev and QOM. I > believe most developers are more or less confused about them most of the > time. I've done a bit of work on both, so I'm probably less confused > than average. I'm cc'ing maintainers in the hope of reducing average > confusion among participants in this thread. > > DeviceState does not inherit from BusState, and BusState does not > inherit from DeviceState. The relation you marked in the code is > actually "has a". > > A DeviceState may have a BusState, namely the bus the device is plugged > into. "May", because some devices are bus-less (their > DEVICE_GET_CLASS(dev)->bus_type is null), and the others get plugged > into their bus only at realize time. > > Example: PCI device "pci-serial" plugs into a PCI bus. > > Example: device "serial" does not plug into a bus (its used as component > device of "pci-serial" and other devices). > > Example: device "pc-dimm" does not plug into a bus. > > A bus has a DeviceState, namely the device providing this bus. > > Example: device "i440FX-pcihost" provides PCI bus "pci.0". > > Both DeviceState and BusState are QOM subtypes of Object. I prefer to > avoid use of "inherit" for that, because it can mean different things to > different people. I'd also note that the use of "parent" in the code is also ambiguous. It can mean: * QOM parent type, i.e. TypeInfo.parent. Related fields: * parent_class members of class structs * parent_obj members of object structs * QOM composition tree parent object, i.e. Object::parent * qdev device parent bus, i.e. DeviceState::parent_bus * parent device of of qdev bus, i.e. BusState::parent -- Eduardo