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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id BA4DAC61DA4 for ; Thu, 9 Feb 2023 10:44:23 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pQ4PP-0006Id-RY; Thu, 09 Feb 2023 05:44:07 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pQ4PN-0006IJ-PC for qemu-devel@nongnu.org; Thu, 09 Feb 2023 05:44:05 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pQ4PM-0002dQ-1q for qemu-devel@nongnu.org; Thu, 09 Feb 2023 05:44:05 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1675939443; 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=v8xtL8UusMdyMqz6MEKt3ZGo8c9Yr6QbuhQyBN+hTec=; b=Dop6HjG90h9GM/+ZMNYl02i9DleSs7QBU+fAutlQW4PESy1mxP+YDLDEIg5MaKIryDzGyO lbxbmuKOxRK75u9KdBXmuHonA9HVV35pbdux9ujLPWmaAo6TuV9mWCH9Ff6Vt9dKeR9YJm lakf7UCEFw6CNwVoSfOPPKZDoAU/WH0= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-351-VbrW6QIXMkWcruGgX6MOmA-1; Thu, 09 Feb 2023 05:43:58 -0500 X-MC-Unique: VbrW6QIXMkWcruGgX6MOmA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 57244802314; Thu, 9 Feb 2023 10:43:57 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.193.101]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D8DF740C83B6; Thu, 9 Feb 2023 10:43:56 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id A94E021E6A1F; Thu, 9 Feb 2023 11:43:55 +0100 (CET) From: Markus Armbruster To: Peter Maydell Cc: qemu-devel@nongnu.org, Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Thomas Huth , Paolo Bonzini , "Daniel P. Berrange" , Eduardo Habkost , =?utf-8?Q?C=C3=A9dric?= Le Goater , Mark Cave-Ayland , Mark Burton , Luc Michel , Bernhard Beschow , Bin Meng , Alistair Francis Subject: Re: Can we unpoison CONFIG_FOO macros? References: <87lel9o56z.fsf@pond.sub.org> Date: Thu, 09 Feb 2023 11:43:55 +0100 In-Reply-To: (Peter Maydell's message of "Tue, 7 Feb 2023 15:50:41 +0000") Message-ID: <874jrv6rv8.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_NONE=-0.0001, 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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Peter Maydell writes: > On Tue, 7 Feb 2023 at 15:41, Markus Armbruster wrote: >> We have a boatload of CONFIG_FOO macros that may only be used in >> target-dependent code. We use generated config-poison.h to enforce. >> >> This is a bit annoying in the QAPI schema. Let me demonstrate with an >> example: QMP commands query-rocker, query-rocker-ports, and so forth. >> These commands are useful only with "rocker" devices. They are >> compile-time optional. hw/net/Kconfig: >> >> config ROCKER >> bool >> default y if PCI_DEVICES >> depends on PCI && MSI_NONBROKEN >> >> The rocker device and QMP code is actually target-independent: >> hw/net/meson.build puts it into softmmu_ss. >> >> Disabling the "rocker" device type ideally disables the rocker QMP >> commands, too. Should be easy enough: 'if': 'CONFIG_FOO' in the QAPI >> schema. >> >> Except that makes the entire code QAPI generates for rocker.json >> device-dependent: it now contains #if defined(CONFIG_ROCKER), and >> CONFIG_ROCKER is poisoned. The rocker code implementing monitor >> commands also becomes device-dependent, because it includes generated >> headers. We compile all that per target for no sane reason at all. >> That's why we don't actually disable the commands. >> >> Not disabling them creates another problem: we have the commands always, >> but their implementation depends on CONFIG_ROCKER. So we provide stubs >> that always fail for use when CONFIG_ROCKER is off. Drawbacks: we >> generate, compile and link useless code, and QAPI/QMP introspection is >> less useful than it could be. > > If you want the introspection to be useful, then you need to > make the appearance of the commands depend on what machine > type and devices are created on the command line. There are > lots of machine types where the rocker commands are irrelevant > because they don't apply to that machine even though it happens > that PCI_DEVICES got built into that QEMU executable. > > I think the underlying question is "what does it mean to be > only building in a QMP command when a Kconfig value is set?". > It doesn't mean "this command only appears when it's useful", > so anybody introspecting with QMP has to handle the "command > exists but doesn't do anything helpful" case anyway. My guess > is that the check you're trying to do at compile time ought > to be done at runtime somehow instead (which is a general > theme for 'single system emulation executable' work). For better or worse, QAPI/QMP introspection is compile-time static. It's oblivious of run-time configuration and state. You point out that the question "is rocker built into this binary" isn't particularly interesting. You're right. Still, it's a kind of question static introspection *should* be able to answer. Due to the way our compile time configuration machinery works, QAPI/QMP introspection can't actually answer it, and that irks me. For the same reason, we can't fully disable things like rocker: the generated QAPI code remains along with command stubs. Irks me, too. Neither is a serious problem for us as far as I can tell. As I wrote: > This isn't terrible. It still annoys me. I wonder whether Philippe's > work on having a single qemu-system binary could improve things here.