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=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 DF013C433F5 for ; Fri, 10 Sep 2021 12:54:55 +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 546F561167 for ; Fri, 10 Sep 2021 12:54:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 546F561167 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]:58270 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mOg3S-0006rE-CO for qemu-devel@archiver.kernel.org; Fri, 10 Sep 2021 08:54:54 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:38152) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mOfvy-0006e5-PT for qemu-devel@nongnu.org; Fri, 10 Sep 2021 08:47:12 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:27474) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mOfvw-00070b-6z for qemu-devel@nongnu.org; Fri, 10 Sep 2021 08:47:10 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631278027; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+yvsMBm+onPevTFHQMyBNn2F1gMnjnBfGqPcoeUVyzY=; b=UsEnTLQVwP6xKhWBfoI2zpqJ4uysaui/4+PVqj1MAngLPup5chGC3vJW12YttdoDbp3ein XNRkHT7mI6MTZdjzC6LgCICg6HbBFDOvaR7fmvZpgeJQ5kMm/pBxOcLBEUyPJeYwpW9PF9 tTKslvg/gkg7AupUV3ruQ+iWfAOJcwo= 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-34-qiEApkVPPZ2aMgZUc-Aj1g-1; Fri, 10 Sep 2021 08:47:03 -0400 X-MC-Unique: qiEApkVPPZ2aMgZUc-Aj1g-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F3CA5835DEE; Fri, 10 Sep 2021 12:47:02 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.181]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9C53A5C1A1; Fri, 10 Sep 2021 12:47:01 +0000 (UTC) Date: Fri, 10 Sep 2021 13:46:59 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Subject: Re: [PATCH 1/5] docs/devel: document expectations for QAPI data modelling for QMP Message-ID: References: <20210908103711.683940-1-berrange@redhat.com> <20210908103711.683940-2-berrange@redhat.com> <87tuium6u7.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87tuium6u7.fsf@dusky.pond.sub.org> User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.392, 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Eduardo Habkost , Eric Blake , qemu-devel@nongnu.org, "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Sep 09, 2021 at 11:33:20AM +0200, Markus Armbruster wrote: > Daniel P. Berrangé writes: > > > Traditionally we have required that newly added QMP commands will model > > any returned data using fine grained QAPI types. This is good for > > commands that are intended to be consumed by machines, where clear data > > representation is very important. Commands that don't satisfy this have > > generally been added to HMP only. > > > > In effect the decision of whether to add a new command to QMP vs HMP has > > been used as a proxy for the decision of whether the cost of designing a > > fine grained QAPI type is justified by the potential benefits. > > > > As a result the commands present in QMP and HMP are non-overlapping > > sets, although HMP comamnds can be accessed indirectly via the QMP > > command 'human-monitor-command'. > > > > One of the downsides of 'human-monitor-command' is that the QEMU monitor > > APIs remain tied into various internal parts of the QEMU code. For > > example any exclusively HMP command will need to use 'monitor_printf' > > to get data out. It would be desirable to be able to fully isolate the > > monitor implementation from QEMU internals, however, this is only > > possible if all commands are exclusively based on QAPI with direct > > QMP exposure. > > > > The way to achieve this desired end goal is to finese the requirements > > for QMP command design. For cases where the output of a command is only > > intended for human consumption, it is reasonable to want to simplify > > the implementation by returning a plain string containing formatted > > data instead of designing a fine grained QAPI data type. This can be > > permitted if-and-only-if the command is exposed under the 'x-' name > > prefix. This indicates that the command data format is liable to > > future change and that it is not following QAPI design best practice. > > > > The poster child example for this would be the 'info registers' HMP > > command which returns printf formatted data representing CPU state. > > This information varies enourmously across target architectures and > > changes relatively frequently as new CPU features are implemented. > > It is there as debugging data for human operators, and any machine > > usage would treat it as an opaque blob. It is thus reasonable to > > expose this in QMP as 'x-query-registers' returning a 'str' field. > > > > Signed-off-by: Daniel P. Berrangé > > --- > > docs/devel/writing-qmp-commands.rst | 25 +++++++++++++++++++++++++ > > 1 file changed, 25 insertions(+) > > +QAPI types. As a general guide, a caller of the QMP command should never need > > +to parse individual returned data fields. If a field appears to need parsing, > > +them it should be split into separate fields corresponding to each distinct > > +data item. This should be the common case for any new QMP command that is > > +intended to be used by machines, as opposed to exclusively human operators. > > + > > +Some QMP commands, however, are only intended as adhoc debugging aids for human > > +operators. While they may return large amounts of formatted data, it is not > > +expected that machines will need to parse the result. The overhead of defining > > +a fine grained QAPI type for the data may not be justified by the potential > > +benefit. In such cases, it is permitted to have a command return a simple string > > There are many existing long lines in this file, so I'm not flagging > yours, except for this one, because it increases the maximum. This line is at exactly 80 characters so checkstyle is happy with it. We don't have any requirement for a differenet line limit for docs afair ? Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|