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=-13.6 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 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 25451C433EF for ; Mon, 20 Sep 2021 07:48:23 +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 93A4B60F6E for ; Mon, 20 Sep 2021 07:48:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 93A4B60F6E 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]:48576 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mSE2H-0005vp-O9 for qemu-devel@archiver.kernel.org; Mon, 20 Sep 2021 03:48:21 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44634) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mSDyq-0000gQ-OE for qemu-devel@nongnu.org; Mon, 20 Sep 2021 03:44:48 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:44897) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mSDyn-0007yJ-SA for qemu-devel@nongnu.org; Mon, 20 Sep 2021 03:44:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1632123885; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Or9639w+kvOsVwXFchtwDibBSPMmqhe2Dh9xisQc+jQ=; b=Xhva3KiTIc2fzBS0OPMW4M5o+YC0sFHxu9fEJSf7YblUM5UA5MMx8hlAYjyPMrXJcJFWoG Q460hEMeG0nF+aWYsI5Li2OQng7+4fQUzFZbMfxgdKxKHtZbV7GywGszV+fUUhb0fmFs54 0gTJUTeuw4b+hJemGF8Qxf9xshhWeOA= 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-66-hJMhcfUCMuabuKvIGketiA-1; Mon, 20 Sep 2021 03:44:43 -0400 X-MC-Unique: hJMhcfUCMuabuKvIGketiA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6088E824FAF; Mon, 20 Sep 2021 07:44:40 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-14.ams2.redhat.com [10.36.112.14]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E1BC660C17; Mon, 20 Sep 2021 07:44:39 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 9B515113865F; Mon, 20 Sep 2021 09:44:38 +0200 (CEST) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Subject: Re: [PATCH v2 03/53] docs/devel: document expectations for QAPI data modelling for QMP References: <20210914142042.1655100-1-berrange@redhat.com> <20210914142042.1655100-4-berrange@redhat.com> Date: Mon, 20 Sep 2021 09:44:38 +0200 In-Reply-To: <20210914142042.1655100-4-berrange@redhat.com> ("Daniel P. =?utf-8?Q?Berrang=C3=A9=22's?= message of "Tue, 14 Sep 2021 15:19:52 +0100") Message-ID: <871r5j4ro9.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.476, 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: , Cc: Peter Maydell , Chris Wulff , David Hildenbrand , Bin Meng , Mark Cave-Ayland , qemu-devel@nongnu.org, Laurent Vivier , Max Filippov , Taylor Simpson , Alistair Francis , Gerd Hoffmann , "Edgar E. Iglesias" , Eric Blake , Marek Vasut , Yoshinori Sato , Markus Armbruster , Halil Pasic , Christian Borntraeger , Palmer Dabbelt , Artyom Tarasenko , Laurent Vivier , Thomas Huth , Eduardo Habkost , Richard Henderson , Greg Kurz , Yuval Shaia , qemu-s390x@nongnu.org, qemu-arm@nongnu.org, Michael Rolnik , Peter Xu , Stafford Horne , David Gibson , qemu-riscv@nongnu.org, Bastian Koppelmann , Cornelia Huck , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , qemu-ppc@nongnu.org, Aurelien Jarno , Paolo Bonzini , Aleksandar Rikalo , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Daniel P. Berrang=C3=A9 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. Berrang=C3=A9 > --- > docs/devel/writing-monitor-commands.rst | 27 +++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/docs/devel/writing-monitor-commands.rst b/docs/devel/writing= -monitor-commands.rst > index cddb36fb74..d68c552fdd 100644 > --- a/docs/devel/writing-monitor-commands.rst > +++ b/docs/devel/writing-monitor-commands.rst > @@ -350,6 +350,33 @@ In this section we will focus on user defined types.= Please, check the QAPI > documentation for information about the other types. > =20 > =20 > +Modelling data in QAPI > +~~~~~~~~~~~~~~~~~~~~~~ > + > +For a QMP command that to be considered stable and supported long term, > +there is a requirement returned data should be explicitly modelled > +using fine-grained 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, then 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 ad hoc 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 that contains formatted data, > +however, it is mandatory for the command to use the 'x-' name prefix. > +This indicates that the command is not guaranteed to be long term > +stable / liable to change in future and is not following QAPI design > +best practices. An example where this approach is taken is the QMP > +command "x-query-registers". This returns a formatted dump of the > +architecture specific CPU state. The way the data is formatted varies > +across QEMU targets, is liable to change over time, and is only > +intended to be consumed as an opaque string by machines. > + > User Defined Types > ~~~~~~~~~~~~~~~~~~ Reviewed-by: Markus Armbruster From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from list by lists.gnu.org with archive (Exim 4.90_1) id 1mSDyr-0000iA-A0 for mharc-qemu-riscv@gnu.org; Mon, 20 Sep 2021 03:44:49 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44620) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mSDyq-0000ef-1E for qemu-riscv@nongnu.org; Mon, 20 Sep 2021 03:44:48 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:43142) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mSDyn-0007yD-SH for qemu-riscv@nongnu.org; Mon, 20 Sep 2021 03:44:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1632123885; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Or9639w+kvOsVwXFchtwDibBSPMmqhe2Dh9xisQc+jQ=; b=Xhva3KiTIc2fzBS0OPMW4M5o+YC0sFHxu9fEJSf7YblUM5UA5MMx8hlAYjyPMrXJcJFWoG Q460hEMeG0nF+aWYsI5Li2OQng7+4fQUzFZbMfxgdKxKHtZbV7GywGszV+fUUhb0fmFs54 0gTJUTeuw4b+hJemGF8Qxf9xshhWeOA= 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-66-hJMhcfUCMuabuKvIGketiA-1; Mon, 20 Sep 2021 03:44:43 -0400 X-MC-Unique: hJMhcfUCMuabuKvIGketiA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6088E824FAF; Mon, 20 Sep 2021 07:44:40 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-14.ams2.redhat.com [10.36.112.14]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E1BC660C17; Mon, 20 Sep 2021 07:44:39 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 9B515113865F; Mon, 20 Sep 2021 09:44:38 +0200 (CEST) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Cc: qemu-devel@nongnu.org, Greg Kurz , Bin Meng , Yoshinori Sato , Stafford Horne , Cornelia Huck , David Hildenbrand , "Edgar E. Iglesias" , Jiaxun Yang , Peter Xu , Christian Borntraeger , qemu-ppc@nongnu.org, Mark Cave-Ayland , Paolo Bonzini , qemu-arm@nongnu.org, Michael Rolnik , Peter Maydell , Palmer Dabbelt , Alistair Francis , Halil Pasic , Taylor Simpson , Gerd Hoffmann , qemu-riscv@nongnu.org, Max Filippov , Yuval Shaia , Bastian Koppelmann , Artyom Tarasenko , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Thomas Huth , Aleksandar Rikalo , David Gibson , Marcel Apfelbaum , Laurent Vivier , "Dr. David Alan Gilbert" , Eduardo Habkost , Marek Vasut , Markus Armbruster , Aurelien Jarno , qemu-s390x@nongnu.org, Laurent Vivier , Eric Blake , Richard Henderson , Chris Wulff Subject: Re: [PATCH v2 03/53] docs/devel: document expectations for QAPI data modelling for QMP References: <20210914142042.1655100-1-berrange@redhat.com> <20210914142042.1655100-4-berrange@redhat.com> Date: Mon, 20 Sep 2021 09:44:38 +0200 In-Reply-To: <20210914142042.1655100-4-berrange@redhat.com> ("Daniel P. =?utf-8?Q?Berrang=C3=A9=22's?= message of "Tue, 14 Sep 2021 15:19:52 +0100") Message-ID: <871r5j4ro9.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.476, 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-riscv@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 20 Sep 2021 07:44:48 -0000 Daniel P. Berrang=C3=A9 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. Berrang=C3=A9 > --- > docs/devel/writing-monitor-commands.rst | 27 +++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/docs/devel/writing-monitor-commands.rst b/docs/devel/writing= -monitor-commands.rst > index cddb36fb74..d68c552fdd 100644 > --- a/docs/devel/writing-monitor-commands.rst > +++ b/docs/devel/writing-monitor-commands.rst > @@ -350,6 +350,33 @@ In this section we will focus on user defined types.= Please, check the QAPI > documentation for information about the other types. > =20 > =20 > +Modelling data in QAPI > +~~~~~~~~~~~~~~~~~~~~~~ > + > +For a QMP command that to be considered stable and supported long term, > +there is a requirement returned data should be explicitly modelled > +using fine-grained 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, then 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 ad hoc 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 that contains formatted data, > +however, it is mandatory for the command to use the 'x-' name prefix. > +This indicates that the command is not guaranteed to be long term > +stable / liable to change in future and is not following QAPI design > +best practices. An example where this approach is taken is the QMP > +command "x-query-registers". This returns a formatted dump of the > +architecture specific CPU state. The way the data is formatted varies > +across QEMU targets, is liable to change over time, and is only > +intended to be consumed as an opaque string by machines. > + > User Defined Types > ~~~~~~~~~~~~~~~~~~ Reviewed-by: Markus Armbruster