From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from list by lists.gnu.org with archive (Exim 4.90_1) id 1k1Pih-0008M2-UH for mharc-qemu-trivial@gnu.org; Fri, 31 Jul 2020 03:44:47 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:50670) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k1Pih-0008Ln-3O for qemu-trivial@nongnu.org; Fri, 31 Jul 2020 03:44:47 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:37547 helo=us-smtp-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 1k1Pie-0008IP-AG for qemu-trivial@nongnu.org; Fri, 31 Jul 2020 03:44:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596181482; 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=1UdoygK3os5o72+8NFLQ+SCSJV9B0RM5JrZKIjlH2/c=; b=IH/XTwIfuENgtdXpFdRFDVwA3+nNy7Yjb7+5mkoWRY4ruR88sjC3fIGU7x4lYreMU48zI4 g8D+wjJI6lAtcoSXIko6ACk6SHZV4Uv/HDV5ao67RFQLlgrRgc9nx/zkuoHXFcrHO6hROZ hxTHOTxddQ1oQkwj+zoK2u0NfiO+xJE= 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-500-i5U6w9nNMwagjtd9X6eCfw-1; Fri, 31 Jul 2020 03:44:40 -0400 X-MC-Unique: i5U6w9nNMwagjtd9X6eCfw-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 54F30100CCC5; Fri, 31 Jul 2020 07:44:39 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-143.ams2.redhat.com [10.36.112.143]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E85D35DA75; Fri, 31 Jul 2020 07:44:38 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 678151132FD2; Fri, 31 Jul 2020 09:44:37 +0200 (CEST) From: Markus Armbruster To: Eric Blake Cc: Daniel P. =?utf-8?Q?Berrang=C3=A9?= , Peter Maydell , QEMU Trivial , QEMU Developers Subject: Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id() References: <20200716154114.10838-1-peter.maydell@linaro.org> <0f8b8fea-2bd0-7616-292b-8fb0f87cec75@redhat.com> <87k0ylvy0t.fsf@dusky.pond.sub.org> <20200730155939.GP3477223@redhat.com> <4d2cba04-04d8-9b82-562f-acb84b6010d2@redhat.com> Date: Fri, 31 Jul 2020 09:44:37 +0200 In-Reply-To: <4d2cba04-04d8-9b82-562f-acb84b6010d2@redhat.com> (Eric Blake's message of "Thu, 30 Jul 2020 11:24:51 -0500") Message-ID: <87pn8ct9ga.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 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=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=205.139.110.120; envelope-from=armbru@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/31 03:06:50 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=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-trivial@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: Fri, 31 Jul 2020 07:44:47 -0000 Eric Blake writes: > On 7/30/20 10:59 AM, Daniel P. Berrang=C3=A9 wrote: > >>> Well, I suspect that management-layer code currently has >>> gone for "assume we're always running on Linux" and was >>> written by people who knew they were getting a Linux tid... >> >> Yes, on the libvirt side, the functionality that relies on thread_is is >> only compiled on Linux. If someone wants to use it on other OS, they'll >> have to provide an impl using their platforms equivalent of >> sched_setaffinity and friends since none of this stuff is standardized >> across OS. >> >> >>>> The PID is quite unlikely to be "an OS-specific identifier of the >>>> current thread". Shouldn't we fail instead of lie when we don't know >>>> how to compute the truth? >>> >>> Yeah, I think the default codepath is pretty bogus too. Should >>> the QMP functions have a mechanism for saying "we don't know >>> a thread-id on this platform" ? >> >> Thread_id should be optional and thus not filled in if we >> can't provide a sensible value. Unfortunately we made it >> mandatory in QMP. > > Normally, converting a mandatory output value to optional is a > back-compatibility risk (we could break apps that depended on it being > present). But if the only apps that depended on it being present are > compiled on Linux, where the member will actually be present, I think > that changing the schema to make it optional for non-Linux platforms > won't be a back-compatibility nightmare (but we will have to be > careful in our documentation). Options for systems where don't know how to compute a system-wide thread ID: 0. Return a bogus value: the PID. This is the status quo. 1. Return a more obviously bogus value: -1. Semantic compatibility break. Should be harmless, because a QMP client relying on the thread-id being the PID would be insane. 2. Make thread-id optional, present iff we can compute a value. This is what we should have done, but we didn't, and now it's a syntactic compatibility break. Matters only if it actually breaks QMP clients. We believe the one we know shouldn't break. Preferences? 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 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 91AE8C433DF for ; Fri, 31 Jul 2020 07:45:36 +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 5A2782067D for ; Fri, 31 Jul 2020 07:45:36 +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="IH/XTwIf" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5A2782067D 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]:39182 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1k1PjT-0000Yt-Hm for qemu-devel@archiver.kernel.org; Fri, 31 Jul 2020 03:45:35 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:50668) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k1Pih-0008Lj-27 for qemu-devel@nongnu.org; Fri, 31 Jul 2020 03:44:47 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:45175 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 1k1Pie-0008IO-7E for qemu-devel@nongnu.org; Fri, 31 Jul 2020 03:44:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596181482; 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Fri, 31 Jul 2020 07:44:38 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 678151132FD2; Fri, 31 Jul 2020 09:44:37 +0200 (CEST) From: Markus Armbruster To: Eric Blake Subject: Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id() References: <20200716154114.10838-1-peter.maydell@linaro.org> <0f8b8fea-2bd0-7616-292b-8fb0f87cec75@redhat.com> <87k0ylvy0t.fsf@dusky.pond.sub.org> <20200730155939.GP3477223@redhat.com> <4d2cba04-04d8-9b82-562f-acb84b6010d2@redhat.com> Date: Fri, 31 Jul 2020 09:44:37 +0200 In-Reply-To: <4d2cba04-04d8-9b82-562f-acb84b6010d2@redhat.com> (Eric Blake's message of "Thu, 30 Jul 2020 11:24:51 -0500") Message-ID: <87pn8ct9ga.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 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=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=205.139.110.61; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/31 02:46:11 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: QEMU Trivial , Peter Maydell , "Daniel P. =?utf-8?Q?Berrang=C3=A9?=" , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Eric Blake writes: > On 7/30/20 10:59 AM, Daniel P. Berrang=C3=A9 wrote: > >>> Well, I suspect that management-layer code currently has >>> gone for "assume we're always running on Linux" and was >>> written by people who knew they were getting a Linux tid... >> >> Yes, on the libvirt side, the functionality that relies on thread_is is >> only compiled on Linux. If someone wants to use it on other OS, they'll >> have to provide an impl using their platforms equivalent of >> sched_setaffinity and friends since none of this stuff is standardized >> across OS. >> >> >>>> The PID is quite unlikely to be "an OS-specific identifier of the >>>> current thread". Shouldn't we fail instead of lie when we don't know >>>> how to compute the truth? >>> >>> Yeah, I think the default codepath is pretty bogus too. Should >>> the QMP functions have a mechanism for saying "we don't know >>> a thread-id on this platform" ? >> >> Thread_id should be optional and thus not filled in if we >> can't provide a sensible value. Unfortunately we made it >> mandatory in QMP. > > Normally, converting a mandatory output value to optional is a > back-compatibility risk (we could break apps that depended on it being > present). But if the only apps that depended on it being present are > compiled on Linux, where the member will actually be present, I think > that changing the schema to make it optional for non-Linux platforms > won't be a back-compatibility nightmare (but we will have to be > careful in our documentation). Options for systems where don't know how to compute a system-wide thread ID: 0. Return a bogus value: the PID. This is the status quo. 1. Return a more obviously bogus value: -1. Semantic compatibility break. Should be harmless, because a QMP client relying on the thread-id being the PID would be insane. 2. Make thread-id optional, present iff we can compute a value. This is what we should have done, but we didn't, and now it's a syntactic compatibility break. Matters only if it actually breaks QMP clients. We believe the one we know shouldn't break. Preferences?