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=-6.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 39CBFC433E0 for ; Fri, 31 Jul 2020 13:47:39 +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 058A6208E4 for ; Fri, 31 Jul 2020 13:47:39 +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="Y19BiLWu" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 058A6208E4 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]:50696 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1k1VNq-0004lL-9M for qemu-devel@archiver.kernel.org; Fri, 31 Jul 2020 09:47:38 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44040) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k1VNB-0004D5-BG for qemu-devel@nongnu.org; Fri, 31 Jul 2020 09:46:57 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:47511 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 1k1VN8-0002Es-7f for qemu-devel@nongnu.org; Fri, 31 Jul 2020 09:46:57 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596203212; 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=FKGR5FsMX/sDWugDb5Atfb1RE5Cjh67rKMOizGy++SM=; b=Y19BiLWuSjMhJoczXz5GMyYF/s0+kcEm8IyCUQ0ANDSkaWUOKy0wR7AqVFrpDMTNcOjaWG yus+/XLL0KrNunIqMDoJCyMRRDTGC4tTY4gYW/CdqxOwVe6Krsrq7pNnnK4+jElOI8poeC JvtBt9akTxAYkH0BK3xFIC9trnhKMRw= 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-221-tAIlcM1RPQe2E2q5tU0PEQ-1; Fri, 31 Jul 2020 09:46:48 -0400 X-MC-Unique: tAIlcM1RPQe2E2q5tU0PEQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4CD4B800470; Fri, 31 Jul 2020 13:46:47 +0000 (UTC) Received: from [10.3.113.226] (ovpn-113-226.phx2.redhat.com [10.3.113.226]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DA8A074F4A; Fri, 31 Jul 2020 13:46:46 +0000 (UTC) Subject: Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id() To: Markus Armbruster 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> <87pn8ct9ga.fsf@dusky.pond.sub.org> From: Eric Blake Organization: Red Hat, Inc. Message-ID: <53b70f7f-1777-64e5-d80f-6af3d6c1252d@redhat.com> Date: Fri, 31 Jul 2020 08:46:40 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <87pn8ct9ga.fsf@dusky.pond.sub.org> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.81; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/31 08:55:49 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-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 , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/31/20 2:44 AM, Markus Armbruster wrote: >>> 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? I'm in favor of 2, but can easily live with 1 if we decide to be that much more conservative. Tooling that can't handle a missing value is not going to fare any better with a value that is unusable because it is -1, but the important point is that I don't think we have a scenario with such tooling depending on the value (the tools that DO depend on the value are built on platforms where the value is usable). -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org