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=-9.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 9F81DC433DF for ; Thu, 30 Jul 2020 16:07:01 +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 6A29A20829 for ; Thu, 30 Jul 2020 16:07:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="y6W8Lvr2" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6A29A20829 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linaro.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:35440 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1k1B5A-0005wc-Mr for qemu-devel@archiver.kernel.org; Thu, 30 Jul 2020 12:07:00 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:57492) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k1Ari-00038f-OM for qemu-devel@nongnu.org; Thu, 30 Jul 2020 11:53:07 -0400 Received: from mail-oi1-x242.google.com ([2607:f8b0:4864:20::242]:40891) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1k1Are-0004cg-UX for qemu-devel@nongnu.org; Thu, 30 Jul 2020 11:53:06 -0400 Received: by mail-oi1-x242.google.com with SMTP id u24so14246463oiv.7 for ; Thu, 30 Jul 2020 08:53:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=+IMqDkH3Yx+rnYKl9GUMAPJpANuQ/vc8DzNV0oiunpA=; b=y6W8Lvr2JetNvz5HQsgEpqon74FE+Uj97qKt+bvRl5x105BUqxy+f+B8WHtx9Xvgp9 5PKZY80sESt7oAIwPoHQR+x4H8hln6IS47jQiDgDK6e7ZBs599I9ccs+HwF++8VORxrg KXIIJ73IA427ICJGY0BEoQcZQAqmgSDlp4nA0Mich3dhz1EFeqlP6GWJYho2NP0xyghQ /ErJHApPFRUtP/HQ88e9ELqopTEA1Pn4+hKqK2VPXs0ttUMfhJGgGzEenGHRHU1N5KhC MPpeh0p1p+u3sRUzdy0/ax+830KLb5Vcv4J+p75wrcSbi6PNKR8I6k4f/Ckf3x6QIXCK nr2Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=+IMqDkH3Yx+rnYKl9GUMAPJpANuQ/vc8DzNV0oiunpA=; b=LLCAucc2mLHej3FWpPtXGLEzgMMkjFABcthZp21eHVc5rplx+rZ/JgYHloo1EqgUkd z16CNEm14eeJf1G27PHgRY+37IOlzMcJehNwBr5P5oTDqGKrMMaid6fsOWDA351Q0F4Z YAofu9DBptRJCRAJycjQHDW4kEtYmXo83pbqdrbxZcXm/wJq9UijOGQIzUowRxGAZCTv 6jO4Ug153EkWwOO/7vuRz2pwQhs4EkqEi2M90WhN9UEeiyRkv7nG8NB6WDREdPCz6Bs5 R0tDORwEbFHiPVzK3KGQs9nUzuQd1aavaCY9PrFA/XcklDjjhUsDcIL2RizA8E0rjPRt 56tA== X-Gm-Message-State: AOAM530TH9s3pzLCnsGfm+fcBDx7+ttqKpZVJBYxXdpEY6HnYLzDle24 FYrVcEr1SDh8zSH3/MEl7zonnwNzb88fi17FcToxaA== X-Google-Smtp-Source: ABdhPJyXRzF2I+Ws0AWNK+Ok5vxMrH7xi3vhFQsySKA1MNuQTOhD4sxOfKp9BfmSDcXq2hOtiNe1J8xmD5Iusfo0dTY= X-Received: by 2002:aca:48d8:: with SMTP id v207mr5068681oia.48.1596124380496; Thu, 30 Jul 2020 08:53:00 -0700 (PDT) MIME-Version: 1.0 References: <20200716154114.10838-1-peter.maydell@linaro.org> <0f8b8fea-2bd0-7616-292b-8fb0f87cec75@redhat.com> <87k0ylvy0t.fsf@dusky.pond.sub.org> In-Reply-To: <87k0ylvy0t.fsf@dusky.pond.sub.org> From: Peter Maydell Date: Thu, 30 Jul 2020 16:52:49 +0100 Message-ID: Subject: Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id() To: Markus Armbruster Content-Type: text/plain; charset="UTF-8" Received-SPF: pass client-ip=2607:f8b0:4864:20::242; envelope-from=peter.maydell@linaro.org; helo=mail-oi1-x242.google.com X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. 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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, 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 , =?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 Thu, 30 Jul 2020 at 16:11, Markus Armbruster wrote: > > Peter Maydell writes: > > > On Tue, 28 Jul 2020 at 16:17, Eric Blake wrote: > >> > >> On 7/16/20 10:41 AM, Peter Maydell wrote: > >> > Add a documentation comment for qemu_get_thread_id(): since this > >> > is rather host-OS-specific it's useful if people writing the > >> > implementation and people thinking of using the function know > >> > what the purpose and limitations are. > >> > > >> > Signed-off-by: Peter Maydell > >> > --- > >> > Based on conversation with Dan on IRC, and prompted by the recent > >> > patch to add OpenBSD support. > >> > > >> > Q: should we document exactly what the thread-id value is for > >> > each host platform in the QMP documentation ? Somebody writing > >> > a management layer app should ideally not have to grovel through > >> > the application to figure out what they should do with the > >> > integer value they get back from query-cpus... > >> > > >> > include/qemu/osdep.h | 14 ++++++++++++++ > >> > 1 file changed, 14 insertions(+) > >> > >> Do we need a counterpart change... > >> > >> > > >> > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h > >> > index 4841b5c6b5f..8279f72e5ed 100644 > >> > --- a/include/qemu/osdep.h > >> > +++ b/include/qemu/osdep.h > >> > @@ -515,6 +515,20 @@ bool qemu_has_ofd_lock(void); > >> > > >> > bool qemu_write_pidfile(const char *pidfile, Error **errp); > >> > > >> > +/** > >> > + * qemu_get_thread_id: Return OS-specific ID of current thread > >> > + * > >> > + * This function returns an OS-specific identifier of the > >> > + * current thread. This will be used for the "thread-id" field in > >> > + * the response to the QMP query-cpus and query-iothreads commands. > >> > >> ...to the qapi definition of query-cpus and query-iothreads? > > > > Well, that was my question above. Currently the QAPI documentation > > says absolutely nothing about what the thread-id values mean > > for any host OS (beyond "ID of the underlying host thread"), which > > means that any management layer application needs to look in the > > implementation to find out what they actually are... > > ... which they will have to do to actually use it for the purpose we > have in mind, namely: > > >> > + * The intention is that a VM management layer application can then > >> > + * use it to tie specific QEMU vCPU and IO threads to specific host > >> > + * CPUs using whatever the host OS's CPU affinity setting API is. > >> > + * New implementations of this function for new host OSes should > >> > + * return the most sensible integer ID that works for that purpose. > >> > + * > >> > + * This function should not be used for anything else inside QEMU. > >> > + */ > > Do they? 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... > 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" ? thanks -- PMM