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=-3.6 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 D669DC2D0A8 for ; Mon, 28 Sep 2020 10:43:11 +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 173322075A for ; Mon, 28 Sep 2020 10:43:10 +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="hrIXOG2q" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 173322075A 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]:34694 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kMqcg-0007Fy-3z for qemu-devel@archiver.kernel.org; Mon, 28 Sep 2020 06:43:10 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:43514) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kMqby-0006QC-On for qemu-devel@nongnu.org; Mon, 28 Sep 2020 06:42:26 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:34140) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kMqbw-0006CQ-OE for qemu-devel@nongnu.org; Mon, 28 Sep 2020 06:42:26 -0400 Dkim-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1601289743; 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: in-reply-to:in-reply-to:references:references; bh=v0X7vSvNxXeBXTHcC1rQ4ded5Y8jHTSaXxF7/lALPtk=; b=hrIXOG2q0w8wlc8u94/qLP2mPHwcRhux3D+kp815QgKwBFxw1Dy9wVBs5ExSSX7GC60cVL WumrIooodLAFZlhjhg59tQ5lsvLCBWW5f7WjbwWPttZQuGZLRfsZesaM5DKWAbOlts+q8U qaLQKJAtJAiiQHuyo+u0zrAGhqZ0d7U= 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-505-d4n_AqgHMuSVm2Bp-SsaSg-1; Mon, 28 Sep 2020 06:42:21 -0400 X-MC-Unique: d4n_AqgHMuSVm2Bp-SsaSg-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 76FB58027E1; Mon, 28 Sep 2020 10:42:20 +0000 (UTC) Received: from linux.fritz.box (ovpn-114-193.ams2.redhat.com [10.36.114.193]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EF98B5D9CA; Mon, 28 Sep 2020 10:42:15 +0000 (UTC) Date: Mon, 28 Sep 2020 12:42:14 +0200 From: Kevin Wolf To: Markus Armbruster Subject: Re: [PATCH v7 07/13] monitor: Make current monitor a per-coroutine property Message-ID: <20200928104214.GE5451@linux.fritz.box> References: <20200909151149.490589-1-kwolf@redhat.com> <20200909151149.490589-8-kwolf@redhat.com> <874ko0o0jv.fsf@dusky.pond.sub.org> <20200925152307.GF5731@linux.fritz.box> <87sgb2l4wb.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87sgb2l4wb.fsf@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/28 03:29:35 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -36 X-Spam_score: -3.7 X-Spam_bar: --- X-Spam_report: (-3.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.576, 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_H5=-1, RCVD_IN_MSPIKE_WL=-0.01, 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-block@nongnu.org, marcandre.lureau@gmail.com, qemu-devel@nongnu.org, stefanha@redhat.com, dgilbert@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 28.09.2020 um 09:47 hat Markus Armbruster geschrieben: > Kevin Wolf writes: > > > Am 14.09.2020 um 17:11 hat Markus Armbruster geschrieben: > >> Kevin Wolf writes: > >> > >> > This way, a monitor command handler will still be able to access the > >> > current monitor, but when it yields, all other code code will correctly > >> > get NULL from monitor_cur(). > >> > > >> > This uses a hash table to map the coroutine pointer to the current > >> > monitor of that coroutine. Outside of coroutine context, we associate > >> > the current monitor with the leader coroutine of the current thread. > >> > >> In qemu-system-FOO, the hash table can have only these entries: > >> > >> * (OOB) One mapping @mon_iothread's thread leader to a QMP monitor, while > >> executing a QMP command out-of-band. > >> > >> * (QMP-CO) One mapping @qmp_dispatcher_co (a coroutine in the main > >> thread) to a QMP monitor, while executing a QMP command in-band and in > >> coroutine context. > >> > >> * (QMP) One mapping the main thread's leader to a QMP monitor, while > >> executing a QMP command in-band and out of coroutine context, in a > >> bottom half. > >> > >> * (HMP) One mapping the main thread's leader to an HMP monitor, while > >> executing an HMP command out of coroutine context. > >> > >> * (HMP-CO) One mapping a transient coroutine in the main thread to an > >> HMP monitor, while executing an HMP command in coroutine context. > >> > >> In-band execution is one command after the other. > >> > >> Therefore, at most one monitor command can be executing in-band at any > >> time. > >> > >> Therefore, the hash table has at most *two* entries: one (OOB), and one > >> of the other four. > >> > >> Can you shoot any holes into my argument? > > > > I think with human-monitor-command, you can have three mappings: > > > > 1. The main thread's leader (it is a non-coroutine QMP command) to the > > QMP monitor > > This is (QMP). > > > 2. With a coroutine HMP command, one mapping from the transient HMP > > coroutine to the transient HMP monitor (with a non-coroutine HMP > > command, we'd instead temporarily change the mapping from 1.) > > This is (HMP-CO). > > > 3. The OOB entry > > This is (OOB). > > To get 1. (QMP) and 2, (HMP-CO) at the same time, the in-band, > non-coroutine QMP command needs to execute interleaved with the in-band, > coroutine HMP command. > > Such an interleaving contradicts "In-band execution is one command after > the other", which is a fundamental assumption in-band commands may make. > If the assumption is invalid, we got a problem. Is it? Interleaving, or rather executing another command in the middle of its implementation is the very purpose of human-monitor-command (which is what I was talking about, so "the in-band non-coroutine QMP command" is a very specific one). It's the only command I can think of that is exceptional in this way and would lead to three mappings. Kevin