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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A96B1C433F5 for ; Thu, 28 Oct 2021 04:39:12 +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 52C3C61073 for ; Thu, 28 Oct 2021 04:39:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 52C3C61073 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]:42482 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mfxC3-0004ro-GQ for qemu-devel@archiver.kernel.org; Thu, 28 Oct 2021 00:39:11 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49806) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mfxAw-0003SD-Id for qemu-devel@nongnu.org; Thu, 28 Oct 2021 00:38:04 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:42360) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mfxAu-0001dk-Gn for qemu-devel@nongnu.org; Thu, 28 Oct 2021 00:38:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1635395879; 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=IwmvqbizbpFr8/0Zj7R41yyWHItp+jC5sgd9OHzAMvc=; b=bC+N0dsKLljL+4vzVGFacFn0K3DmOJdoFRyaTWuPp21ez2D7pc2vPsqY/la55Q+uEv1Qny dj696HwtXD6LqbVzisBDSwlF2yRUM9JO3Zt8gEKtBuY3mgRsLPbpe1Wj9JIeHue5FsuxfT wRoplfpWy2z4I6fe5VydyJyeZwdRle8= Received: from mail-lf1-f71.google.com (mail-lf1-f71.google.com [209.85.167.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-479-C0dRunJCMl6FBJnyAczWeA-1; Thu, 28 Oct 2021 00:37:57 -0400 X-MC-Unique: C0dRunJCMl6FBJnyAczWeA-1 Received: by mail-lf1-f71.google.com with SMTP id h21-20020a0565123c9500b003ffa23a0577so2291821lfv.18 for ; Wed, 27 Oct 2021 21:37:57 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=IwmvqbizbpFr8/0Zj7R41yyWHItp+jC5sgd9OHzAMvc=; b=T8VYzekrfhI7a2EXBnY4ta7pOsAIxQ1SNgbKeJF5ZeMfQ2duaIIbnylA1bCvuXBXug 8mKcnHjkcldJPrFn8Rhe7oPuZAtdFSmIxLi9nTkpgCHSbbz6NNO6TFHbpv+rrLyiKF2a Mj+Q+LEsvlPm63ZGra4I87Nf6CrBN4PNcSJ2zNNu3xeK++HJH74fS4JwRXaHXgFaC5Dk OQe+IFaRzmNz3qe47F2Fh6qEtnoiCQaN/AXVsM7xYRFs9vw441umz9YJ3ZVisMy/Ezsv o0bLtu4WJTKNYr6BCMG+UZvW6yPWNOMQH51lArb5h/+pTX+0mduOT5OuXbF4MwOrerVn bCLQ== X-Gm-Message-State: AOAM531TUoMXOLmWBJscYkdEZPVwGoV8xrL+R2IwWGhsdffGHQu6Cz6F FNC1ZDZL/ghWNGi+KnNINL2W3ZsZIHnwzqvbnlykjZdVo1SRGPRIPXHBluk4fhv/E57duy/IQst /Cx68+/4vmqbCOI5cX4oYKGsP5oe4vTg= X-Received: by 2002:a2e:a883:: with SMTP id m3mr2163108ljq.472.1635395876281; Wed, 27 Oct 2021 21:37:56 -0700 (PDT) X-Google-Smtp-Source: ABdhPJyF7yGRIw8BUbNLka+mKaKwBZ5zYPdbzLg/nhQLFjTq/TLFkgvOeCFSZ3pFlRxiI1Un4dCtKZk42pbXSikBVsw= X-Received: by 2002:a2e:a883:: with SMTP id m3mr2163088ljq.472.1635395876037; Wed, 27 Oct 2021 21:37:56 -0700 (PDT) MIME-Version: 1.0 References: <20211009075612.230283-1-leobras@redhat.com> <20211009075612.230283-4-leobras@redhat.com> <20211011193156.biedorxjetduaf7y@redhat.com> <87sfx6g55m.fsf@dusky.pond.sub.org> <87sfwl3h5i.fsf@dusky.pond.sub.org> In-Reply-To: <87sfwl3h5i.fsf@dusky.pond.sub.org> From: Leonardo Bras Soares Passos Date: Thu, 28 Oct 2021 01:37:58 -0300 Message-ID: Subject: Re: [PATCH v4 3/3] multifd: Implement zerocopy write in multifd migration (multifd-zerocopy) To: Markus Armbruster Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=lsoaresp@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Received-SPF: pass client-ip=216.205.24.124; envelope-from=lsoaresp@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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: =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= , Juan Quintela , Jason Wang , "Dr. David Alan Gilbert" , Peter Xu , qemu-devel , Eric Blake Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Oct 28, 2021 at 1:30 AM Markus Armbruster wrote: > > Leonardo Bras Soares Passos writes: > > [...] > > >> The general argument for having QAPI schema 'if' mirror the C > >> implementation's #if is introspection. Let me explain why that matters. > >> > >> Consider a management application that supports a range of QEMU > >> versions, say 5.0 to 6.2. Say it wants to use an QMP command that is > >> new in QEMU 6.2. The sane way to do that is to probe for the command > >> with query-qmp-schema. Same for command arguments, and anything else > >> QMP. > >> > >> If you doubt "sane", check out Part II of "QEMU interface introspection: > >> From hacks to solutions"[*]. > >> > >> The same technique works when a QMP command / argument / whatever is > >> compile-time conditional ('if' in the schema). The code the management > >> application needs anyway to deal with older QEMU now also deals with > >> "compiled out". Nice. > >> > >> Of course, a command or argument present in QEMU can still fail, and the > >> management application still needs to handle failure. Distinguishing > >> different failure modes can be bothersome and/or fragile. > >> > >> By making the QAPI schema conditional mirror the C conditional, you > >> squash the failure mode "this version of QEMU supports it, but this > >> build of QEMU does not" into "this version of QEMU does not support > >> it". Makes sense, doesn't it? > >> > >> A minor additional advantage is less generated code. > >> > >> > >> > >> [*] http://events17.linuxfoundation.org/sites/events/files/slides/armbru-qemu-introspection.pdf > >> > > > > This was very informative, thanks! > > I now understand the rationale about this choice. > > > > TBH I am not very used to this syntax. > > I did a take a peek at some other json files, and ended adding this > > lines in code, which compiled just fine: > > > > for : enum MigrationParameter > > {'name': 'multifd-zerocopy', 'if' : 'CONFIG_LINUX'}, > > > > for : struct MigrateSetParameters and struct MigrationParameters: > > '*multifd-zerocopy': { 'type': 'bool', 'if': 'CONFIG_LINUX' }, > > > > Is that enough? Is there any other necessary change? > > Looks good to me. > > The QAPI schema language is documented in docs/devel/qapi-code-gen.rst. Thanks for reviewing and for pointing this docs! > > If you're curious, you can diff code generated into qapi/ before and > after adding the 'if'. Good idea! > > > Thanks for reviewing and for helping out with this! > > My pleasure! > :) Best regards, Leo