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=-5.4 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,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 569AAC4338F for ; Thu, 5 Aug 2021 14:10:53 +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 E93396113B for ; Thu, 5 Aug 2021 14:10:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org E93396113B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:60938 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mBe5E-0003Ql-5l for qemu-devel@archiver.kernel.org; Thu, 05 Aug 2021 10:10:52 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49326) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mBdzJ-0003wk-5u for qemu-devel@nongnu.org; Thu, 05 Aug 2021 10:04:45 -0400 Received: from szxga03-in.huawei.com ([45.249.212.189]:2201) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mBdzG-0004kP-0i for qemu-devel@nongnu.org; Thu, 05 Aug 2021 10:04:44 -0400 Received: from dggemv711-chm.china.huawei.com (unknown [172.30.72.55]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4GgVbV3bsVz7tg0; Thu, 5 Aug 2021 21:59:34 +0800 (CST) Received: from dggpeml500005.china.huawei.com (7.185.36.59) by dggemv711-chm.china.huawei.com (10.1.198.66) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Thu, 5 Aug 2021 22:04:26 +0800 Received: from [10.174.186.51] (10.174.186.51) by dggpeml500005.china.huawei.com (7.185.36.59) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Thu, 5 Aug 2021 22:04:26 +0800 Subject: Re: [PATCH V5 00/25] Live Update [restart] : fork mode? To: Steven Sistare , Qemu Developers , "Dr. David Alan Gilbert" , "Juan Quintela" , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , Alex Williamson , "Paolo Bonzini" , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Xiexiangyou References: From: Zheng Chuan Message-ID: <998c8c53-a4ee-b25f-62f9-47179d4a81bc@huawei.com> Date: Thu, 5 Aug 2021 22:04:25 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.186.51] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To dggpeml500005.china.huawei.com (7.185.36.59) X-CFilter-Loop: Reflected Received-SPF: pass client-ip=45.249.212.189; envelope-from=zhengchuan@huawei.com; helo=szxga03-in.huawei.com X-Spam_score_int: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 5.0 requ) BAYES_00=-1.9, NICE_REPLY_A=-0.132, RCVD_IN_DNSWL_MED=-2.3, 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi, Steve. On 2021/8/5 4:50, Steven Sistare wrote: > On 7/30/2021 9:10 AM, Zheng Chuan wrote: >> Hi, Steve >> I have saw the discussion about the fork+exec mode below: >> https://www.mail-archive.com/qemu-devel@nongnu.org/msg815956.html >> >> And I am still very curious and I want to discuss about the possibility to support both fork+exec and exec in cpr framework. >> >> 1.Why >> fork+exec could have some advantages and also drawbacks versus execvp() directly. >> Advantages >> i) fork+exec give the chance to fallback to original process even after we do exec which is important for workload seamless if any error happens. >> ii) smaller downtime since we could remove the vm_start() downtime out of the frozen window. >> Drawbacks >> i）need more codes to handle including fork，address/ports conflict between parent and child. >> ii）more complex life cycle management for the two processes. >> >> 2.How >> The cpr framework is flexible and scalable, and maybe we can make use of most codes to support both execvp and fork+exec mode. >> However, we may need to do more work compared to execvp method. >> i) do fork mode in a thread like migration thread >> ii) make parent and child talk to each other through socket or anonymous pipe >> iii）make use of sharing mechanism of fds in cpr framework including memfd, vfio and devices fds >> iv）deal with the conflict about the socket address and port like vnc （do by reuse port and pass the different args by cprexec） >> v) do life cycle managements for two qemu processes and need parent exit and reconnection for the child at last by the management service >> >> Please tell me if I am missing something important:) > > Hi Zheng, that list sounds about right. However, additional kernel changes would be needed to > change ownership of the vfio device descriptors. The vfio module records the mm of the creating > process, and does not allow other processes to unmap ranges. Also, the mm->locked_vm would > need to be transferred to the new process. > Oh，That's right. Maybe we could update them along with VFIO_DMA_MAP_FLAG_VADDR. > Fork+exec could be a new mode to the cprsave command. > Yeah, I would be very happy to see it in the future:) > - Steve > . > -- Regards. Chuan