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From: Zheng Chuan To: Steve 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: Message-ID: Date: Wed, 4 Aug 2021 17:30:05 +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: dggems706-chm.china.huawei.com (10.3.19.183) To dggpeml500005.china.huawei.com (7.185.36.59) X-CFilter-Loop: Reflected Received-SPF: pass client-ip=45.249.212.255; envelope-from=zhengchuan@huawei.com; helo=szxga08-in.huawei.com X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_MED=-2.3, 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" kindly ping？ On 2021/7/30 21:10, 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:) > -- Regards. Chuan