Re: [PATCH V5 00/25] Live Update [restart] : fork mode?

[Zheng Chuan]

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