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
