Mike Waychison <mikew@xxxxxxxxxx> writes: >> all of this conversation originally started. I am happy to set the starting >> pid to 2 to avoid confusion on that point. > > I wasn't really taking into consideration the notion of a 'lightweight' pid > namespace that didn't have a 'container-init' process. I know that was something the Vserver guys were do today. They have something that shows up as pid 1 but they don't really have a process there. >> One of the other problems with changing the pid is that user space in general >> glibc in particular can not cope with the pid of a process changing. >> >> My memories are foggy at the moment but I do know that on the several occasions >> we have looked at unshare of the pid namespace it has failed due to kernel issues. >> I also remember I was close to having resolved the issues of unsharing the pid >> namespace if we did not change the pid of processing calling unshare. > > Do you have pointers to discussions about these issues? Not better than the containers list archives. >> You did not answer my question. I don't quite see how you were envisioning >> using unsharing the pid namespace as part of restart so I can't tell if my >> proposed semantics would work for that case. > > Well, one way to look at doing restart with nested namespaces would be to have > userland go off and begin by rebuilding the process tree. While rebuilding, any > given process being recreated would need to have the same pid in the parenting > pid namespace (the outer most namespace in the container). It would need to > know if it 'got' the right pid, and if so, would then create the new child pid > namespace. Requiring CLONE_NEWPID set on each and every clone(2) [*] would > certainly be possible, as long as we had some way for the task being created to > know what it's parent namespace pid is. I guess this could be done by a shared > memory segment shared between the parent and child of the clone as well, though > it doesn't seem as clear-cut to me. > > > > [*] Yes, I'm dancing around the clone_with_pid issue.. Ok. I see what you are trying to accomplish with this and honestly I think it is silly. We should start the threads we need in the kernel, and if we need to run clone_pid fine. I am not comfortable exporting clone_with_pid to user space. As for the implementation of allocating a struct pid with a certain set of pid values. I expect we can do that easily enough by refactoring the pid allocator to be passed in the min/max pid to allocate from, and have a special case that passes in a different set of min/max values so we can allocate just the pid we need. If the primary use for a userspace interface is restart I feel we are doing it wrong. Eric _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
