On Wed, Aug 17, 2011 at 15:05, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > On 08/17, Oleg Nesterov wrote: >> On 08/16, Andrew Morton wrote: >> > From: Lennart Poettering <lennart@xxxxxxxxxxxxxx> >> > >> > Userspace service managers/supervisors need to track their started >> > services. Many services daemonize by double-forking and get implicitely >> > re-parented to PID 1. The process manager will no longer be able to >> > receive the SIGCHLD signals for them. >> > >> > With this prctl, a service manager can mark itself as a sort of 'sub-init' >> > process, able to stay as the parent process for all processes created by >> > the started services. All SIGCHLD signals will be delivered to the >> > service manager. >> >> I try to never argue with the new features. But to be honest, this >> doesn't look very good to me. >> >> OK, a service manager M does prctl(PR_SET_CHILD_REAPER), then it forks >> a service X which forks another child C and exits. Then C exits and >> notifies M. >> >> But. How can M know that the service X should be restarted? It only >> knows the pid. What if wait(WEXITED) succeeds because C in turn does >> fork + exit? What M has 2 or more services? > > Also. I am almost sure I have already reviewed a very similar patch > a long ago. It's almost the same. > Ungortunately, I can't find the previous discussion, and > I can't recall why that patch was not accepted. We've just been busy with other things. But now that systemd will not only be PID 1 but also the process parent for every user logged into the system, we need this functionality. > But, I seem to remember, that patch cleared ->child_reaper on exec, I don't think he original patch did. > I think this makes sense. Why would it? Systemd can serialize its state and properly re-exec itself as many times as needed during its lifetime. Why would the kernel take something away from a process, which it explicitly asked for? > And I am not sure about security. No, I do not see any problems, just > I don't know. Say, should we check the creds during reparenting? I > dunno. Hmm, I don't see why that would be necessary. It's just one of our parents that aks for our signals. Kay -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
