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    SubjectRe: [PATCH 0/2] Send a SIGCHLD to the init's pid namespace parent when reboot
    Quoting Oleg Nesterov (oleg@redhat.com):
    > On 08/14, Serge E. Hallyn wrote:
    > >
    > > Quoting Oleg Nesterov (oleg@redhat.com):
    > > > On 08/11, Daniel Lezcano wrote:
    > > > >
    > > > > In the case of a VPS, when we shutdown/halt/reboot the container, the
    > > > > reboot utility will invoke the sys_reboot syscall which has the bad
    > > > > effect to reboot the host.
    > > >
    > > > Stupid question. Can't sys_reboot() simply kill init (and thus the whole
    > > > pid_ns) in this case?
    > >
    > > The goal is to be able to distinguish a request for reboot from shutdown.
    > > If we just kill the init, then the parent of init (the container monitor)
    > > cannot restart the container to emulate reboot.
    >
    > OK, thanks.
    >
    > What if init reports the reason it was killed?
    >
    > Ignoring LINUX_REBOOT_CMD_CAD_/etc, I mean, roughly,
    >
    > - add "int reboot_cmd" into struct pid_namespace
    >
    > - sys_reboot(cmd) does
    >
    > if (!global_namespace) {
    > task_active_pid_ns(current)->reboot_cmd = cmd;
    > sigkill_my_init();
    > }
    >
    > - change zap_pid_ns_processes() to do
    >
    > if (pid_ns->reboot_cmd) // approximately
    > current->exit_state = pid_ns->reboot_cmd;
    >
    > Then its parent can look at status after wait(&status).

    That looks good to me. Daniel, is there a reason this wouldn't work?

    > Not that I think this is very nice, but signals are not reliable.
    > And once again, SIGCHLD doesn't queue. And, perhaps this doesn't
    > matter, but sys_reboot() sends SIGCHLD and returns -EPERM, this
    > can confuse the container.

    I think you're looking at an older (Aug 11) version. Daniel's newer
    patch should do the right thing (but I don't seem to have it in front
    of me atm)

    > In any case. If you want to send a signal, please do not introduce
    > SA_CLDREBOOT. Please do not play with ptrace or __wake_up_parent, this
    > is meaningless. Just fill siginfo and send SIGCHLD unconditionally.
    >
    > Oleg.

    Thanks for the help, Oleg.

    -serge


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