Messages in this thread | | | Date | Mon, 15 Aug 2011 16:47:44 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 0/2] Send a SIGCHLD to the init's pid namespace parent when reboot |
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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).
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.
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.
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