linux-kernel - Re: [PATCH 0/2] Send a SIGCHLD to the init's pid namespace parent when reboot

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Date:	Mon, 15 Aug 2011 19:50:02 +0200
From:	Daniel Lezcano <daniel.lezcano@...e.fr>
To:	"Serge E. Hallyn" <serge@...lyn.com>
CC:	Oleg Nesterov <oleg@...hat.com>, akpm@...ux-foundation.org,
	bonbons@...ux-vserver.org, containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Send a SIGCHLD to the init's pid namespace parent
 when reboot

On 08/15/2011 07:39 PM, Serge E. Hallyn wrote:
> Quoting Oleg Nesterov (oleg@...hat.com):
>> On 08/14, Serge E. Hallyn wrote:
>>> Quoting Oleg Nesterov (oleg@...hat.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?

No, it is an alternative we can try. Oleg raise a good point about the
SIGCHLD not being queue.
Let me write this patch and test it.

  -- Daniel


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