Re: [PATCH 1/1][V5] Add reboot_pid_ns to handle the reboot syscall

[Daniel Lezcano]

On 02/03/2012 01:10 AM, Andrew Morton wrote:
> On Thu,  5 Jan 2012 10:06:50 +0100
> Daniel Lezcano<daniel.lezcano@xxxxxxx>  wrote:
>
> > In the case of a child pid namespace, rebooting the system does not
> > really makes sense. When the pid namespace is used in conjunction
> > with the other namespaces in order to create a linux container, the
> > reboot syscall leads to some problems.
> >
> > A container can reboot the host. That can be fixed by dropping
> > the sys_reboot capability but we are unable to correctly to poweroff/
> > halt/reboot a container and the container stays stuck at the shutdown
> > time with the container's init process waiting indefinitively.
> >
> > After several attempts, no solution from userspace was found to reliabily
> > handle the shutdown from a container.
> >
> > This patch propose to make the init process of the child pid namespace to
> > exit with a signal status set to : SIGINT if the child pid namespace called
> > "halt/poweroff" and SIGHUP if the child pid namespace called "reboot".
> > When the reboot syscall is called and we are not in the initial
> > pid namespace, we kill the pid namespace for "HALT", "POWEROFF", "RESTART",
> > and "RESTART2". Otherwise we return EINVAL.
> >
> > Returning EINVAL is also an easy way to check if this feature is supported
> > by the kernel when invoking another 'reboot' option like CAD.
> >
> > By this way the parent process of the child pid namespace knows if
> > it rebooted or not and can take the right decision.
> Looks OK, although the comments need help.  Is the below still true?

Yes, thanks for fixing this.

> Do you think it would be feasible to put your testcase into
> tools/testing/selftests?  I'm thinking "no", because running the test
> needs elevated permissions and might reboot the user's machine(!).

Yes, right. I don't think the user will be happy with that. 
Unfortunately, I don't see how to test this feature without falling into 
a reboot on failure. On the other side, this very specific feature is 
used in the container environment and if it fails that will be spotted 
immediately and fixed. So I don't think that does make sense to add this 
test in tools/testing/selftests.

[ ... ]

>   	gid_t pid_gid;
>   	int hide_pid;
> +	int reboot;
>   };
> This was particuarly distressing.  The field was poorly named and other
> people forgotting to document their data structures doesn't mean that
> we should continue to do this!

Thanks again for adding the description. I will take care next time to 
add a simple description when the field name is not self-explicit or 
ambiguous.

  -- Daniel
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