Re: [PATCH] namespaces: introduce sys_hijack (v4)

[Cedric Le Goater <clg-NmTC/0ZBporQT0dZR+AlfA@public.gmane.org>]

Serge E. Hallyn wrote:
> Quoting Serge E. Hallyn (serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org):
>> >From 945fe66259cd0cfdc2fe846287b7821e329a558c Mon Sep 17 00:00:00 2001
>> From: sergeh-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org <hallyn@kernel.(none)>
>> Date: Tue, 9 Oct 2007 08:30:30 -0700
>> Subject: [PATCH] namespaces: introduce sys_hijack (v4)
>>
>> Move most of do_fork() into a new do_fork_task() which acts on
>> a new argument, task, rather than on current.  do_fork() becomes
>> a call to do_fork_task(current, ...).
>>
>> Introduce sys_hijack (for x86 only so far).  It is like clone, but
>>  in place of a stack pointer (which is assumed null) it accepts a
>> pid.  The process identified by that pid is the one which is
>> actually cloned.  Some state - include the file table, the signals
>> and sighand (and hence tty), and the ->parent are taken from the
>> calling process.
>>
>> The effect is a sort of namespace enter.  The following program
>> uses sys_hijack to 'enter' all namespaces of the specified pid.
>> For instance in one terminal, do
>>
>> 	mount -t cgroup -ons /cgroup
>> 	hostname
>> 	  qemu
>> 	ns_exec -u /bin/sh
>> 	  hostname serge
>>           echo $$
>>             1073
>> 	  cat /proc/$$/cgroup
>> 	    ns:/node_1073
>>
>> In another terminal then do
>>
>> 	hostname
>> 	  qemu
>> 	cat /proc/$$/cgroup
>> 	  ns:/
>> 	hijack 1073
>> 	  hostname
>> 	    serge
>> 	  cat /proc/$$/cgroup
>> 	    ns:/node_1073
>>
>> sys_hijack is arch-dependent and is only implemented for i386 so far.
>>
>> Changelog:
>> 	Aug 23: send a stop signal to the hijacked process
>> 		(like ptrace does).
>> 	Oct 09: Update for 2.6.23-rc8-mm2 (mainly pidns)
>> 		Don't take task_lock under rcu_read_lock
>> 		Send hijacked process to cgroup_fork() as
>> 		the first argument.
>> 		Removed some unneeded task_locks.
> 
> Thanks to Cedric for finding an oops when using pid namespaces.  The
> following patch fixes the problem.

it works fine now.

Thanks !

C.