linux-kernel - Re: prctl(PR_SET

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Date:	Sun, 17 Feb 2013 21:44:07 -0800
From:	Randy Dunlap <rdunlap@...radead.org>
To:	u3557@...lix.com.au
CC:	Amnon Shiloh <u3557@...o.sublimeip.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Pedro Alves <palves@...hat.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Jan Kratochvil <jan.kratochvil@...hat.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: prctl(PR_SET_MM)

On 02/17/13 17:39, Amnon Shiloh wrote:
> Hello,
> 
> The code in "kernel/sys.c" provides the "prctl(PR_SET_MM)" function,
> which is the only way a process can set or modify the following 11
> per-process fields:
> 
>  	start_code, end_code, start_data, end_data, start_brk, brk,
>  	start_stack, arg_start, arg_end, env_start, env_end.
> 
> Being able to set those fields is important, even crucial,
> for any conceivable user-level checkpointing software, as
> well as for migrating processes between different computers.
> 
> Unfortunately, this code (essentially "prctl_set_mm()") is presently
> enclosed in "#ifdef CONFIG_CHECKPOINT_RESTORE" which is configured
> as "default n" in "init/Kconfig".  Many system-administrators who
> may like to have a checkpoint/restore or process-migration facility,
> but use standard pre-packaged kernels, find the requirement to
> configure and compile their own non-standard kernel difficult or
> too prohibitive.
> 
> Would it be possible to have this code enabled by default?
> 
> This could be done in one of 4 ways:
> 1) Having CONFIG_CHECKPOINT_RESTORE enabled by default; or
> 2) Releasing this code from the "#ifdef CONFIG_CHECK_RESTORE"; or
> 3) Placing this code within a different kernel-configuration option
>    (say "CONFIG_BASIC_CHECKPOINTING") that is enabled by default; or
> 4) Placing this code under a dual #if, so instead of:
>    #ifdef CONFIG_CHECKPOINT_RESTORE
> 	   have:
>    #if defined(CONFIG_CHECKPOINT_RESTORE) || defined(CONFIG_BASIC_CHECKPOINTING)


This is basically a distro issue.  Distros can choose to enable
this code by default, but the Linux kernel that Linus maintains does
not need to enable it.


-- 
~Randy
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