linux-kernel - prctl(PR_SET

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Message-Id: <20130218013954.28FCF59206F@miso.sublimeip.com>
Date:	Mon, 18 Feb 2013 12:39:54 +1100 (EST)
From:	u3557@...o.sublimeip.com (Amnon Shiloh)
To:	oleg@...hat.com (Oleg Nesterov)
Cc:	palves@...hat.com (Pedro Alves),
	dvlasenk@...hat.com (Denys Vlasenko),
	jan.kratochvil@...hat.com (Jan Kratochvil),
	gorcunov@...nvz.org (Cyrill Gorcunov),
	xemul@...allels.com (Pavel Emelyanov),
	rostedt@...dmis.org (Steven Rostedt),
	fweisbec@...il.com (Frederic Weisbecker),
	mingo@...hat.com (Ingo Molnar),
	a.p.zijlstra@...llo.nl (Peter Zijlstra),
	linux-kernel@...r.kernel.org
Subject: prctl(PR_SET_MM)

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)

Thank you,
Amnon.
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