linux-kernel - Re: [RFC v12][PATCH 01/14] Create syscalls: sys_checkpoint, sys

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Date:	Wed, 14 Jan 2009 17:31:54 -0500
From:	Oren Laadan <orenl@...columbia.edu>
To:	balbir@...ux.vnet.ibm.com
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...l.org>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-api@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Serge Hallyn <serue@...ibm.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Mike Waychison <mikew@...gle.com>
Subject: Re: [RFC v12][PATCH 01/14] Create syscalls: sys_checkpoint,	sys_restart



Balbir Singh wrote:
> * Oren Laadan <orenl@...columbia.edu> [2008-12-29 04:16:14]:
> 
>> Create trivial sys_checkpoint and sys_restore system calls. They will
>> enable to checkpoint and restart an entire container, to and from a
>> checkpoint image file descriptor.
>>
>> The syscalls take a file descriptor (for the image file) and flags as
>> arguments. For sys_checkpoint the first argument identifies the target
>> container; for sys_restart it will identify the checkpoint image.
>>
>> A checkpoint, much like a process coredump, dumps the state of multiple
>> processes at once, including the state of the container. The checkpoint
>> image is written to (and read from) the file descriptor directly from
>> the kernel. This way the data is generated and then pushed out naturally
>> as resources and tasks are scanned to save their state. This is the
>> approach taken by, e.g., Zap and OpenVZ.
>>
>> By using a return value and not a file descriptor, we can distinguish
>> between a return from checkpoint, a return from restart (in case of a
>> checkpoint that includes self, i.e. a task checkpointing its own
>> container, or itself), and an error condition, in a manner analogous
>> to a fork() call.
>>
>> We don't use copyin()/copyout() because it requires holding the entire
> 
>               ^^^^^^^^^^^^^^^^^^^ Do you mean get_user_pages(),
> copy_to/from_user()?

Yes, I meant copy_to/from_user() ...

Oren.


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