From: Ed Tomlinson <tomlins@cam.org>
Organization: me
To: Bernard Blackham <bernard@blackham.com.au>
Subject: Re: A possible idea for Linux: Save running programs to disk
Date: Sun, 2 Oct 2005 08:57:26 -0400
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Cc: lokum spand <lokumsspand@hotmail.com>, linux-kernel@vger.kernel.org
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Hi,

Looks like this can be done in user space...

Bernard, Is there any kernel api that adding would make cryopid
more dependable/cleaner?

Ed Tomlinson

On Sunday 02 October 2005 00:53, Bernard Blackham wrote:
> On Sat, Oct 01, 2005 at 01:30:22PM -0800, lokum spand wrote:
> > Suppose Linux could save the total state of a program to disk, for
> > instance, imagine a program like mozilla with many open windows. I give
> > it a SIGNAL-SAVETODISK and the process memory image is dropped to a
> > file. I can then turn off the computer and later continue using the
> > program where I left it, by loading it back into memory.
> 
> www.checkpointing.org lists several solutions for this.
> 
> I'm the author of CryoPID[1] - it's a checkpointing program that
> allows you to save the state of a process to a file without any
> prior thought when linking or running the process. It won't handle
> an entire mozilla process, but single-threaded console-based apps
> are quite feasible.  Migration between machines works too - 2.6 to
> 2.6 works, 2.4 to 2.4 works, 2.6 to 2.4 works, and 2.4 to 2.6 mostly
> works with some TLS emulation (which might be incomplete, but can
> always be improved).
> 
> Open files are reopened. Opened temporary files (unlinked) could
> potentially be restored by scraping the contents out of the file
> while the process in question has it open.
> 
> Networking isn't too bad really so long as you keep the same IP. TCP
> sockets can be handled by tcpcp[2] which is already supported by
> CryoPID. UDP sockets are pretty trivial, but not yet done. For both
> of these to be reliable though, there needs to be some sort of
> arrangement to drop packets on these connections whilst they are
> suspended and not have the kernel send an RST back. (Thinking a
> daemon that drives some iptables).
> 
> Unix sockets are indeed trickier. Mostly this is for X applications,
> and for this I'm actually looking towards toolkit-based solutions as
> apps can't be expected to deal with things like colour depth changes
> and so on.  Gtk+ can already migrate applications between displays,
> with the only issue being that not all the resources tied to the
> original X server are freed, so you can't lose it. This is scheduled
> to be fixed for Gtk+ 2.10 though, so I'm holding out hope for this.
> 
> Multithreading or even multiple processes will be a fun one though.
> Ditto for shared memory and other IPC stuff.  Determined that it's
> possible, just not sure how yet. :)
> 
> As for portability, it was written for x86 and has been ported to
> AMD64, and I'm also in the middle of porting it to sparc. (ppc and
> alpha planned too).
> 
> Yes, it has to do some pretty vile things to avoid modifying the
> kernel or userspace programs, but it's quite suitable for doing
> things like backing up your irssi sessions hourly, saving
> computational jobs across a reboot or moving them to another
> machine, or showing off features of an application.
> 
> Bernard.
> 
> [1] http://cryopid.berlios.de/
> [2] http://tcpcp.sf.net/
> 
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