linux-kernel - Re: Back to the future.

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Message-Id: <200704272326.58964.rjw@sisk.pl>
Date:	Fri, 27 Apr 2007 23:26:58 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pekka Enberg <penberg@...helsinki.fi>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Back to the future.

On Friday, 27 April 2007 14:49, Pavel Machek wrote:
> Hi!
> 
> > > * Doing things in the right order? (Prepare the image, then do the
> > > atomic copy, then save).
> > 
> > I'd actually like to discuss this a bit..
> > 
> > I'm obviously not a huge fan of the whole user/kernel level split and 
> > interfaces, but I actually do think that there is *one* split that makes 
> > sense:
> > 
> >  - generate the (whole) snapshot image entirely inside the kernel
> > 
> >  - do nothing else (ie no IO at all), and just export it as a single image 
> >    to user space (literally just mapping the pages into user space). 
> >    *one* interface. None of the "pretty UI update" crap. Just a single 
> >    system call:
> > 
> > 	void *snapshot_system(u32 *size);
> > 
> >    which will map in the snapshot, return the mapped address and the size 
> >    (and if you want to support snapshots > 4GB, be my guest, but I suspect 
> >    you're actually *better* off just admitting that if you cannot shrink 
> >    the snapshot to less than 32 bits, it's not worth doing)
> 
> I think this is very similar to current uswsusp design; except that we
> are using read on /dev/snapshot to read the snapshot (not memory
> mapping) and that we freeze the system

Yes, it seems so.

> (because I do not think killall _SIGSTOP is enough).

Agreed.

Greetings,
Rafael
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