linux-kernel - Re: [PATCH] Kconfig: Update swsusp description

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Message-Id: <200703062142.28952.rjw@sisk.pl>
Date:	Tue, 6 Mar 2007 21:42:28 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Kconfig: Update swsusp description

Hi,

On Tuesday, 6 March 2007 10:41, Pavel Machek wrote:
> Hi!
> 
> > > > Index: linux-2.6.21-rc2/kernel/power/Kconfig
> > > > ===================================================================
> > > > --- linux-2.6.21-rc2.orig/kernel/power/Kconfig	2007-02-28 23:54:45.000000000 +0100
> > > > +++ linux-2.6.21-rc2/kernel/power/Kconfig	2007-03-04 11:50:48.000000000 +0100
> > > > @@ -81,30 +81,35 @@ config SOFTWARE_SUSPEND
> > > >  	bool "Software Suspend"
> > > >  	depends on PM && SWAP && ((X86 && (!SMP || SUSPEND_SMP)) || ((FRV || PPC32) && !SMP))
> > > >  	---help---
> > > > +	  Enable the suspend to disk (STD) functionality.
> > > >  
> > > > +	  You can suspend your machine with 'echo disk > /sys/power/state'.
> > > > +	  Alternatively, you can use the additional userland tools available
> > > > +	  from <http://suspend.sf.net>.
> > > > +
> > > > +	  In principle it does not require ACPI or APM, although for example
> > > > +	  ACPI will be used if available.
> > > > +
> > > > +	  It creates an image which is saved in your active swap. Upon the next
> > > >  	  boot, pass the 'resume=/dev/swappartition' argument to the kernel to
> > > 
> > > Actually, these days resume=... on kernel command line needs to be
> > > there for suspend, too, IIRC.
> > 
> > I didn't change this line, so?
> 
> So I should go and fix it ;-). (I'm now overloaded with email sorry
> for being terse.)
> 
> Can we do something like
> 
> +	  Enable the suspend to disk (STD) functionality.
> +	  In principle it does not require any support from BIOS, although 
> +	  ACPI will be used if available.
> 
> +	  You can suspend your machine with 'echo disk >
> +	  /sys/power/state' after placing resume=/dev/swappartition on
> +	  kernel command line.
> +	  Alternatively, you can use the additional userland tools available
> +	  from <http://suspend.sf.net>.
> 
> (and remove ...upon next boot... section).

Generally, why not, but I think Andrew has already pushed the patch to Linus,
so perhaps we can apply the changes on top of it?

> > > > +	  Right now you may boot without resuming and resume later but in the
> > > > +	  meantime you cannot use the swap partition(s)/file(s) involved in
> > > > +	  suspending.  Also in this case you must not use the
> > > 
> > > I'd prefer not to encourage this use. It has too many traps ready for
> > > people.
> > 
> > But IMHO there should be a warning that if you boot without resuming, make sure
> > you'll not resume after the next reboot or bad things will happen.
> 
> +	It is possible to boot without resuming and resume later but
> +	if you access any partitions/files used by suspended kernel,
> +	you'll probably loose your data. See ... for details.

Well, I think "access" is too weak here.  IMO we should say something like
"if you have booted without resuming and any journaled filesystems used before
the suspend have been mounted, you MUST NEVER EVER attempt to resume from the
'old' image.  In that case make sure the image is destroyed by running 'mkswap'
against the swap partition/file that contains it."

Greetings,
Rafael
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