From: Nigel Cunningham <nigel@suspend2.net>
Organization: Suspend2.net
To: Pavel Machek <pavel@ucw.cz>
Subject: Re: Which is simpler? (Was Re: [Suspend2-devel] Re: [ 00/10] [Suspend2] Modules support.)
Date: Wed, 8 Feb 2006 09:17:19 +1000
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Cc: "Rafael J. Wysocki" <rjw@sisk.pl>, Bojan Smojver <bojan@rexursive.com>,
       Lee Revell <rlrevell@joe-job.com>, linux-kernel@vger.kernel.org,
       suspend2-devel@lists.suspend2.net
References: <20060201113710.6320.68289.stgit@localhost.localdomain> <200602080814.02894.nigel@suspend2.net> <20060207230510.GF2753@elf.ucw.cz>
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Hi again.

On Wednesday 08 February 2006 09:05, Pavel Machek wrote:
> Hi!
>=20
> > > > # cat /sys/power/disk_method
> > > > swsusp uswsusp suspend2
> > > > # echo uswsusp > /sys/power/disk_method
> > > > # echo > /sys/power/state
> > > >=20
> > > > Is there a big problem with that, which I've missed?
> > >=20
> > > Userland suspend is driven by the suspending application which only=20
calls
> > > the kernel to do things it cannot do itself, like freezing (the=20
other)
> > > processes, snapshotting the system etc.  We use the /dev/snapshot
> > > device and the ioctl()s in there, so no sysfs files are needed for=20
that.
> > > It's independent and can coexist with the existing sysfs interface
> > > just fine.
> >=20
> > Yes, but how are you going to get it started from (say) klaptop, which=
=20
only=20
> > knows "echo disk > /sys/power/state" as the way of starting a suspend?=
=20
I'm=20
> > suggesting that we create a means whereby the issue of how to start a=20
> > cycle could be separated from what implementation is used to do the=20
work.=20
> > That is, a simple extension at the start of the disk specific code that=
=20
> > starts swsusp, uswsusp or suspend2 depending upon what you want. Maybe=
=20
I=20
> > should just prepare a patch.
>=20
> Please do not patch kernel for that.
>=20
> Proper solution is probably creating s2disk program/script, and teach
> kpowersave/klaptop/etc. to just use it. Then s2disk can detect best
> method to use ... and then just do it. You already have suitable
> script, but I'm not sure what its name is.

It occured to me as soon as I sent the last email (don't you hate that!)
that I'd forgotten the original impetus: backwards compatibility. If all
of the methods of suspending can be started with

"echo disk > /sys/power/state"

, your backwards compatability issue that you expressed concern about=20
earlier in this discussion is addressed. So, I'm not sure that dropping the
idea is the right thing to do.

Regards,

Nigel

=2D-=20
See our web page for Howtos, FAQs, the Wiki and mailing list info.
http://www.suspend2.net                IRC: #suspend2 on Freenode

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