linux-kernel - Re: [linux-pm] [suspend/resume] Re: userspace notification from module

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Message-Id: <201001060005.17246.rjw@sisk.pl>
Date:	Wed, 6 Jan 2010 00:05:17 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Bartłomiej Zimoń <uzi18@...pl>
Cc:	linux-kernel@...r.kernel.org,
	Anders Eriksson <aeriksson@...tmail.fm>,
	Stefan Seyfried <stefan.seyfried@...glemail.com>,
	linux-pm@...ts.linux-foundation.org, danborkmann@...glemail.com,
	awalls@...ix.net
Subject: Re: [linux-pm] [suspend/resume] Re: userspace notification from module

On Tuesday 05 January 2010, Bartłomiej Zimoń wrote:
> Dnia 5 stycznia 2010 22:26 	Stefan Seyfried <stefan.seyfried@...glemail.com> napisał(a):
> > On Tue, 05 Jan 2010 10:07:06 +0100
> > Anders Eriksson <aeriksson@...tmail.fm> wrote:
> > 
> > > 
> > > rjw@...k.pl said:
> > > >> > I don't see a problem with this in principle, although I don't think signals
> > > >> > are very suitable for this particular purpose, because you need two-way
> > > >> > communication between the power manager and the processes it's going to
> > > >> > notify (because it has to wait for the processes to finish their preparations
> > > >> > and to tell it that they are ready). 
> > > 
> > > Wouldn't there need to be dependecy tracking for the userspace processes? A 
> > > process couldn't signal "done" until it know there's no more work to do, which 
> > > requires all other processes to finish up first.
> > 
> > No. 99% of the processes don't care about suspend. They don't need
> > notifications or anything.
> > The few that do care, register themselves with the power manager. They
> > get notified before suspend and the power manager might wait until they
> > tell him that they are ready.
> > A special case are processes that only want to inhibit suspend - the CD
> > burning application case - they just tell the power manager "I am
> > important and you must not suspend now". They do this even if there is
> > no suspend notification, and once they are done with the critical part
> > of their work, they remove their "inhibit flag".
> > 
> > This all works pretty well already, and is really not very complicated.
> 
> So pm could be very simple, and i think we don't need more.
> I want ask You how usualy such user (not root) process notification is done,
> You are talking about pm-utils right?

Well, I think you have some specific issue with pm-utils, but you're not
telling us what it is.  So, why exactly is pm-utils not suitable for your
needs?

Rafael
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