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

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Message-Id: <201001042045.44372.rjw@sisk.pl>
Date:	Mon, 4 Jan 2010 20:45:44 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Daniel Borkmann <danborkmann@...glemail.com>
Cc:	Bartłomiej Zimoń <uzi18@...pl>,
	linux-kernel@...r.kernel.org, awalls@...ix.net,
	linux-pm@...ts.linux-foundation.org, stern@...land.harvard.edu
Subject: Re: [suspend/resume] Re: userspace notification from module

On Monday 04 January 2010, Daniel Borkmann wrote:
> Rafael J. Wysocki wrote:
> > On Monday 04 January 2010, Bartłomiej Zimoń wrote:
> >> And what do You think about sending extra signals to processes?
> > 
> > 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).
> 
> Again, just to abandon some thoughts... do you really need that "two-way
> communication"? I mean if the kernel delivers that specific signal to
> the process/task_struct [do_signal():handle_signal()] it has to save the
> original execution context that will later on be restored after the
> non-default signal handling function returns. This is our ACK /
> notification for the successful return of the programs "suspend
> handler". The kernel module (if such exists) could be notified about
> that for instance by a simple notifier hook within kernelspace. I mean
> if I see this right, the "two-way" is just for the ACK isn't it?

_If_ the kernel sends the signals, which is not I think should be done.

Please keep that in the user space.  Really.

I don't see _any_ good reason for putting such things into the kernel.

Rafael
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