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

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Message-ID: <4B41E318.4050809@gmail.com>
Date:	Mon, 04 Jan 2010 13:46:16 +0100
From:	Daniel Borkmann <danborkmann@...glemail.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Bartłomiej Zimoń <uzi18@...pl>,
	linux-kernel@...r.kernel.org, awalls@...ix.net,
	danborkmann@...glemail.com, linux-pm@...ts.linux-foundation.org,
	stern@...land.harvard.edu
Subject: Re: [suspend/resume] Re: userspace notification from module

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?

Best regards,
Daniel

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