linux-kernel - RE: [linux-pm] Re: Hibernation considerations

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Date:	Tue, 24 Jul 2007 21:26:35 +0800
From:	"Huang, Ying" <ying.huang@...el.com>
To:	"Alan Stern" <stern@...land.harvard.edu>, <david@...g.hm>
Cc:	"Jeremy Maitin-Shepard" <jbms@....edu>,
	"Milton Miller" <miltonm@....com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"LKML" <linux-kernel@...r.kernel.org>,
	"linux-pm" <linux-pm@...ts.linux-foundation.org>,
	<nigel@...el.suspend2.net>, "Pavel Machek" <pavel@....cz>
Subject: RE: [linux-pm] Re: Hibernation considerations

>From: Alan Stern [mailto:stern@...land.harvard.edu]
>It can't.  Indeed, in the absence of a freezer, user threads will need
>devices (more accurately, will submit I/O requests for devices) that
>have to be kept quiescent or low-power.  Drivers will need to delay
>those requests until the devices are returned to full operation.
>
>That's exactly what I've been saying all along: Drivers will need to
>be changed to delay I/O requests, if there is no freezer.

If it is a too big work to implement "delaying I/O requests" for every
driver, is it possible to implement it as follow:

1. It is triggered to suspend to RAM/DISK.
2. Replace the driver related syscall entries (such as sys_read,
sys_write, sys_ioctl, etc) in sys_call_table with special wrapper
entries provided by "suspend to RAM/DISK" subsystem, which will delay
I/O requests if appropriate.
3. When devices are quiesced, they are put into "low power" state and
system is put into suspend state; or the image is written to disk
(through snapshot/uswsusp or kexeced kernel).
4. After resuming from RAM/DISK, devices are put into "normal" state and
the syscall entries replaced in step 2 are restored.

Best Regards,
Huang Ying
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