linux-kernel - document open(/dev/snapshot) sideeffects -- was Re: [linux-pm] syncing the disks when entering sleep

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Date:	Mon, 5 Apr 2010 08:38:52 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	"Leisner, Martin" <Martin.Leisner@...ox.com>,
	linux-pm@...ts.linux-foundation.org, Andrew Morton <akpm@...l.org>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: document open(/dev/snapshot) sideeffects -- was Re: [linux-pm]
 syncing the disks when entering sleep

Hi!

> > > Please note that merely _opening_ /dev/snapshot has side effects, so that's
> > > not just "three ioctls".
> > 
> > I search Doc*/power/userland-swsusp.txt, and could not find mentions
> > of sideeffects. Perhaps that should be fixed?
> 
> Please feel free to make the docs more complete, then.

Yes, something like this?

Signed-off-by: Pavel Machek <pavel@....cz>

--- a/Documentation/power/userland-swsusp.txt
+++ b/Documentation/power/userland-swsusp.txt
@@ -24,6 +24,10 @@ assumed to be in the resume mode.  The device cannot be open for simultaneous
 reading and writing.  It is also impossible to have the device open more than
 once at a time.
 
+Even opening the device has side effects. Data structures are
+allocated, and PM_HIBERNATION_PREPARE / PM_RESTORE_PREPARE chains are
+called.
+
 The ioctl() commands recognized by the device are:
 
 SNAPSHOT_FREEZE - freeze user space processes (the current process is



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