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

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Date:	Fri, 23 Apr 2010 20:28:55 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
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: Re: document open(/dev/snapshot) sideeffects -- was Re: [linux-pm] syncing the disks when entering sleep

On Monday 05 April 2010, Pavel Machek wrote:
> 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?

Yes, looks reasonable.

I've applied it to suspend-2.6/linux-next (added a changelog).

Rafael


> 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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