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

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

[Pavel Machek]

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@ucw.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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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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

[Rafael J. Wysocki]

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@ucw.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
> 
> 
> 
> 

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

[Pavel Machek]

On Fri 2010-04-23 20:28:55, Rafael J. Wysocki wrote:
> 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).

Thanks!
								Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html