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

From: Pavel Machek
Date: Mon Apr 05 2010 - 02:38:43 EST


> > > 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@xxxxxx>

--- 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
The ioctl() commands recognized by the device are:

SNAPSHOT_FREEZE - freeze user space processes (the current process is

(cesky, pictures)
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