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

Pavel Machek
2010-04-05T06:38:52Z

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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