Re: hibernate/suspend-to-disk: to turn power or not?

Pavel Machek
2008-07-14T05:43:23Z

On Sun 2008-07-13 18:26:36, David Fries wrote:
> On Thu, Jan 31, 2008 at 03:40:30PM +0100, Pavel Machek wrote:
> > > Back to the original question and a proposed solution.
> > >
> > > I'm looking at the uswsusp source (while the kernel compiles),
> > > and have a question here. Is it possible to call some external
> > > application (typically a shell script) to do the final work after
> > > when the image has been written? I mean in principle - I
> > > understand there are some limitations here, but I don't know
> > > which exactly.
> >
> > No, you can't exec() anything. That would write mtime back to disk and
> > cause badness.
>
> SysRq-U remounts the disks readonly. Why not make the disks readonly
> once the kernel state is in swap, why not let any program run and give
> an error to writes?

IIRC sysrq-U does not contain all the locking that's neccessary to
make it completely safe. OTOH, it tends to work...

> I know, long dead thread, but I too would like to tell the UPS to turn
> off once the system state is resting safely in swap. Currently my
> modified apcupsd scripts tell the UPS to turn off, then tells the
> kernel to hibernate, and hopes the kernel finishes in time. I would
> much rather do things the other way, but `echo disk > /sys/power/disk`
> doesn't return until power is back on if everything goes well.

If you use s2disk, you can execute C code at the point you want...

Pavel
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