s2both

[David Zeuthen]

On Sun, 2007-03-11 at 01:13 +0100, Tim Dijkstra wrote:
> Hi,
> 
> Both suspend.sf.net and suspend2 have a notion of s2both. That is,
> before suspending to ram, the state of the system is saved to disk just
> like would happen for hibernate.
> This has the obvious benefit of being able to resume in case you
> deplete your batteries while you laptop is suspended.
> 
> I think it would really be useful to have the possibility to do that
> instead of plain s2ram when one suspends. We can of course just make
> use of the possibility in pm-utils when it is available, but I guess a
> checkbox in g-p-m would be nice. For that to work we also need another
> attribute in hal.
> 
> Comments?

This is really just a third sleep mechanism so what I think we need is

 - a new method on HAL called SuspendHybrid() - this is on the same
   interface as Suspend() and Hibernate()

 - a new property on HAL called

     power_management.can_suspend_hybrid

   to go with .can_suspend and .can_hibernate

Now, there's a bug in HAL already in how we compute the .can_suspend
and .can_hibernate values. For example, here on Fedora, HAL says that my
system can hibernate just fine but that's a LIE since at least on Fedora
this doesn't work when using a swap file instead of a swap partition. I
think this works on other distros though.

Anyway, since pm-utils is the mechanism for HAL, we want to pm-utils to
report all this HAL. FWIW, this is even more needed when we want to do
things like hybrid suspends. But unless someone actually makes a
pm-utils release _this week_ with such a tool for reporting what the
machine can do [1] I'm afraid this can't go into HAL 0.5.9. That means
it would be good to start writing patches for both HAL and pm-utils and
getting them past these maintainers. 

Peter, is this something you can look at / comment on? (Btw, we _need_ a
pm-utils upstream release this week.)

As to presenting these options in the UI, I'll add my two cents and say
it's a useless option to present to the casual user - just always use
hybrid sleep if available (am not terribly interested in discussing the
UI on these lists either - I think the g-p-m and kpowersave guys can
figure this out themselves).

      David


[1] : it could be called pm-is-supported and would be called by HAL like
this

 pm-is-supported --suspend
 pm-is-supported --suspend-hybrid
 pm-is-supported --hibernate