detecting hibernation capability

[Ben Liblit]

Is there a standard way for HAL to report whether a machine is capable 
of hibernating?  If not, should there be?  Is this the sort of thing HAL 
ought to own?

I dearly hope that my laptop will be able to hibernate one day, but it 
certainly cannot now.  I'm not using swsusp2 or similar things, and 
directly running "echo disk > /sys/power/state" yields EINVAL.

Detecting that my laptop cannot hibernate ought to be easy; "cat 
/sys/power/state" reports "standby mem" with no mention of "disk". 
Perhaps there will be weird corner cases or exceptions, but one hopes 
that checking this file will be the right thing in the majority of cases.

Centralized detection of hibernation capability may be of interest to 
many power-related applications.  It is certainly of interest to 
gnome-power-manager, which currently simply assumes that hibernation is 
available.  If it is not available, then several hibernation-related GUI 
elements ought to be disabled accordingly.