[linux-pm] what handles disk drive(s) shutdown?

[rdunlap at xenotime.net (Randy.Dunlap)]

in Documentation/power/devices.txt, I read:

<quote>
System shutdown -- at least disks need to be spun down, or data may be
lost. Quiesce devices, just to make life easier for BIOS. event =
FREEZE, flags = SYSTEM_SHUTDOWN
</quote>

Is this actually done somewhere?  I can't find /SYSTEM_SHUTDOWN/
in any kernel .h or .c files.

Thanks,
-- 
~Randy