Apologies for cross-posting this to two lists.  I am the FreeBSD ACPI 
maintainer and recently someone brought to my attention that the X 
server expects notification/control over the suspend/resume process. 
This event is implemented in this file:

xc/programs/Xserver/hw/xfree86/os-support/bsd/bsd_apm.c

This interface works for apm (except that it only has NetBSD defines 
currently) but is not implemented for ACPI.  I'd like more information 
as to what the X server actually does with this event.  Is there any 
situation where it actually needs to veto a suspend?  Does it 
potentially take seconds to save state?  Does it need to access other 
running subsystems or is it self-contained?

I've started by adding some compat defines for FreeBSD, in the attached 
patch.  Please let me know more about the expected semantics of this 
event and any caveats.

Thanks,
Nate