[systemd-devel] System power control

[David Lambert]

I am developing a battery backed up cape for a Beaglebone project which 
uses systemd under Angstrom. In order to conserve battery life, I would 
like to signal my battery control hardware via a GPIO when system 
shutdown is complete and all file systems have been dismounted. Is there 
a "hook" in systemd which will allow me to call a small user helper 
program at this point. Looking at the shutdown.c source, I see the 
following code:

         if (access("/run/initramfs/shutdown", X_OK) == 0) {

                 if (prepare_new_root() >= 0 &&
                     pivot_to_new_root() >= 0) {
                         execv("/shutdown", argv);
                         log_error("Failed to execute shutdown binary: %m");
                 }
         }

Is the intention of this code to provide such a hook? Can I cheat by 
creating /run/initramfs/ just prior to shutdown and copy a small 
shutdown executable of my own here. This sounds like it may work, but 
seems like a terrible hack. I feel that there should be a more elegant 
way to achieve this goal.

Thanks for any advice.

Dave.