Name
ipc_init — 
  initialise ipc subsystem
 
Description
   
   The various sysv ipc resources (semaphores, messages and shared
   memory) are initialised.
   
   A callback routine is registered into the memory hotplug notifier
chain
   since msgmni scales to lowmem this callback routine will be
   called upon successful memory add / remove to recompute msmgni.