I have neither b) nor c) nowadays on powerpc.... "linux" irq numbers are
purely a virtual thing, that is an index in irq_desc array and something
we give to drivers to do request_irq() from. They can map onto hw
interrupts, MSI-like messages, environment interrupts, could be
hypervisor messgaes, in fact, it could be anything that remotely looks
like an interrupt and the concept of "hw vector" is very blurry here...
every interrupt controller defines it's own hardware vector space. On
pSeries, hardware vectors are fairly big numbers that can encode the
geographical location of the slot where the device is connected to, on
some other hypervisor, they are 64 bits "tokens" representing an
hypervisor object that can send events, etc etc....