Doubt in interrupt number, how to decide device interrupted on sharing interrupt pin?

Hi,

In the following function

int request_irq( unsigned int irq,irq_handler_t handler,unsigned long irq_flags,const char * devname,void *dev_id);

how to correlate the 1st argument irq with the hardware interrupt pins. ie ) how to decide the interrupt number we have to use for a specific interrupt pin?

And while sharing the interrupt pins how to decide which device interrupted and process the correct interrupt handler as the Programmable Interrupt Controller status register value will be same for all the devices interrupted as it shares the same pin? Can I get any hardware specific examples?

Please help!

"Linux Device Drivers", O'Reilley, has an entire chapter on writing interrupt handlers.