[9fans] plan9: how to get irq to mach routing

[p9 newbie]

Hi, 

I would like to retrieve what  IRQs are routed to what Machs (or lapics).  I 
dumped IOAPIC's Redirection Table entries, but  Destination bits [63:48] are 
always '0xFF'.  Is there way to determine the routing between IRQs and 
Machs/LAPICs serving them?.  One rudimentary way I tried is  that, in the 
interrupt service routine I accessed the 'm' (Mach *) external variable to 
figure the routing between the IRQ and and the Mach..  Wondering if there is a 
better way. (for all legacy, msi and msi-x interrupt types)

Thanks
rg