Keean Schupke wrote:
Look at how Linux scans the hardware at boot time and initialises a driver for each device it finds... that means that each driver is parameterised by the IO address of the device, and can be initialised multiple times. When an OS boots it runs an initialisation routine (the 'main' of the kernel) This is just like the main in a Haskell program - there is no need for anything to be initialised _before_ main runs... The init routine calls init on each device driver in turn, finally handing control over to the scheduler, which loads the 'init' program and that starts all the user programs. I don't see any calls for unique guarantees here...
Hear, hear! :) And to continue on the issue of device IO. If you look at real, portable operating systems, the drivers are actually parametrized on the methods to do IO to the device. The reason is that different busses require different ways to do IO (accessing a chip on ISA bus is not the same as when the chip sits in a USB device). But you want to reuse the same driver regardless of the bus, you drivers have to take the device access methods as arguments. In all the device drivers I've written there has never been anything in any driver that makes sure you don't initialize it twice. On the contrary. You need to initialize it once for each device. It's the bus driver that makes sure you get one driver per device. And the driver on top of the bus driver makes sure you get one bus driver per bus, etc. (At the very top there's only one instance (per machine), "mainbus". Creating one copy of this would be the responsibility of main in a Haskell OS.) -- Lennart