In the call to ddi_add_intr(9F), inumber specifies which of several possible interrupt specifications is to be handled by intr_handler. For example, if the device interrupts at only one level, pass 0 for inumber. The interrupt specifications being referred to by inumber are described by the interrupts property (see driver.conf(4), isa(4), eisa(4), mca(4), sysbus(4), vme(4), and sbus(4)). intr_handler is a pointer to a function, in this case xxintr()(), to be called when the device issues the specified interrupt. intr_handler_arg is an argument of type caddr_t to be passed to intr_handler. intr_handler_arg may be a pointer to a data structure representing the device instance that issued the interrupt. ddi_add_intr(9F) returns a device cookie in xsp->idevice_cookie for use with devices having programmable bus-interrupt levels. The device cookie contains the following fields:
u_short idev_vector; u_short idev_priority;
The idev_priority field of the returned structure contains the bus interrupt priority level, and the idev_vector field contains the vector number for vectored bus architectures such as VMEbus.
There is a potential race condition in attach(9E). The interrupt routine is eligible to be called as soon as ddi_add_intr(9F) returns. This may result in the interrupt routine being called before any mutexes have been initialized with the interrupt block cookie. If the interrupt routine acquires the mutex before it has been initialized, undefined behavior may result. See "Registering Interrupts" for a solution to this problem.