Man page 9 : parport_claim

parport_claim - claim access to a parallel port device

int parport_claim(struct pardevice *  dev );

dev
    pointer to structure representing a device on the port

This function will not block and so can be used from interrupt context. If parport_claim succeeds in claiming access to the port it returns zero and the port is available to use. It may fail (returning non-zero) if the port is in use by another driver and that driver is not willing to relinquish control of the port.