Versions of Linux beginning with 2.1.30 don’t define the functions queue_task_irq and queue_task_irq_off, as the actual speed-up over queue_task was not worth the effort of maintaining two separate functions. This became evident while new mechanisms were being added to the kernel.

At the source level, this is the only difference between 2.1 and 2.0; the header sysdep-2.1.h defines the missing functions to ease porting drivers from 2.0. The curious reader is urged to look in <asm/spinlock.h> for more details.