Userspace IRQ
From embeddedTS Manuals
We include a userspace IRQ patch in our 2.6 based kernels. This allows you to receive interrupts from your applications where you would normally have to write a kernel driver. This works by creating a file for each interrupt in '/proc/irq/<irqnum>/irq'. The irq file being the new addition of this patch allows you to block on a read on the file until an interrupt fires.
The original patch is documented here.