[[!meta copyright="Copyright © 2024 Free Software Foundation,
Inc."]]

[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
id="license" text="Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with no Invariant
Sections, no Front-Cover Texts, and no Back-Cover Texts.  A copy of the license
is included in the section entitled [[GNU Free Documentation
License|/fdl]]."]]"""]]

[[!tag stable_URL]]

Damien Zammit authored libirqhelp, which lets userspace attach and
handle interupts.  Suppose, a user presses a key on his keyboard, then
the keyboard can send an interrupt request (an IRQ), to the
processor.  The CPU will try to interrupt the program, so that a
callback handler can run instead.  A brief overview of `x86` interrupt
information can be found on
[[wikipedia|https://en.wikipedia.org/wiki/Interrupt_request]].  The
[[osdev wiki|https://wiki.osdev.org/IOAPIC]] has more technical
information. In `libirqhelp` the delivery of the interrupt is through an RPC
message that triggers a handler.
The source for `libirqhelp` can be found in `$hurd-src/libirqhelp/`.

First you must call `irqhelp_init ();`  Then you can install an
interrupt handler with this function:

	struct irq *
	irqhelp_install_interrupt_handler (int gsi, int bus, int dev,
	                                   int fun, void (*handler)(void*),
									   void *context);

If `gsi` is `-1`, then ACPI will look up the global system interrupt from the PCI `bus`, `dev`, and `fun`.
If `bus`, `dev`, and `fun` are `-1`, then you must define `gsi`
(global system interrupt).  You then use the returned `struct irq *`
to call the other functions.

You can enable an irq via:

	void irqhelp_enable_irq (struct irq *irq);

You can disable an irq via:

	void irqhelp_disable_irq (struct irq *irq);

You can deregister a handler via:

	error_t irqhelp_remove_interrupt_handler (struct irq *irq);

To receive irq notifications, you have to call this next function in a separate thread, giving the `struct irq *` as `arg`.

	void * irqhelp_server_loop (void *arg);