feat: add PS/2 keyboard interrupt driver by GloriousAlpaca · Pull Request #2532 · hermit-os/kernel

GloriousAlpaca · 2026-07-06T14:45:04Z

This feature adds support for the PS2 legacy keyboard in Qemu x86_64.
Currently it does:

A minimized hardware initialization (e.g. flush the output buffer) to use the keyboard, according to the standards for the Intel 8042 chip: Link to OSDev
Install an interrupt handler, which is done in the install_handlers function in interrupt.rs, as it is a hardware interrupt but does not belong in the pci interrupt handlers list (legacy device).
Add a systemcall to pop the last scancode out of the keyboard input ringbuffer (which currently has a length of 256). The Ringbuffer also uses Atomics, to prevent races and deadlocks.
The systemcall returns 0 if the keyboard feature is disabled.

I have only tested this feature with C programs on a Mac using Qemu.

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Benchmark Results

Details

Benchmark	Current: `f6c859b`	Previous: `b3883fa`	Performance Ratio
startup_benchmark Build Time	`80.43` s	`80.39` s	`1.00` ❗
startup_benchmark File Size	`0.79` MB	`0.79` MB	`1.00` ❗
Startup Time - 1 core	`0.74` s (`±0.02` s)	`0.74` s (`±0.01` s)	`0.99`
Startup Time - 2 cores	`0.75` s (`±0.02` s)	`0.75` s (`±0.02` s)	`1.00`
Startup Time - 4 cores	`0.74` s (`±0.02` s)	`0.76` s (`±0.02` s)	`0.98`
multithreaded_benchmark Build Time	`78.14` s	`83.71` s	`0.93` ❗
multithreaded_benchmark File Size	`0.90` MB	`0.90` MB	`1.00` ❗
Multithreaded Pi Efficiency - 2 Threads	`91.24` % (`±6.29` %)	`87.67` % (`±5.37` %)	`1.04`
Multithreaded Pi Efficiency - 4 Threads	`44.09` % (`±3.01` %)	`43.34` % (`±2.79` %)	`1.02`
Multithreaded Pi Efficiency - 8 Threads	`25.97` % (`±1.36` %)	`25.32` % (`±1.83` %)	`1.03`
micro_benchmarks Build Time	`77.31` s	`80.38` s	`0.96` ❗
micro_benchmarks File Size	`0.90` MB	`0.90` MB	`1.00` ❗
Scheduling time - 1 thread	`64.87` ticks (`±1.95` ticks)	`68.25` ticks (`±5.81` ticks)	`0.95`
Scheduling time - 2 threads	`35.83` ticks (`±4.52` ticks)	`38.15` ticks (`±5.34` ticks)	`0.94`
Micro - Time for syscall (getpid)	`4.31` ticks (`±0.68` ticks)	`4.13` ticks (`±0.69` ticks)	`1.05`
Memcpy speed - (built_in) block size 4096	`84909.85` MByte/s (`±58667.15` MByte/s)	`82192.20` MByte/s (`±56877.97` MByte/s)	`1.03`
Memcpy speed - (built_in) block size 1048576	`30612.01` MByte/s (`±24660.72` MByte/s)	`30409.95` MByte/s (`±24564.57` MByte/s)	`1.01`
Memcpy speed - (built_in) block size 16777216	`29334.73` MByte/s (`±24120.88` MByte/s)	`26462.68` MByte/s (`±21974.68` MByte/s)	`1.11`
Memset speed - (built_in) block size 4096	`85374.66` MByte/s (`±58982.93` MByte/s)	`82271.23` MByte/s (`±56937.12` MByte/s)	`1.04`
Memset speed - (built_in) block size 1048576	`31379.42` MByte/s (`±25114.87` MByte/s)	`31147.37` MByte/s (`±25005.00` MByte/s)	`1.01`
Memset speed - (built_in) block size 16777216	`30110.51` MByte/s (`±24574.49` MByte/s)	`27241.00` MByte/s (`±22475.91` MByte/s)	`1.11`
Memcpy speed - (rust) block size 4096	`75734.61` MByte/s (`±52842.48` MByte/s)	`74974.37` MByte/s (`±52256.45` MByte/s)	`1.01`
Memcpy speed - (rust) block size 1048576	`30314.32` MByte/s (`±24509.72` MByte/s)	`30241.00` MByte/s (`±24501.06` MByte/s)	`1.00`
Memcpy speed - (rust) block size 16777216	`29430.51` MByte/s (`±24217.05` MByte/s)	`27430.85` MByte/s (`±22631.84` MByte/s)	`1.07`
Memset speed - (rust) block size 4096	`76210.80` MByte/s (`±53189.43` MByte/s)	`75374.74` MByte/s (`±52547.87` MByte/s)	`1.01`
Memset speed - (rust) block size 1048576	`31078.99` MByte/s (`±24965.20` MByte/s)	`30996.28` MByte/s (`±24944.22` MByte/s)	`1.00`
Memset speed - (rust) block size 16777216	`30218.81` MByte/s (`±24682.21` MByte/s)	`28210.43` MByte/s (`±23118.03` MByte/s)	`1.07`
alloc_benchmarks Build Time	`76.26` s	`76.93` s	`0.99` ❗
alloc_benchmarks File Size	`0.87` MB	`0.87` MB	`1.00` ❗
Allocations - Allocation success	`91.31` %	`91.31` %	`1`
Allocations - Deallocation success	`100.00` %	`100.00` %	`1`
Allocations - Pre-fail Allocations	`61.44` %	`61.44` %	`1`
Allocations - Average Allocation time	`5077.51` Ticks (`±103.05` Ticks)	`5120.57` Ticks (`±121.11` Ticks)	`0.99`
Allocations - Average Allocation time (no fail)	`5832.75` Ticks (`±108.42` Ticks)	`5812.28` Ticks (`±133.21` Ticks)	`1.00`
Allocations - Average Deallocation time	`1294.70` Ticks (`±142.42` Ticks)	`1001.83` Ticks (`±184.72` Ticks)	`1.29` ❗
mutex_benchmark Build Time	`75.95` s	`77.85` s	`0.98` ❗
mutex_benchmark File Size	`0.90` MB	`0.90` MB	`1.00` ❗
Mutex Stress Test Average Time per Iteration - 1 Threads	`12.24` ns (`±0.68` ns)	`12.44` ns (`±0.61` ns)	`0.98`
Mutex Stress Test Average Time per Iteration - 2 Threads	`41.90` ns (`±2.26` ns)	`44.68` ns (`±3.31` ns)	`0.94`

This comment was automatically generated by workflow using github-action-benchmark.

mkroening

Thanks for the PR! :)

I was wondering why implement drivers for legacy devices instead of USB keyboards (xhci, usb-oxide, embassy-usb). I guess it is because of simplicity.

It would be great to discuss the high-level application-facing API, since that is the hardest to change once merged.

mkroening · 2026-07-07T13:22:05Z

 	"dhcpv4",
 	"fsgsbase",
 	"kernel-stack",
+    "keyboard",


I don't think this should be a default feature.

mkroening · 2026-07-07T13:28:41Z

+## Enables the PS/2 keyboard driver.
+##
+## This is only useful on PCs (x86-64).
+keyboard = []   


Could you rename this to pc-keyboard? Also, please make sure that the docs don't imply that this is needed for keyboard support in general. Serial-based keyboard support is separate from this. Similar to the framebuffer, please also put a disclaimer that this does not make the kernel use the driver and instead exposes an API for applications that need to be ported.

mkroening · 2026-07-07T13:29:25Z

+#[cfg(not(all(target_arch = "x86_64", feature = "keyboard")))]
+#[hermit_macro::system]
+#[unsafe(no_mangle)]
+pub extern "C" fn sys_read_keyboard() -> u8 {
+	0
+}


Similar to the framebuffer PR, please either merge the function definitions or (preferrably) just remove the symbol when the feature is disabled.

mkroening · 2026-07-07T13:30:39Z

 }

-pub(crate) fn install_handlers(handlers: InterruptHandlerMap) {
+pub(crate) fn install_handlers(#[allow(unused_mut)] mut handlers: InterruptHandlerMap) {


Please move the allow to the function level instead of having it inline like this.

mkroening · 2026-07-07T13:30:56Z

+pub(crate) fn install_handlers(#[allow(unused_mut)] mut handlers: InterruptHandlerMap) {
+	#[cfg(feature = "keyboard")]
+	{
+		use crate::arch::kernel::keyboard::get_keyboard_handler;


Suggested change

use crate::arch::kernel::keyboard::get_keyboard_handler;

use crate::arch::kernel::keyboard::get_keyboard_handler;

mkroening · 2026-07-07T13:45:46Z

+		data_port.write(config);
+		cmd_port.write(PS2_CMD_ENABLE_KEYBOARD);
+	}
+	fn keyboard_handler() {


Please move the handler to the top level outside of this function.

mkroening · 2026-07-07T13:47:07Z

+		while (cmd_port.read() & PS2_BUFFER_FULL) != 0 {
+			let _ = data_port.read();
+		}


Why do we discard the device buffer instead of filling our read buffer?

mkroening · 2026-07-07T13:52:13Z

+		let mut cmd_port = Port::<u8>::new(PS2_CMD_PORT);
+		let mut data_port = Port::<u8>::new(PS2_DATA_PORT);


Do you think an abstraction similar to the proposal for BGA would make sense?

struct Ps2; impl Ps2 { fn read_data() -> u8; fn write_data(data: u8); fn status() -> u8; fn command(command: u8); }

mkroening · 2026-07-07T14:02:27Z

+/// Pops a scancode from the keyboard buffer, returning None if the buffer is empty.
+pub fn pop_scancode() -> Option<u8> {


A scancode can never be zero, right? Returning Option<NonZero<u8>> would be preferable in that case.

mkroening · 2026-07-07T14:08:41Z

+#[cfg(all(target_arch = "x86_64", feature = "keyboard"))]
+#[hermit_macro::system]
+#[unsafe(no_mangle)]
+pub extern "C" fn sys_read_keyboard() -> u8 {
+	crate::kernel::keyboard::pop_scancode().unwrap_or(0)
+}


I am not too sure about this API. Is the application supposed to busy loop on this and retrieve one event at a time?

What about doing something similar to Linux's event device (evdev) interface (Linux docs)? Reading from /dev/input/event0 would then fill a user buffer with input events and blocks if no events are there unless opened with O_NONBLOCK.

mkroening self-assigned this Jul 6, 2026

GloriousAlpaca force-pushed the pr-keyboard-clean branch from 7c21b3f to 5d35a06 Compare July 6, 2026 15:33

github-actions Bot reviewed Jul 6, 2026

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GloriousAlpaca force-pushed the pr-keyboard-clean branch from 5d35a06 to 2c424d5 Compare July 6, 2026 16:07

feat: add PS/2 keyboard interrupt driver

f6c859b

GloriousAlpaca force-pushed the pr-keyboard-clean branch from 2c424d5 to f6c859b Compare July 6, 2026 16:30

mkroening requested changes Jul 7, 2026

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feat: add PS/2 keyboard interrupt driver#2532

feat: add PS/2 keyboard interrupt driver#2532
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	use crate::arch::kernel::keyboard::get_keyboard_handler;
	use crate::arch::kernel::keyboard::get_keyboard_handler;

		let mut cmd_port = Port::<u8>::new(PS2_CMD_PORT);
		let mut data_port = Port::<u8>::new(PS2_DATA_PORT);

		/// Pops a scancode from the keyboard buffer, returning None if the buffer is empty.
		pub fn pop_scancode() -> Option<u8> {

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