# NT-Lite -- an x86-64 kernel

“Not only is UNIX dead, it’s starting to smell really bad.” - Rob Pike

“UNIX has three operations: read, write, and lie through ioctl.”

## what is it?

NT-Lite is a 64-bit operating system kernel written from scratch.

It boots into a shell, loads drivers, launches programs, survives application crashes, runs Doom, plays video, talks TCP/IP, and occasionally reminds you that it is still a hobby kernel.

The codebase is small enough to understand, but no longer small enough to pretend it is just a weekend project.

## features

- UEFI bootloader
- real SMP
- physical and virtual memory managers
- kernel pool and user heap
- single address-space design with user/supervisor page permissions
- HAL split from the kernel
- preemptive priority scheduler
- processes and threads
- per-process handles with rights checks
- process exit state, reaping, and restartable init services
- events, semaphores, mutexes, queues, named queues, and alertable waits
- IRQL, DPCs, kernel APCs, and user APCs
- native user-mode exception dispatch
- Win32 vectored exception handlers
- minimal runtime-registered SEH substrate
- async file I/O with events, IOSBs, APC callbacks, and cancellation
- VFS with IRPs
- page cache with dirty writeback and invalidation
- AHCI driver, interrupt-driven
- IDE driver, PIO/DMA
- FAT32 filesystem driver with VFAT long names
- USB bus, xHCI, mass storage, and HID
- VMware SVGA display driver
- drive-number paths such as `0:/apps/shell.exe`
- PE import resolution and dynamic `.sys` driver loading
- modular networking through lwIP
- RTL8139 and RTL816x network drivers
- native BSD-ish socket syscalls
- DNS resolver syscall
- length-tracked string-view syscall ABI
- request-struct based syscalls for larger calls
- native `NTLSTATUS_*` status codes
- INI-based configuration
- partial Win32 personality
- partial (microsoft-level) POSIX personality
- Doom
- video playback
- fully GDPR-compliant
- everything but the kitchen sink

## paths

```text
"apps/shell.exe"      -> current working directory
"0:/apps/shell.exe"   -> volume 0, native path; works everywhere
"2:/data/config.ini"  -> volume 2, native path
"C:\apps\doom.exe"    -> volume 0 through win32.dll; C: maps to 0:, D: maps to 1:, etc.
"/apps/video.exe"     -> volume 0 through posix.dll
"/1/apps/video.exe"   -> volume 1 through posix.dll
```

Volumes `0`-`7` are available. A volume only works if a filesystem is registered on it.

The Win32 personality translates drive letters to volume numbers. The POSIX personality maps volumes into a tree.

## how to build

- open the VS x64 build tools as administrator
- change into this directory
- run `build.bat`
- use one of:
  - `run.bat` — IDE
  - `rund.bat` — IDE, debug
  - `runa.bat` — AHCI
  - `runad.bat` — AHCI, debug

## how it looks when built

```text
efi/boot/
  bootx64.efi
boot.ini
drivers/
  drivers.ini
  ahci.sys
  ata.sys
  fat32.sys
  lwip.sys
  pci.sys
  ps2.sys
  rtl816x.sys
  rtl8139.sys
  usb.sys
  vmwaresvga.sys
system/
  colonel.exe
  hal.dll
  init.exe
  syscall.dll
  win32.dll
  posix.dll
apps/
  shell_native.exe
  shell_win32.exe
  shell_posix.exe
  async_apc.exe
  async_cancel.exe
  doom.exe
  video.exe
  httpget.exe
  tcpserve.exe
  udp.exe
  resolve.exe
  ping.exe
```

## screenshots

![video.exe running bink video 2](image.png)

## faq

Q: Is it secure?
A: Don't connect to the internet with it.

Q: Who is this for?
A: Me.

Q: What's next?
A: todo

Q: Does it run Doom?  
A: `doom.exe`

Q: Does USB work?
A: It did for everything I threw at it.

Q: If I write a program now, will it run in the future?
A: WE DO, in fact, BREAK USERSPACE.

Q: Can you read and write files?  
A: As far as I'm aware.

Q: Does it have async I/O?  
A: The best you'll get.

Q: Does the networking actually work?
A: It didn't crash yet.

Q: Does it really have SMP?
A: Watch out. It bites.

Q: Is the Win32 layer real?  
A: Depends how you frame it. Real apps won't run but specifically prepared ones will.

Q: Are processes isolated?  
A: No. But IPC is free. Is this how a serious modern OS should isolate processes? No. 
Are we a serious OS? No. Is it very convenient? Absolutely.

Q: How often does it crash?  
A: It doesn't if you don't touch it.

Q: Can it recover from a crash?  
A: Works on my machine.

Q: Is this finished?  
A: It will be once I get a job.

Q: Will it corrupt my data?  
A: It shouldn't.

Q: Why is the path syntax so weird?  
A: It makes sense to me.

Q: Why both Win32 and POSIX?
A: NT could do it, why can't I?

Q: Why are the logs so verbose?  
A: Try debugging an interrupt path with vibes.

Q: What should I read first?  
A: This document.

Q: How do I contribute?
A: `maksw@maksw.pl`

Q: Can I use this in production?  
A: Don't.

#### Project dedicated to the honorable, esteemed Professor Leszek Wójcik through whom I came to hate Unix.