Enrico Fraccaroli
329 lines
9.1 KiB
Markdown
329 lines
9.1 KiB
Markdown
# MentOS
|
|
|
|
[](https://forthebadge.com)
|
|
[](https://forthebadge.com)
|
|
[](https://forthebadge.com)
|
|
|
|
## 1. What is MentOS
|
|
|
|
MentOS (Mentoring Operating System) is an open source educational operating
|
|
system. The goal of MentOS is to provide a project environment that is realistic
|
|
enough to show how a real Operating System work, yet simple enough that students
|
|
can understand and modify it in significant ways.
|
|
|
|
There are so many operating systems, why did we write MentOS? It is true, there
|
|
are a lot of education operating system, BUT how many of them follow the
|
|
guideline de fined by Linux?
|
|
|
|
MentOS aims to have the same Linux's data structures and algorithms. It has a
|
|
well-documented source code, and you can compile it on your laptop in a few
|
|
seconds!
|
|
|
|
If you are a beginner in Operating-System developing, perhaps MentOS is the
|
|
right operating system to start with.
|
|
|
|
Parts of MentOS are inherited or inspired by a similar educational operating
|
|
system called [DreamOs](https://github.com/dreamos82/DreamOs) written by Ivan
|
|
Gualandri.
|
|
|
|
## 2. Implemented features
|
|
Follows the list of implemented features:
|
|
|
|
**Processes and Events**
|
|
- [x] Memory protection (User vs Kernel);
|
|
- [x] Processes;
|
|
- [x] Scheduler (synchronous and asynchronous);
|
|
- [x] Interrupts and Exceptions;
|
|
- [x] Signals;
|
|
- [x] Timers and RTC;
|
|
- [x] Wait-queues;
|
|
- [x] System Calls;
|
|
- [ ] Multi-core;
|
|
|
|
**Memory**
|
|
- [x] Paging;
|
|
- [x] Buddy System;
|
|
- [x] Slab Allocation;
|
|
- [x] Zone Allocator;
|
|
- [x] Cache Allocator;
|
|
- [x] Heap;
|
|
- [x] Virtual Addressing;
|
|
|
|
**Filesystem**
|
|
- [x] Virtual Filesystem (VFS);
|
|
- [x] Initramfs;
|
|
- [x] EXT2;
|
|
- [x] Procfs;
|
|
|
|
**Input/Output**
|
|
- [x] Programmable Interrupt Controller (PIC) drivers;
|
|
- [x] Keyboard drivers (IT/ENG layouts);
|
|
- [x] Video drivers;
|
|
- [ ] VGA drivers;
|
|
|
|
I will try to keep it updated...
|
|
|
|
## 3. Prerequisites
|
|
|
|
MentOS is compatible with the main **unix-based** operating systems. It has been
|
|
tested with *Ubuntu*, *WSL1*, *WSL2*, and *MacOS*.
|
|
|
|
### 3.1. Generic Prerequisites
|
|
|
|
#### 3.1.1. Compile
|
|
|
|
For compiling the system:
|
|
|
|
- nasm
|
|
- gcc
|
|
- make
|
|
- cmake
|
|
- git
|
|
- ccmake (suggested)
|
|
- e2fsprogs (should be already installed)
|
|
|
|
Under **MacOS**, for compiling, you have additional dependencies:
|
|
|
|
- i386-elf-binutils
|
|
- i386-elf-gcc
|
|
|
|
#### 3.1.2. Execute
|
|
|
|
To execute the operating system, you need to install:
|
|
|
|
- qemu-system-i386 (or qemu-system-x86)
|
|
|
|
#### 3.1.3. Debug
|
|
|
|
For debugging we suggest using:
|
|
|
|
- gdb or cgdb
|
|
|
|
### 3.2. installation Prerequisites
|
|
|
|
Under **Ubuntu**, you can type the following commands:
|
|
|
|
```bash
|
|
sudo apt-get update && sudo apt-get upgrade -y
|
|
sudo apt-get install -y build-essential git cmake qemu-system-x86 nasm e2fsprogs
|
|
sudo apt-get install -y gdb cgdb
|
|
```
|
|
Note: Older versions might have `qemu-system-i386` instead of `qemu-system-x86`.
|
|
|
|
Under **MacOS** you also need to install the i386-elf cross-compiler. The
|
|
simplest installation method is through Homebrew package manager.
|
|
Install [Homebrew](https://brew.sh/index_it) if you don't already have it, and
|
|
then type the following commands:
|
|
|
|
```bash
|
|
brew update && brew upgrade
|
|
brew install i386-elf-binutils i386-elf-gcc git cmake qemu nasm e2fsprogs
|
|
brew install gdb cgdb #<- for debug only
|
|
```
|
|
|
|
## 4. Compiling MentOS and generating the EXT2 filesystem
|
|
|
|
Compile MentOS with:
|
|
|
|
```bash
|
|
cd <clone_directory>
|
|
mkdir build
|
|
cd build
|
|
cmake ..
|
|
make
|
|
```
|
|
|
|
Then, generate the EXT2 filesystem with:
|
|
|
|
```bash
|
|
make filesystem
|
|
```
|
|
you just need to generate the filesystem once. If you change a `program` you need to re-generate the entire filesystem with `make filesystem`, but this will override any changes you made to the files inside the `rootfs.img`. In the future I will find a way to update just the `/usr/bin` directory and the programs.
|
|
|
|
## 5. Running MentOS
|
|
|
|
Boot MentOS with qemu:
|
|
|
|
```bash
|
|
make qemu
|
|
```
|
|
|
|
To login, use one of the usernames listed in `files/etc/passwd`.
|
|
|
|
## 6. Kernel logging
|
|
The kernel provides ways of printing logging messages *from* inside the kernel code *to* the bash where you executed the `make qemu`.
|
|
|
|
These *logging* functions are:
|
|
```C++
|
|
#define pr_emerg(...)
|
|
#define pr_alert(...)
|
|
#define pr_crit(...)
|
|
#define pr_err(...)
|
|
#define pr_warning(...)
|
|
#define pr_notice(...)
|
|
#define pr_info(...)
|
|
#define pr_debug(...)
|
|
#define pr_default(...)
|
|
```
|
|
|
|
You use them like you would use a `printf`:
|
|
```C++
|
|
if (fd < 0) {
|
|
pr_err("Failed to open file '%s', received file descriptor %d.\n", filename, fd);
|
|
return 1;
|
|
}
|
|
```
|
|
|
|
By default only message that goes from `pr_notice` included down to `pr_emerg` are displayed.
|
|
|
|
Each logging function (they are actually macros) is a wrapper that automatically sets the desired **log level**. Each log level is identified by a number, and declared as follows:
|
|
```C++
|
|
#define LOGLEVEL_DEFAULT (-1) ///< default-level messages.
|
|
#define LOGLEVEL_EMERG 0 ///< system is unusable.
|
|
#define LOGLEVEL_ALERT 1 ///< action must be taken immediately.
|
|
#define LOGLEVEL_CRIT 2 ///< critical conditions.
|
|
#define LOGLEVEL_ERR 3 ///< error conditions.
|
|
#define LOGLEVEL_WARNING 4 ///< warning conditions.
|
|
#define LOGLEVEL_NOTICE 5 ///< normal but significant condition.
|
|
#define LOGLEVEL_INFO 6 ///< informational.
|
|
#define LOGLEVEL_DEBUG 7 ///< debug-level messages.
|
|
```
|
|
|
|
You can change the logging level by including the following lines at the beginning of your source code:
|
|
```C++
|
|
// Include the kernel log levels.
|
|
#include "sys/kernel_levels.h"
|
|
/// Change the header.
|
|
#define __DEBUG_HEADER__ "[ATA ]"
|
|
/// Set the log level.
|
|
#define __DEBUG_LEVEL__ LOGLEVEL_INFO
|
|
```
|
|
This example sets the `__DEBUG_LEVEL__`, so that all the messages from `INFO` and below are shown. While `__DEBUG_HEADER__` is just a string that is automatically prepended to your message, helping you identifying from which code the message is coming from.
|
|
|
|
## 7. Change the scheduling algorithm
|
|
|
|
MentOS provides three different scheduling algorithms:
|
|
|
|
- Round-Robin
|
|
- Priority
|
|
- Completely Fair Scheduling
|
|
|
|
If you want to change the scheduling algorithm:
|
|
|
|
```bash
|
|
|
|
cd build
|
|
|
|
# Round Robin scheduling algorithm
|
|
cmake -DSCHEDULER_TYPE=SCHEDULER_RR ..
|
|
# Priority scheduling algorithm
|
|
cmake -DSCHEDULER_TYPE=SCHEDULER_PRIORITY ..
|
|
# Completely Fair Scheduling algorithm
|
|
cmake -DSCHEDULER_TYPE=SCHEDULER_CFS ..
|
|
|
|
make
|
|
make qemu
|
|
```
|
|
|
|
Otherwise you can use `ccmake`:
|
|
|
|
```bash
|
|
cd build
|
|
cmake ..
|
|
ccmake ..
|
|
```
|
|
|
|
Now you should see something like this:
|
|
|
|
```
|
|
BUILD_DOCUMENTATION ON
|
|
CMAKE_BUILD_TYPE
|
|
CMAKE_INSTALL_PREFIX /usr/local
|
|
DEBUGGING_TYPE DEBUG_STDIO
|
|
ENABLE_BUDDY_SYSTEM OFF
|
|
SCHEDULER_TYPE SCHEDULER_RR
|
|
```
|
|
|
|
Select SCHEDULER_TYPE, and type Enter to scroll the three available algorithms
|
|
(SCHEDULER_RR, SCHEDULER_PRIORITY, SCHEDULER_CFS). Afterwards,
|
|
|
|
```bash
|
|
<press c>
|
|
<press g>
|
|
make
|
|
make qemu
|
|
```
|
|
|
|
## 8. Use Debugger
|
|
|
|
If you want to use GDB to debug MentOS, first you need to compile everything:
|
|
|
|
```bash
|
|
cd build
|
|
cmake ..
|
|
make
|
|
```
|
|
|
|
Then, you need to generate a file called `.gdbinit` placed inside the `build` directory, which will tell **gdb** which *object* file he needs to read in order to allow proper debugging.
|
|
```bash
|
|
make gdb_file
|
|
```
|
|
|
|
Finally, you run qemu in debugging mode with:
|
|
```bash
|
|
make qemu-gdb
|
|
```
|
|
If you did everything correctly, you should see an empty QEMU window. Basically, QEMU is waiting for you to connect *remotely* with gdb. Anyway, running `make qemu-gdb` will make your current shell busy, you cannot call `gdb` in it. You need to open a new shell inside the `build` folder and do a:
|
|
```bash
|
|
cgdb -q -iex 'add-auto-load-safe-path .'
|
|
```
|
|
|
|
Now you will have:
|
|
1. the QEMU window waiting for you,
|
|
2. the shell where you ran `make qemu-gdb` also waiting for you,
|
|
3. the debugger that loaded a series of symbol files and the location of their `.text` section.
|
|
|
|
By default I placed a breakpoint at the begginning of 1) the bootloader, 2) the `kmain` function of the kernel.
|
|
|
|
So, when gdb starts you need to first give a continue:
|
|
```bash
|
|
(gdb) continue
|
|
```
|
|
|
|
This will make the kernel run, and stop at the first breakpoint which is inside the *bootloader*:
|
|
```bash
|
|
Breakpoint 1, boot_main (...) at .../mentos/src/boot.c:220
|
|
220 {
|
|
```
|
|
|
|
giving a second `continue` will get you to the start of the operating system:
|
|
|
|
This will make the kernel run, and stop at the first breakpoint which is inside the *bootloader*:
|
|
```bash
|
|
Breakpoint 2, kmain (...) at .../mentos/src/kernel.c:95
|
|
95 {
|
|
```
|
|
|
|
## 9. Contributors
|
|
|
|
Project Manager:
|
|
|
|
* [Enrico Fraccaroli](https://github.com/Galfurian)
|
|
|
|
Developers:
|
|
* [Alessandro Danese](https://github.com/alessandroDanese88), [Luigi Capogrosso](https://github.com/luigicapogrosso), [Mirco De Marchi](https://github.com/mircodemarchi)
|
|
- Protection ring
|
|
- libc
|
|
* Andrea Cracco
|
|
- Buddy System, Heap, Paging, Slab, Caching, Zone
|
|
- Process Image, ELF
|
|
- VFS: procfs
|
|
- Bootloader
|
|
* Linda Sacchetto, Marco Berti
|
|
- Real time scheduler
|
|
* Daniele Nicoletti, Filippo Ziche
|
|
- Real time scheduler (Asynchronous EDF)
|
|
- Soft IRQs
|
|
- Timer
|
|
- Signals
|