minios

A very simple operating system for i386 with its own bootloader, just for self learning. So far these features are implemented:

• bootloader with available memory detection.
• Basic chipset and buses: PCI, PIC, PIT, Serial, PS/2 in progress.
• Text console and QEMU-compatible graphics mode.
• Keyboard and mouse drivers.
• base libraries: strings, heap, string/int conversion, etc.
• IDE harddisk (read only, no IRQ, no DMA).
• Virtual file system layer.
• ext2 filesystem (readonly so far).
• Elf binary support - no shared libraries.
• Paging.
• Context switching.
• Basic IPC by using message passing.
• Process loading and execution.
• Loadable kernel modules, used for device drivers.
• Minimal userspace C library.
• Minimal command line interface.
• System calls for:
  • Open/close/read files, directories and stream handling.
  • Exit current process.
  • Yield process.
  • Spawn processes.
  • Wait for process finalization.
  • Messge passing.

Requirements

• gcc
• nasm
• qemu

Build

Run make

Test

Run make test

Debug

Run make debug From another console, you can connect with gdb at port 1234 of localhost.

Debug messages

Port 0x08 (COM1) of guest is used for debugging purposes, it is sent to host console (on test target), or to file minios.log (on debug target).

Using

So far the very first thing the kernel executes on user space is a shell interface.

Shell

The shell supports a very limited set of features. It works pretty much like a regular unix/DOS shell. The following builtin commants are included

• clear: clear screen
• pwd: shows current directory
• env: shows environment variables
• cd: changes directory (not working yet). Any other input will be handled as program name. For the moment it executes all programs which are on PATH environment variable (only one single location supported so far). The default working directory is disk0:/ Executables have .elf extension, although is not needed to write it. Appending & at the end of the command will cause the executed problem be run in background.

ls

Shows a given directory. Syntax: $ ls [path] Path can be relative, absolute with no drive, or absolute with drive included.

lsdev

Lists all available devices

cat

Dumps to console the contents of a given file, syntax: $ cat [path]

free

Displays user and kernel memory statistics.

ps

Shows current processes

Filesystem and devices.

There isn't a signle file system as in unix, instead devices can have a filesystem associated. Devices are identified by its type and instance number, in this way:

• disk0: The main drive
• sys0: A virtual device which is a place holder where system fs is mounted on.
• keyboard0: raw keyboard access.
• screen0: Raw screen access.
• console0: This is a "device" which ends up using keyboard and screen, if present, processes reference it for stdin, stdout, and stderr.
• net0: Raw ethernet access, supported by rtl8139 driver.

Finally, the filesystems available for the moment are these:

• disk0:/ the main ext2 filesystem
• sys0:/ this file system provides access to system resources, like processes, memory statistics, and IPC resources (in progress). Programs like ps and free read this filesystem to show system information.