This project contains all my modifications made to xv6 as part of my operating systems class at Portland State University during the Summer 2018 term. xv6 was modified over 5 sub-projects that expanded features and functionality. These are:
Project 1: Learning flow of control in xv6, implementing system calls and accessing process-specific information.
Project 2: Adding groups and users for processes, timing process CPU usage and user-level commands for process information.
Project 3: Improving process management and efficiency using linked lists (scheduling went from O(n) -> O(1)), expanded console debugging with new control commands.
Project 4: Optimizing process scheduling algorithm using multi-level feedback queues to promote process fairness.
Project 5: Implementing file protections via permissions.
NOTE: All the changes I made are wrapped in #CS333_P1, #CS333_P2 etc preprocessor directives where the number after P defines the project. This allowed for project-by-project changes to be easily understood, as well as simplifying debugging. Most changes were made to the following files:
-proc.h
-proc.c
-sysproc.c
-syscall.c
-exec.c
xv6 is a re-implementation of Dennis Ritchie's and Ken Thompson's Unix Version 6 (v6). xv6 loosely follows the structure and style of v6, but is implemented for a modern x86-based multiprocessor using ANSI C.
ACKNOWLEDGMENTS
xv6 is inspired by John Lions's Commentary on UNIX 6th Edition (Peer to Peer Communications; ISBN: 1-57398-013-7; 1st edition (June 14, 2000)). See also http://pdos.csail.mit.edu/6.828/2014/xv6.html, which provides pointers to on-line resources for v6.
xv6 borrows code from the following sources: JOS (asm.h, elf.h, mmu.h, bootasm.S, ide.c, console.c, and others) Plan 9 (entryother.S, mp.h, mp.c, lapic.c) FreeBSD (ioapic.c) NetBSD (console.c)
The following people have made contributions: Russ Cox (context switching, locking) Cliff Frey (MP) Xiao Yu (MP) Nickolai Zeldovich Austin Clements
In addition, we are grateful for the bug reports and patches contributed by Silas Boyd-Wickizer, Peter Froehlich, Shivam Handa, Anders Kaseorg, Eddie Kohler, Yandong Mao, Hitoshi Mitake, Carmi Merimovich, Joel Nider, Greg Price, Eldar Sehayek, Yongming Shen, Stephen Tu, and Zouchangwei.
The code in the files that constitute xv6 is Copyright 2006-2014 Frans Kaashoek, Robert Morris, and Russ Cox.
ERROR REPORTS
If you spot errors or have suggestions for improvement, please send email to Frans Kaashoek and Robert Morris (kaashoek,rtm@csail.mit.edu).
BUILDING AND RUNNING XV6
To build xv6 on an x86 ELF machine (like Linux or FreeBSD), run "make". On non-x86 or non-ELF machines (like OS X, even on x86), you will need to install a cross-compiler gcc suite capable of producing x86 ELF binaries. See http://pdos.csail.mit.edu/6.828/2014/tools.html. Then run "make TOOLPREFIX=i386-jos-elf-".
To run xv6, install the QEMU PC simulators. To run in QEMU, run "make qemu".
To create a typeset version of the code, run "make xv6.pdf". This requires the "mpage" utility. See http://www.mesa.nl/pub/mpage/.