--------------------------------------------------------------------------------
xv6-vfs is an "enhanced" version of xv6 with Virtual Filesystem Support (VFS)
rather than the original filesystem layers approach. This was implemented as my
final project for CS 3210 -- Operating Systems @ Georgia Tech.

The original filesystem code (fs.c and fs.h) has been completely removed and is
replaced with VFS code (vfs.c and vfs.h) as well as SFS code (sfs.c), which is
a custom, simplified Unix filesystem.

The IDE support code (ide.c) was revamped to support disks with multiple
partitions using the Master Boot Record (MBR) format. The detected partitions
are registered on-boot with the VFS subsystem.

The block cache (bio.c) code was removed completely. All blocks are read from
and written to the disk directly -- there currently is NO caching mechanism in
place. For the scope of this project, that is okay, but performance will not be
very good.

The logging (log.c) code was also removed. Once again, for the scope and
purposes of this project, that is okay. However, for fault-tolerance purposes,
journaling support is crucial.
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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/6.828/2016/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, and Austin
Clements.

We are also grateful for the bug reports and patches contributed by Silas
Boyd-Wickizer, Anton Burtsev, Cody Cutler, Mike CAT, Tej Chajed, Nelson Elhage,
Saar Ettinger, Alice Ferrazzi, Nathaniel Filardo, Peter Froehlich, Yakir Goaron,
Shivam Handa, Bryan Henry, Jim Huang, Alexander Kapshuk, Anders Kaseorg,
kehao95, Wolfgang Keller, Eddie Kohler, Austin Liew, Imbar Marinescu, Yandong
Mao, Hitoshi Mitake, Carmi Merimovich, Joel Nider, Greg Price, Ayan Shafqat,
Eldar Sehayek, Yongming Shen, Cam Tenny, Rafael Ubal, Warren Toomey, Stephen Tu,
Pablo Ventura, Xi Wang, Keiichi Watanabe, Nicolas Wolovick, Grant Wu, Jindong
Zhang, Icenowy Zheng, and Zou Chang Wei.

The code in the files that constitute xv6 is
Copyright 2006-2016 Frans Kaashoek, Robert Morris, and Russ Cox.

ERROR REPORTS

Please send errors and suggestions to Frans Kaashoek and Robert Morris
(kaashoek,rtm@mit.edu). The main purpose of xv6 is as a teaching
operating system for MIT's 6.828, so we are more interested in
simplifications and clarifications than new features.

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/6.828/2016/tools.html.
Then run "make TOOLPREFIX=i386-jos-elf-". Now install the QEMU PC
simulator and run "make qemu".