xv6: refresh from 2010 page
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Russ Cox
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index.html: index.txt mkhtml
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./mkhtml index.txt >_$@ && mv _$@ $@
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BIN
web/boot.pdf
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web/disk.pdf
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web/exec.pdf
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web/exec.pdf
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web/fscall.pdf
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web/fscall.pdf
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web/fsdata.pdf
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<!-- AUTOMATICALLY GENERATED: EDIT the .txt version, not the .html version -->
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<html>
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<html>
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<head>
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<head>
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<title>Xv6, a simple Unix-like teaching operating system</title>
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<title>Xv6, a simple Unix-like teaching operating system</title>
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@ -32,31 +31,36 @@ h2 {
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--></style>
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--></style>
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</head>
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</head>
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<body bgcolor=#ffffff>
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<body bgcolor=#ffffff>
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<h1>Xv6, a simple Unix-like teaching operating system</h1>
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<h1>Xv6, a simple Unix-like teaching operating system</h1>
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<br><br>
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Xv6 is a teaching operating system developed
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<h2>Introduction</h2>
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in the summer of 2006 for MIT's operating systems course,
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“6.828: Operating Systems Engineering.”
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Xv6 is a teaching operating system developed in the summer of 2006 for
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We used it for 6.828 in Fall 2006 and Fall 2007
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MIT's operating systems
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and are using it this semester (Fall 2008).
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course, <a href="http://pdos.csail.mit.edu/6.828">6.828: operating
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We hope that xv6 will be useful in other courses too.
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systems Engineering</a>. We hope that xv6 will be useful in other
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This page collects resources to aid the use of xv6
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courses too. This page collects resources to aid the use of xv6 in
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in other courses.
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other courses, including a commentary on the source code itself.
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<p><font color="red">Status: The xv6 code is in pretty good shape, but
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the commentary is rough.</font>
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<h2>History and Background</h2>
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<h2>History and Background</h2>
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For many years, MIT had no operating systems course.
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In the fall of 2002, Frans Kaashoek, Josh Cates, and Emil Sit
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<p>For many years, MIT had no operating systems course. In the fall
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created a new, experimental course (6.097)
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of 2002, Frans Kaashoek, Josh Cates, and Emil Sit created a new,
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to teach operating systems engineering.
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experimental course (6.097) to teach operating systems engineering.
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In the course lectures, the class worked through Sixth Edition Unix (aka V6)
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In the course lectures, the class worked through <a href="#v6">Sixth
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using John Lions's famous commentary.
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Edition Unix (aka V6)</a> using John Lions's famous commentary. In
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In the lab assignments, students wrote most of an exokernel operating
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the lab assignments, students wrote most of an exokernel operating
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system, eventually named Jos, for the Intel x86.
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system, eventually named Jos, for the Intel x86. Exposing students to
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Exposing students to multiple systems–V6 and Jos–helped
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multiple systems–V6 and Jos–helped develop a sense of the
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develop a sense of the spectrum of operating system designs.
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spectrum of operating system designs. In the fall of 2003, the
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In the fall of 2003, the experimental 6.097 became the
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experimental 6.097 became the official course 6.828; the course has
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official course 6.828; the course has been offered each fall since then.
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been offered each fall since then.
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<br><br>
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<p>
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V6 presented pedagogic challenges from the start.
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V6 presented pedagogic challenges from the start.
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Students doubted the relevance of an obsolete 30-year-old operating system
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Students doubted the relevance of an obsolete 30-year-old operating system
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written in an obsolete programming language (pre-K&R C)
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written in an obsolete programming language (pre-K&R C)
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@ -76,13 +80,12 @@ uniprocessors such as
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enabling/disabling interrupts) and helps relevance.
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enabling/disabling interrupts) and helps relevance.
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Finally, writing a new system allowed us to write cleaner versions
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Finally, writing a new system allowed us to write cleaner versions
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of the rougher parts of V6, like the scheduler and file system.
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of the rougher parts of V6, like the scheduler and file system.
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<br><br>
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<p> 6.828 substituted xv6 for V6 in the fall of 2006. Based on
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6.828 substituted xv6 for V6 in the fall of 2006.
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that experience, we cleaned up rough patches of xv6. Since then, xv6
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Based on that experience, we cleaned up rough patches
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has stabilized, so we are making it available in the hopes that others
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of xv6 for the course in the fall of 2007.
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will find it useful too.
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Since then, xv6 has stabilized, so we are making it
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available in the hopes that others will find it useful too.
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<p>
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<br><br>
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6.828 uses both xv6 and Jos.
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6.828 uses both xv6 and Jos.
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Courses taught at UCLA, NYU, Peking University, Stanford, Tsinghua,
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Courses taught at UCLA, NYU, Peking University, Stanford, Tsinghua,
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and University Texas (Austin) have used
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and University Texas (Austin) have used
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@ -90,14 +93,16 @@ Jos without xv6; we believe other courses could use
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xv6 without Jos, though we are not aware of any that have.
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xv6 without Jos, though we are not aware of any that have.
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<h2>Xv6 sources</h2>
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<h2>Xv6 sources</h2>
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The latest xv6 is <a href="xv6-rev4.tar.gz">xv6-rev4.tar.gz</a>.
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The latest xv6 is <a href="../src/xv6-rev4.tar.gz">xv6-rev4.tar.gz</a>.
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We distribute the sources in electronic form but also as
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We distribute the sources in electronic form but also as
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a printed booklet with line numbers that keep everyone
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a printed booklet with line numbers that keep everyone
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together during lectures. The booklet is available as
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together during lectures. The booklet is available as
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<a href="xv6-rev4.pdf">xv6-rev4.pdf</a>.
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<a href="../src/xv6-rev4.pdf">xv6-rev4.pdf</a>.
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The xv6 source code is licensed under the traditional <a href="http://www.opensource.org/licenses/mit-license.php">MIT license</a>;
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The xv6 source code is licensed under the traditional <a href="http://www.opensource.org/licenses/mit-license.php">MIT license</a>;
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see the LICENSE file in the source distribution.
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see the LICENSE file in the source distribution.
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<br><br>
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<p>
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xv6 compiles using the GNU C compiler,
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xv6 compiles using the GNU C compiler,
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targeted at the x86 using ELF binaries.
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targeted at the x86 using ELF binaries.
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On BSD and Linux systems, you can use the native compilers;
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On BSD and Linux systems, you can use the native compilers;
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@ -106,239 +111,131 @@ you must use a cross-compiler.
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Xv6 does boot on real hardware, but typically
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Xv6 does boot on real hardware, but typically
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we run it using the Bochs emulator.
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we run it using the Bochs emulator.
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Both the GCC cross compiler and Bochs
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Both the GCC cross compiler and Bochs
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can be found on the <a href="../../2007/tools.html">6.828 tools page</a>.
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can be found on the <a href="../2010/tools.html">6.828 tools page</a>.
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<h2>Lectures</h2>
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<h2>Xv6 lecture material</h2>
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In 6.828, the lectures in the first half of the course
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introduce the PC hardware, the Intel x86, and then xv6.
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The lectures in the second half consider advanced topics
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using research papers; for some, xv6 serves as a useful
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base for making discussions concrete.
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This section describe a typical 6.828 lecture schedule,
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linking to lecture notes and homework.
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A course using only xv6 (not Jos) will need to adapt
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a few of the lectures, but we hope these are a useful
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starting point.
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<br><br><b><i>Lecture 1. Operating systems</i></b>
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In 6.828, the lectures in the first half of the course introduce the
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<br><br>
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PC hardware, the Intel x86, and then xv6. The lectures in the second
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The first lecture introduces both the general topic of
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half consider advanced topics using research papers; for some, xv6
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operating systems and the specific approach of 6.828.
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serves as a useful base for making discussions concrete. The lecture
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After defining “operating system,” the lecture
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notes are available from the 6.828 schedule page, and the chapters of
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examines the implementation of a Unix shell
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the commentary are below.
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to look at the details the traditional Unix system call interface.
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This is relevant to both xv6 and Jos: in the final
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Jos labs, students implement a Unix-like interface
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and culminating in a Unix shell.
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<br><br>
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<a href="l1.html">lecture notes</a>
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<a href="os-lab-1.pdf">OS abstractions slides</a>
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<br><br><b><i>Lecture 2. PC hardware and x86 programming</i></b>
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<h2>Xv6 commentary (rough)</h2>
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<br><br>
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This lecture introduces the PC architecture, the 16- and 32-bit x86,
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the stack, and the GCC x86 calling conventions.
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It also introduces the pieces of a typical C tool chain–compiler,
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assembler, linker, loader–and the Bochs emulator.
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<br><br>
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Reading: PC Assembly Language
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<br><br>
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Homework: familiarize with Bochs
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<br><br>
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<a href="l2.html">lecture notes</a>
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<a href="os-lab-2.pdf">x86 intro slides</a>
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<a href="x86-intro.html">homework</a>
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<br><br><b><i>Lecture 3. Operating system organization</i></b>
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<p>The chapters are rough drafts.
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<br><br>
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This lecture continues Lecture 1's discussion of what
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an operating system does.
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An operating system provides a “virtual computer”
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interface to user space programs.
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At a high level, the main job of the operating system
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is to implement that interface
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using the physical computer it runs on.
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<br><br>
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The lecture discusses four approaches to that job:
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monolithic operating systems, microkernels,
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virtual machines, and exokernels.
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Exokernels might not be worth mentioning
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except that the Jos labs are built around one.
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<br><br>
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Reading: Engler et al., Exokernel: An Operating System Architecture
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for Application-Level Resource Management
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<br><br>
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<a href="l3.html">lecture notes</a>
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<br><br><b><i>Lecture 4. Address spaces using segmentation</i></b>
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<p>Introduction yet to be written.<br>
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<br><br>
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<ul>
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This is the first lecture that uses xv6.
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<li>read with the code side by side
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It introduces the idea of address spaces and the
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<li>code references look like (xxxx) or (xxxx-yyyy) in small text.
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details of the x86 segmentation hardware.
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<li><a href="../src/xv6-rev4.pdf">this pdf</a> is the one with matching line numbers.
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It makes the discussion concrete by reading the xv6
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<li>each chapter starts with an introduction to the topic,
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source code and watching xv6 execute using the Bochs simulator.
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spends most of the text on code,
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<br><br>
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and then wraps up talking about how xv6
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Reading: x86 MMU handout,
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compares to real-world operating systems.
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xv6: bootasm.S, bootother.S, <a href="src/bootmain.c.html">bootmain.c</a>, <a href="src/main.c.html">main.c</a>, <a href="src/init.c.html">init.c</a>, and setupsegs in <a href="src/proc.c.html">proc.c</a>.
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</ul>
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<br><br>
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Homework: Bochs stack introduction
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<br><br>
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<a href="l4.html">lecture notes</a>
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<a href="os-lab-3.pdf">x86 virtual memory slides</a>
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<a href="xv6-intro.html">homework</a>
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<br><br><b><i>Lecture 5. Address spaces using page tables</i></b>
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<a href="unix.pdf">Chapter 0: Operating system interfaces</a>
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<br><br>
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<blockquote>
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This lecture continues the discussion of address spaces,
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The Unix system call interface. (rev 4)
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examining the other x86 virtual memory mechanism: page tables.
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</blockquote>
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Xv6 does not use page tables, so there is no xv6 here.
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Instead, the lecture uses Jos as a concrete example.
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An xv6-only course might skip or shorten this discussion.
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<br><br>
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Reading: x86 manual excerpts
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<br><br>
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Homework: stuff about gdt
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XXX not appropriate; should be in Lecture 4
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<br><br>
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<a href="l5.html">lecture notes</a>
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<br><br><b><i>Lecture 6. Interrupts and exceptions</i></b>
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<a href="boot.pdf">Chapter 1: Bootstrap</a>
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<br><br>
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<blockquote>
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How does a user program invoke the operating system kernel?
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From power on to kernel start. (rev 4)
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How does the kernel return to the user program?
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</blockquote>
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What happens when a hardware device needs attention?
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This lecture explains the answer to these questions:
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interrupt and exception handling.
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<br><br>
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It explains the x86 trap setup mechanisms and then
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examines their use in xv6's SETGATE (<a href="src/mmu.h.html">mmu.h</a>),
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tvinit (<a href="src/trap.c.html">trap.c</a>), idtinit (<a href="src/trap.c.html">trap.c</a>), <a href="src/vectors.pl.html">vectors.pl</a>, and vectors.S.
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<br><br>
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It then traces through a call to the system call open:
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<a href="src/init.c.html">init.c</a>, usys.S, vector48 and alltraps (vectors.S), trap (<a href="src/trap.c.html">trap.c</a>),
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syscall (<a href="src/syscall.c.html">syscall.c</a>),
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sys_open (<a href="src/sysfile.c.html">sysfile.c</a>), fetcharg, fetchint, argint, argptr, argstr (<a href="src/syscall.c.html">syscall.c</a>),
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<br><br>
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The interrupt controller, briefly:
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pic_init and pic_enable (<a href="src/picirq.c.html">picirq.c</a>).
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The timer and keyboard, briefly:
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timer_init (<a href="src/timer.c.html">timer.c</a>), console_init (<a href="src/console.c.html">console.c</a>).
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Enabling and disabling of interrupts.
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<br><br>
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Reading: x86 manual excerpts,
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xv6: trapasm.S, <a href="src/trap.c.html">trap.c</a>, <a href="src/syscall.c.html">syscall.c</a>, and usys.S.
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Skim <a href="src/lapic.c.html">lapic.c</a>, <a href="src/ioapic.c.html">ioapic.c</a>, <a href="src/picirq.c.html">picirq.c</a>.
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<br><br>
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Homework: Explain the 35 words on the top of the
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stack at first invocation of <code>syscall</code>.
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<br><br>
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<a href="l-interrupt.html">lecture notes</a>
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<a href="x86-intr.html">homework</a>
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<br><br><b><i>Lecture 7. Multiprocessors and locking</i></b>
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<a href="mem.pdf">Chapter 2: Processes</a>
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<br><br>
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<blockquote>
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This lecture introduces the problems of
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Memory and process allocation, segments, the first user process. (rev 4)
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coordination and synchronization on a
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</blockquote>
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multiprocessor
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and then the solution of mutual exclusion locks.
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Atomic instructions, test-and-set locks,
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lock granularity, (the mistake of) recursive locks.
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<br><br>
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Although xv6 user programs cannot share memory,
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the xv6 kernel itself is a program with multiple threads
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executing concurrently and sharing memory.
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Illustration: the xv6 scheduler's proc_table_lock (<a href="src/proc.c.html">proc.c</a>)
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and the spin lock implementation (<a href="src/spinlock.c.html">spinlock.c</a>).
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<br><br>
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Reading: xv6: <a href="src/spinlock.c.html">spinlock.c</a>. Skim <a href="src/mp.c.html">mp.c</a>.
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<br><br>
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Homework: Interaction between locking and interrupts.
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Try not disabling interrupts in the disk driver and watch xv6 break.
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<br><br>
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<a href="l-lock.html">lecture notes</a>
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<a href="xv6-lock.html">homework</a>
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<br><br><b><i>Lecture 8. Threads, processes and context switching</i></b>
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<a href="trap.pdf">Chapter 3: Traps</a>
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<br><br>
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<blockquote>
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The last lecture introduced some of the issues
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Low-level trap mechanism, trap handler, system call arguments, sbrk, fork.
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in writing threaded programs, using xv6's processes
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</blockquote>
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as an example.
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This lecture introduces the issues in implementing
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threads, continuing to use xv6 as the example.
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<br><br>
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The lecture defines a thread of computation as a register
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set and a stack. A process is an address space plus one
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or more threads of computation sharing that address space.
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Thus the xv6 kernel can be viewed as a single process
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with many threads (each user process) executing concurrently.
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<br><br>
|
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Illustrations: thread switching (swtch.S), scheduler (<a href="src/proc.c.html">proc.c</a>), sys_fork (<a href="src/sysproc.c.html">sysproc.c</a>)
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<br><br>
|
|
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Reading: <a href="src/proc.c.html">proc.c</a>, swtch.S, sys_fork (<a href="src/sysproc.c.html">sysproc.c</a>)
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<br><br>
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Homework: trace through stack switching.
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<br><br>
|
|
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<a href="l-threads.html">lecture notes (need to be updated to use swtch)</a>
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<a href="xv6-sched.html">homework</a>
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|
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<br><br><b><i>Lecture 9. Processes and coordination</i></b>
|
<a href="lock.pdf">Chapter 4: Locks</a>
|
||||||
<br><br>
|
<blockquote>
|
||||||
This lecture introduces the idea of sequence coordination
|
Locks and interrupts.
|
||||||
and then examines the particular solution illustrated by
|
</blockquote>
|
||||||
sleep and wakeup (<a href="src/proc.c.html">proc.c</a>).
|
|
||||||
It introduces and refines a simple
|
|
||||||
producer/consumer queue to illustrate the
|
|
||||||
need for sleep and wakeup
|
|
||||||
and then the sleep and wakeup
|
|
||||||
implementations themselves.
|
|
||||||
<br><br>
|
|
||||||
Reading: <a href="src/proc.c.html">proc.c</a>, sys_exec, sys_sbrk, sys_wait, sys_exec, sys_kill (<a href="src/sysproc.c.html">sysproc.c</a>).
|
|
||||||
<br><br>
|
|
||||||
Homework: Explain how sleep and wakeup would break
|
|
||||||
without proc_table_lock. Explain how devices would break
|
|
||||||
without second lock argument to sleep.
|
|
||||||
<br><br>
|
|
||||||
<a href="l-coordination.html">lecture notes</a>
|
|
||||||
<a href="xv6-sleep.html">homework</a>
|
|
||||||
|
|
||||||
<br><br><b><i>Lecture 10. Files and disk I/O</i></b>
|
<a href="sched.pdf">Chapter 5: Scheduling and coordination</a>
|
||||||
<br><br>
|
<blockquote>
|
||||||
This is the first of three file system lectures.
|
Scheduling, sleep and wakeup, pipes, wait and exit.
|
||||||
This lecture introduces the basic file system interface
|
</blockquote>
|
||||||
and then considers the on-disk layout of individual files
|
|
||||||
and the free block bitmap.
|
|
||||||
<br><br>
|
|
||||||
Reading: iread, iwrite, fileread, filewrite, wdir, mknod1, and
|
|
||||||
code related to these calls in <a href="src/fs.c.html">fs.c</a>, <a href="src/bio.c.html">bio.c</a>, <a href="src/ide.c.html">ide.c</a>, and <a href="src/file.c.html">file.c</a>.
|
|
||||||
<br><br>
|
|
||||||
Homework: Add print to bwrite to trace every disk write.
|
|
||||||
Explain the disk writes caused by some simple shell commands.
|
|
||||||
<br><br>
|
|
||||||
<a href="l-fs.html">lecture notes</a>
|
|
||||||
<a href="xv6-disk.html">homework</a>
|
|
||||||
|
|
||||||
<br><br><b><i>Lecture 11. Naming</i></b>
|
<a href="disk.pdf">Chapter 6: Buffer cache</a>
|
||||||
<br><br>
|
<blockquote>
|
||||||
The last lecture discussed on-disk file system representation.
|
Buffer cache and IDE disk driver.
|
||||||
This lecture covers the implementation of
|
</blockquote>
|
||||||
file system paths (namei in <a href="src/fs.c.html">fs.c</a>)
|
|
||||||
and also discusses the security problems of a shared /tmp
|
|
||||||
and symbolic links.
|
|
||||||
<br><br>
|
|
||||||
Understanding exec (<a href="src/exec.c.html">exec.c</a>) is left as an exercise.
|
|
||||||
<br><br>
|
|
||||||
Reading: namei in <a href="src/fs.c.html">fs.c</a>, <a href="src/sysfile.c.html">sysfile.c</a>, <a href="src/file.c.html">file.c</a>.
|
|
||||||
<br><br>
|
|
||||||
Homework: Explain how to implement symbolic links in xv6.
|
|
||||||
<br><br>
|
|
||||||
<a href="l-name.html">lecture notes</a>
|
|
||||||
<a href="xv6-names.html">homework</a>
|
|
||||||
|
|
||||||
<br><br><b><i>Lecture 12. High-performance file systems</i></b>
|
<a href="fsdata.pdf">Chapter 7: File system data</a>
|
||||||
<br><br>
|
<blockquote>
|
||||||
This lecture is the first of the research paper-based lectures.
|
Block in use bitmap, block allocation, inode structure, inode contents,
|
||||||
It discusses the “soft updates” paper,
|
directories, path names.
|
||||||
using xv6 as a concrete example.
|
</blockquote>
|
||||||
|
|
||||||
|
<a href="fscall.pdf">Chapter 8: File system calls</a>
|
||||||
|
<blockquote>
|
||||||
|
FIle descriptors, open, close, dup, read, write.
|
||||||
|
</blockquote>
|
||||||
|
|
||||||
|
<a href="exec.pdf">Chapter 9: Exec</a>
|
||||||
|
<blockquote>
|
||||||
|
Exec
|
||||||
|
</blockquote>
|
||||||
|
|
||||||
|
Appendix A: Low-level C and inline assembly
|
||||||
|
<blockquote>
|
||||||
|
Intro to C and inline assembly for people who only know Java (say).
|
||||||
|
Examples drawn entirely from xv6 source.
|
||||||
|
</blockquote>
|
||||||
|
|
||||||
|
Appendix B: Additional drivers.
|
||||||
|
<blockquote>
|
||||||
|
Keyboard, screen, probably MP hardware.
|
||||||
|
</blockquote>
|
||||||
|
|
||||||
|
<a name="v6"></a>
|
||||||
|
<h2>Unix Version 6</h2>
|
||||||
|
|
||||||
|
<p>6.828's xv6 is inspired by Unix V6 and by:
|
||||||
|
|
||||||
|
<ul>
|
||||||
|
|
||||||
|
<li>Lions' <i>Commentary on UNIX' 6th Edition</i>, John Lions, Peer to
|
||||||
|
Peer Communications; ISBN: 1-57398-013-7; 1st edition (June 14, 2000).
|
||||||
|
<ul>
|
||||||
|
|
||||||
|
<li>An on-line version of the <a
|
||||||
|
href="http://www.lemis.com/grog/Documentation/Lions/">Lions
|
||||||
|
commentary</a>, and <a href="http://v6.cuzuco.com/">the source code</a>.
|
||||||
|
|
||||||
|
|
||||||
|
<li>The v6 source code is also available <a
|
||||||
|
href="http://minnie.tuhs.org/UnixTree/V6/usr/sys/">online</a>
|
||||||
|
through <a
|
||||||
|
href="http://minnie.tuhs.org/PUPS/">the PDP Unix Preservation
|
||||||
|
Society</a>.
|
||||||
|
</ul>
|
||||||
|
|
||||||
|
</ul>
|
||||||
|
|
||||||
|
The following are useful to read the original code:
|
||||||
|
<ul>
|
||||||
|
<li><i>
|
||||||
|
The PDP11/40 Processor Handbook</i>, Digital Equipment Corporation, 1972.
|
||||||
|
<ul>
|
||||||
|
<li>A <a href="http://pdos.csail.mit.edu/6.828/2005/readings/pdp11-40.pdf">PDF</a> (made from scanned images,
|
||||||
|
and not text-searchable)
|
||||||
|
<li>A <a href="http://pdos.csail.mit.edu/6.828/2005/pdp11/">web-based
|
||||||
|
version</a> that is indexed by instruction name.
|
||||||
|
</ul>
|
||||||
|
|
||||||
|
</ul>
|
||||||
|
|
||||||
<h2>Feedback</h2>
|
<h2>Feedback</h2>
|
||||||
If you are interested in using xv6 or have used xv6 in a course,
|
If you are interested in using xv6 or have used xv6 in a course,
|
||||||
|
|
@ -346,12 +243,10 @@ we would love to hear from you.
|
||||||
If there's anything that we can do to make xv6 easier
|
If there's anything that we can do to make xv6 easier
|
||||||
to adopt, we'd like to hear about it.
|
to adopt, we'd like to hear about it.
|
||||||
We'd also be interested to hear what worked well and what didn't.
|
We'd also be interested to hear what worked well and what didn't.
|
||||||
<br><br>
|
<p>
|
||||||
Russ Cox (rsc@swtch.com)<br>
|
Russ Cox (rsc@swtch.com)<br>
|
||||||
Frans Kaashoek (kaashoek@mit.edu)<br>
|
Frans Kaashoek (kaashoek@mit.edu)<br>
|
||||||
Robert Morris (rtm@mit.edu)
|
Robert Morris (rtm@mit.edu)
|
||||||
<br><br>
|
<p>
|
||||||
You can reach all of us at 6.828-staff@pdos.csail.mit.edu.
|
You can reach all of us at 6.828-staff@pdos.csail.mit.edu.
|
||||||
<br><br>
|
|
||||||
</body>
|
|
||||||
</html>
|
|
||||||
|
|
|
||||||
339
web/index.txt
339
web/index.txt
|
|
@ -1,339 +0,0 @@
|
||||||
** Xv6, a simple Unix-like teaching operating system
|
|
||||||
Xv6 is a teaching operating system developed
|
|
||||||
in the summer of 2006 for MIT's operating systems course,
|
|
||||||
``6.828: Operating Systems Engineering.''
|
|
||||||
We used it for 6.828 in Fall 2006 and Fall 2007
|
|
||||||
and are using it this semester (Fall 2008).
|
|
||||||
We hope that xv6 will be useful in other courses too.
|
|
||||||
This page collects resources to aid the use of xv6
|
|
||||||
in other courses.
|
|
||||||
|
|
||||||
* History and Background
|
|
||||||
|
|
||||||
For many years, MIT had no operating systems course.
|
|
||||||
In the fall of 2002, Frans Kaashoek, Josh Cates, and Emil Sit
|
|
||||||
created a new, experimental course (6.097)
|
|
||||||
to teach operating systems engineering.
|
|
||||||
In the course lectures, the class worked through Sixth Edition Unix (aka V6)
|
|
||||||
using John Lions's famous commentary.
|
|
||||||
In the lab assignments, students wrote most of an exokernel operating
|
|
||||||
system, eventually named Jos, for the Intel x86.
|
|
||||||
Exposing students to multiple systems--V6 and Jos--helped
|
|
||||||
develop a sense of the spectrum of operating system designs.
|
|
||||||
In the fall of 2003, the experimental 6.097 became the
|
|
||||||
official course 6.828; the course has been offered each fall since then.
|
|
||||||
|
|
||||||
V6 presented pedagogic challenges from the start.
|
|
||||||
Students doubted the relevance of an obsolete 30-year-old operating system
|
|
||||||
written in an obsolete programming language (pre-K&R C)
|
|
||||||
running on obsolete hardware (the PDP-11).
|
|
||||||
Students also struggled to learn the low-level details of two different
|
|
||||||
architectures (the PDP-11 and the Intel x86) at the same time.
|
|
||||||
By the summer of 2006, we had decided to replace V6
|
|
||||||
with a new operating system, xv6, modeled on V6
|
|
||||||
but written in ANSI C and running on multiprocessor
|
|
||||||
Intel x86 machines.
|
|
||||||
Xv6's use of the x86 makes it more relevant to
|
|
||||||
students' experience than V6 was
|
|
||||||
and unifies the course around a single architecture.
|
|
||||||
Adding multiprocessor support requires handling concurrency head on with
|
|
||||||
locks and threads (instead of using special-case solutions for
|
|
||||||
uniprocessors such as
|
|
||||||
enabling/disabling interrupts) and helps relevance.
|
|
||||||
Finally, writing a new system allowed us to write cleaner versions
|
|
||||||
of the rougher parts of V6, like the scheduler and file system.
|
|
||||||
|
|
||||||
6.828 substituted xv6 for V6 in the fall of 2006.
|
|
||||||
Based on that experience, we cleaned up rough patches
|
|
||||||
of xv6 for the course in the fall of 2007.
|
|
||||||
Since then, xv6 has stabilized, so we are making it
|
|
||||||
available in the hopes that others will find it useful too.
|
|
||||||
|
|
||||||
6.828 uses both xv6 and Jos.
|
|
||||||
Courses taught at UCLA, NYU, Peking University, Stanford, Tsinghua,
|
|
||||||
and University Texas (Austin) have used
|
|
||||||
Jos without xv6; we believe other courses could use
|
|
||||||
xv6 without Jos, though we are not aware of any that have.
|
|
||||||
|
|
||||||
|
|
||||||
* Xv6 sources
|
|
||||||
|
|
||||||
The latest xv6 is [xv6-rev4.tar.gz].
|
|
||||||
We distribute the sources in electronic form but also as
|
|
||||||
a printed booklet with line numbers that keep everyone
|
|
||||||
together during lectures. The booklet is available as
|
|
||||||
[xv6-rev4.pdf].
|
|
||||||
The xv6 source code is licensed under the traditional <a href="http://www.opensource.org/licenses/mit-license.php">MIT license</a>;
|
|
||||||
see the LICENSE file in the source distribution.
|
|
||||||
|
|
||||||
xv6 compiles using the GNU C compiler,
|
|
||||||
targeted at the x86 using ELF binaries.
|
|
||||||
On BSD and Linux systems, you can use the native compilers;
|
|
||||||
On OS X, which doesn't use ELF binaries,
|
|
||||||
you must use a cross-compiler.
|
|
||||||
Xv6 does boot on real hardware, but typically
|
|
||||||
we run it using the Bochs emulator.
|
|
||||||
Both the GCC cross compiler and Bochs
|
|
||||||
can be found on the [../../2007/tools.html | 6.828 tools page].
|
|
||||||
|
|
||||||
|
|
||||||
* Lectures
|
|
||||||
|
|
||||||
In 6.828, the lectures in the first half of the course
|
|
||||||
introduce the PC hardware, the Intel x86, and then xv6.
|
|
||||||
The lectures in the second half consider advanced topics
|
|
||||||
using research papers; for some, xv6 serves as a useful
|
|
||||||
base for making discussions concrete.
|
|
||||||
This section describe a typical 6.828 lecture schedule,
|
|
||||||
linking to lecture notes and homework.
|
|
||||||
A course using only xv6 (not Jos) will need to adapt
|
|
||||||
a few of the lectures, but we hope these are a useful
|
|
||||||
starting point.
|
|
||||||
|
|
||||||
|
|
||||||
Lecture 1. Operating systems
|
|
||||||
|
|
||||||
The first lecture introduces both the general topic of
|
|
||||||
operating systems and the specific approach of 6.828.
|
|
||||||
After defining ``operating system,'' the lecture
|
|
||||||
examines the implementation of a Unix shell
|
|
||||||
to look at the details the traditional Unix system call interface.
|
|
||||||
This is relevant to both xv6 and Jos: in the final
|
|
||||||
Jos labs, students implement a Unix-like interface
|
|
||||||
and culminating in a Unix shell.
|
|
||||||
|
|
||||||
[l1.html | lecture notes]
|
|
||||||
[os-lab-1.pdf | OS abstractions slides]
|
|
||||||
|
|
||||||
|
|
||||||
Lecture 2. PC hardware and x86 programming
|
|
||||||
|
|
||||||
This lecture introduces the PC architecture, the 16- and 32-bit x86,
|
|
||||||
the stack, and the GCC x86 calling conventions.
|
|
||||||
It also introduces the pieces of a typical C tool chain--compiler,
|
|
||||||
assembler, linker, loader--and the Bochs emulator.
|
|
||||||
|
|
||||||
Reading: PC Assembly Language
|
|
||||||
|
|
||||||
Homework: familiarize with Bochs
|
|
||||||
|
|
||||||
[l2.html | lecture notes]
|
|
||||||
[os-lab-2.pdf | x86 intro slides]
|
|
||||||
[x86-intro.html | homework]
|
|
||||||
|
|
||||||
|
|
||||||
Lecture 3. Operating system organization
|
|
||||||
|
|
||||||
This lecture continues Lecture 1's discussion of what
|
|
||||||
an operating system does.
|
|
||||||
An operating system provides a ``virtual computer''
|
|
||||||
interface to user space programs.
|
|
||||||
At a high level, the main job of the operating system
|
|
||||||
is to implement that interface
|
|
||||||
using the physical computer it runs on.
|
|
||||||
|
|
||||||
The lecture discusses four approaches to that job:
|
|
||||||
monolithic operating systems, microkernels,
|
|
||||||
virtual machines, and exokernels.
|
|
||||||
Exokernels might not be worth mentioning
|
|
||||||
except that the Jos labs are built around one.
|
|
||||||
|
|
||||||
Reading: Engler et al., Exokernel: An Operating System Architecture
|
|
||||||
for Application-Level Resource Management
|
|
||||||
|
|
||||||
[l3.html | lecture notes]
|
|
||||||
|
|
||||||
|
|
||||||
Lecture 4. Address spaces using segmentation
|
|
||||||
|
|
||||||
This is the first lecture that uses xv6.
|
|
||||||
It introduces the idea of address spaces and the
|
|
||||||
details of the x86 segmentation hardware.
|
|
||||||
It makes the discussion concrete by reading the xv6
|
|
||||||
source code and watching xv6 execute using the Bochs simulator.
|
|
||||||
|
|
||||||
Reading: x86 MMU handout,
|
|
||||||
xv6: bootasm.S, bootother.S, bootmain.c, main.c, init.c, and setupsegs in proc.c.
|
|
||||||
|
|
||||||
Homework: Bochs stack introduction
|
|
||||||
|
|
||||||
[l4.html | lecture notes]
|
|
||||||
[os-lab-3.pdf | x86 virtual memory slides]
|
|
||||||
[xv6-intro.html | homework]
|
|
||||||
|
|
||||||
|
|
||||||
Lecture 5. Address spaces using page tables
|
|
||||||
|
|
||||||
This lecture continues the discussion of address spaces,
|
|
||||||
examining the other x86 virtual memory mechanism: page tables.
|
|
||||||
Xv6 does not use page tables, so there is no xv6 here.
|
|
||||||
Instead, the lecture uses Jos as a concrete example.
|
|
||||||
An xv6-only course might skip or shorten this discussion.
|
|
||||||
|
|
||||||
Reading: x86 manual excerpts
|
|
||||||
|
|
||||||
Homework: stuff about gdt
|
|
||||||
XXX not appropriate; should be in Lecture 4
|
|
||||||
|
|
||||||
[l5.html | lecture notes]
|
|
||||||
|
|
||||||
|
|
||||||
Lecture 6. Interrupts and exceptions
|
|
||||||
|
|
||||||
How does a user program invoke the operating system kernel?
|
|
||||||
How does the kernel return to the user program?
|
|
||||||
What happens when a hardware device needs attention?
|
|
||||||
This lecture explains the answer to these questions:
|
|
||||||
interrupt and exception handling.
|
|
||||||
|
|
||||||
It explains the x86 trap setup mechanisms and then
|
|
||||||
examines their use in xv6's SETGATE (mmu.h),
|
|
||||||
tvinit (trap.c), idtinit (trap.c), vectors.pl, and vectors.S.
|
|
||||||
|
|
||||||
It then traces through a call to the system call open:
|
|
||||||
init.c, usys.S, vector48 and alltraps (vectors.S), trap (trap.c),
|
|
||||||
syscall (syscall.c),
|
|
||||||
sys_open (sysfile.c), fetcharg, fetchint, argint, argptr, argstr (syscall.c),
|
|
||||||
|
|
||||||
The interrupt controller, briefly:
|
|
||||||
pic_init and pic_enable (picirq.c).
|
|
||||||
The timer and keyboard, briefly:
|
|
||||||
timer_init (timer.c), console_init (console.c).
|
|
||||||
Enabling and disabling of interrupts.
|
|
||||||
|
|
||||||
Reading: x86 manual excerpts,
|
|
||||||
xv6: trapasm.S, trap.c, syscall.c, and usys.S.
|
|
||||||
Skim lapic.c, ioapic.c, picirq.c.
|
|
||||||
|
|
||||||
Homework: Explain the 35 words on the top of the
|
|
||||||
stack at first invocation of <code>syscall</code>.
|
|
||||||
|
|
||||||
[l-interrupt.html | lecture notes]
|
|
||||||
[x86-intr.html | homework]
|
|
||||||
|
|
||||||
|
|
||||||
Lecture 7. Multiprocessors and locking
|
|
||||||
|
|
||||||
This lecture introduces the problems of
|
|
||||||
coordination and synchronization on a
|
|
||||||
multiprocessor
|
|
||||||
and then the solution of mutual exclusion locks.
|
|
||||||
Atomic instructions, test-and-set locks,
|
|
||||||
lock granularity, (the mistake of) recursive locks.
|
|
||||||
|
|
||||||
Although xv6 user programs cannot share memory,
|
|
||||||
the xv6 kernel itself is a program with multiple threads
|
|
||||||
executing concurrently and sharing memory.
|
|
||||||
Illustration: the xv6 scheduler's proc_table_lock (proc.c)
|
|
||||||
and the spin lock implementation (spinlock.c).
|
|
||||||
|
|
||||||
Reading: xv6: spinlock.c. Skim mp.c.
|
|
||||||
|
|
||||||
Homework: Interaction between locking and interrupts.
|
|
||||||
Try not disabling interrupts in the disk driver and watch xv6 break.
|
|
||||||
|
|
||||||
[l-lock.html | lecture notes]
|
|
||||||
[xv6-lock.html | homework]
|
|
||||||
|
|
||||||
|
|
||||||
Lecture 8. Threads, processes and context switching
|
|
||||||
|
|
||||||
The last lecture introduced some of the issues
|
|
||||||
in writing threaded programs, using xv6's processes
|
|
||||||
as an example.
|
|
||||||
This lecture introduces the issues in implementing
|
|
||||||
threads, continuing to use xv6 as the example.
|
|
||||||
|
|
||||||
The lecture defines a thread of computation as a register
|
|
||||||
set and a stack. A process is an address space plus one
|
|
||||||
or more threads of computation sharing that address space.
|
|
||||||
Thus the xv6 kernel can be viewed as a single process
|
|
||||||
with many threads (each user process) executing concurrently.
|
|
||||||
|
|
||||||
Illustrations: thread switching (swtch.S), scheduler (proc.c), sys_fork (sysproc.c)
|
|
||||||
|
|
||||||
Reading: proc.c, swtch.S, sys_fork (sysproc.c)
|
|
||||||
|
|
||||||
Homework: trace through stack switching.
|
|
||||||
|
|
||||||
[l-threads.html | lecture notes (need to be updated to use swtch)]
|
|
||||||
[xv6-sched.html | homework]
|
|
||||||
|
|
||||||
|
|
||||||
Lecture 9. Processes and coordination
|
|
||||||
|
|
||||||
This lecture introduces the idea of sequence coordination
|
|
||||||
and then examines the particular solution illustrated by
|
|
||||||
sleep and wakeup (proc.c).
|
|
||||||
It introduces and refines a simple
|
|
||||||
producer/consumer queue to illustrate the
|
|
||||||
need for sleep and wakeup
|
|
||||||
and then the sleep and wakeup
|
|
||||||
implementations themselves.
|
|
||||||
|
|
||||||
Reading: proc.c, sys_exec, sys_sbrk, sys_wait, sys_exec, sys_kill (sysproc.c).
|
|
||||||
|
|
||||||
Homework: Explain how sleep and wakeup would break
|
|
||||||
without proc_table_lock. Explain how devices would break
|
|
||||||
without second lock argument to sleep.
|
|
||||||
|
|
||||||
[l-coordination.html | lecture notes]
|
|
||||||
[xv6-sleep.html | homework]
|
|
||||||
|
|
||||||
|
|
||||||
Lecture 10. Files and disk I/O
|
|
||||||
|
|
||||||
This is the first of three file system lectures.
|
|
||||||
This lecture introduces the basic file system interface
|
|
||||||
and then considers the on-disk layout of individual files
|
|
||||||
and the free block bitmap.
|
|
||||||
|
|
||||||
Reading: iread, iwrite, fileread, filewrite, wdir, mknod1, and
|
|
||||||
code related to these calls in fs.c, bio.c, ide.c, and file.c.
|
|
||||||
|
|
||||||
Homework: Add print to bwrite to trace every disk write.
|
|
||||||
Explain the disk writes caused by some simple shell commands.
|
|
||||||
|
|
||||||
[l-fs.html | lecture notes]
|
|
||||||
[xv6-disk.html | homework]
|
|
||||||
|
|
||||||
|
|
||||||
Lecture 11. Naming
|
|
||||||
|
|
||||||
The last lecture discussed on-disk file system representation.
|
|
||||||
This lecture covers the implementation of
|
|
||||||
file system paths (namei in fs.c)
|
|
||||||
and also discusses the security problems of a shared /tmp
|
|
||||||
and symbolic links.
|
|
||||||
|
|
||||||
Understanding exec (exec.c) is left as an exercise.
|
|
||||||
|
|
||||||
Reading: namei in fs.c, sysfile.c, file.c.
|
|
||||||
|
|
||||||
Homework: Explain how to implement symbolic links in xv6.
|
|
||||||
|
|
||||||
[l-name.html | lecture notes]
|
|
||||||
[xv6-names.html | homework]
|
|
||||||
|
|
||||||
|
|
||||||
Lecture 12. High-performance file systems
|
|
||||||
|
|
||||||
This lecture is the first of the research paper-based lectures.
|
|
||||||
It discusses the ``soft updates'' paper,
|
|
||||||
using xv6 as a concrete example.
|
|
||||||
|
|
||||||
|
|
||||||
* Feedback
|
|
||||||
|
|
||||||
If you are interested in using xv6 or have used xv6 in a course,
|
|
||||||
we would love to hear from you.
|
|
||||||
If there's anything that we can do to make xv6 easier
|
|
||||||
to adopt, we'd like to hear about it.
|
|
||||||
We'd also be interested to hear what worked well and what didn't.
|
|
||||||
|
|
||||||
Russ Cox (rsc@swtch.com)<br>
|
|
||||||
Frans Kaashoek (kaashoek@mit.edu)<br>
|
|
||||||
Robert Morris (rtm@mit.edu)
|
|
||||||
|
|
||||||
You can reach all of us at 6.828-staff@pdos.csail.mit.edu.
|
|
||||||
|
|
||||||
BIN
web/lock.pdf
Normal file
BIN
web/lock.pdf
Normal file
Binary file not shown.
BIN
web/mem.pdf
Normal file
BIN
web/mem.pdf
Normal file
Binary file not shown.
70
web/mkhtml
70
web/mkhtml
|
|
@ -1,70 +0,0 @@
|
||||||
#!/usr/bin/perl
|
|
||||||
|
|
||||||
my @lines = <>;
|
|
||||||
my $text = join('', @lines);
|
|
||||||
my $title;
|
|
||||||
if($text =~ /^\*\* (.*?)\n/m){
|
|
||||||
$title = $1;
|
|
||||||
$text = $` . $';
|
|
||||||
}else{
|
|
||||||
$title = "Untitled";
|
|
||||||
}
|
|
||||||
|
|
||||||
$text =~ s/[ \t]+$//mg;
|
|
||||||
$text =~ s/^$/<br><br>/mg;
|
|
||||||
$text =~ s!\b([a-z0-9]+\.(c|s|pl|h))\b!<a href="src/$1.html">$1</a>!g;
|
|
||||||
$text =~ s!^(Lecture [0-9]+\. .*?)$!<b><i>$1</i></b>!mg;
|
|
||||||
$text =~ s!^\* (.*?)$!<h2>$1</h2>!mg;
|
|
||||||
$text =~ s!((<br>)+\n)+<h2>!\n<h2>!g;
|
|
||||||
$text =~ s!</h2>\n?((<br>)+\n)+!</h2>\n!g;
|
|
||||||
$text =~ s!((<br>)+\n)+<b>!\n<br><br><b>!g;
|
|
||||||
$text =~ s!\b\s*--\s*\b!\–!g;
|
|
||||||
$text =~ s!\[([^\[\]|]+) \| ([^\[\]]+)\]!<a href="$1">$2</a>!g;
|
|
||||||
$text =~ s!\[([^ \t]+)\]!<a href="$1">$1</a>!g;
|
|
||||||
|
|
||||||
$text =~ s!``!\“!g;
|
|
||||||
$text =~ s!''!\”!g;
|
|
||||||
|
|
||||||
print <<EOF;
|
|
||||||
<!-- AUTOMATICALLY GENERATED: EDIT the .txt version, not the .html version -->
|
|
||||||
<html>
|
|
||||||
<head>
|
|
||||||
<title>$title</title>
|
|
||||||
<style type="text/css"><!--
|
|
||||||
body {
|
|
||||||
background-color: white;
|
|
||||||
color: black;
|
|
||||||
font-size: medium;
|
|
||||||
line-height: 1.2em;
|
|
||||||
margin-left: 0.5in;
|
|
||||||
margin-right: 0.5in;
|
|
||||||
margin-top: 0;
|
|
||||||
margin-bottom: 0;
|
|
||||||
}
|
|
||||||
|
|
||||||
h1 {
|
|
||||||
text-indent: 0in;
|
|
||||||
text-align: left;
|
|
||||||
margin-top: 2em;
|
|
||||||
font-weight: bold;
|
|
||||||
font-size: 1.4em;
|
|
||||||
}
|
|
||||||
|
|
||||||
h2 {
|
|
||||||
text-indent: 0in;
|
|
||||||
text-align: left;
|
|
||||||
margin-top: 2em;
|
|
||||||
font-weight: bold;
|
|
||||||
font-size: 1.2em;
|
|
||||||
}
|
|
||||||
--></style>
|
|
||||||
</head>
|
|
||||||
<body bgcolor=#ffffff>
|
|
||||||
<h1>$title</h1>
|
|
||||||
<br><br>
|
|
||||||
EOF
|
|
||||||
print $text;
|
|
||||||
print <<EOF;
|
|
||||||
</body>
|
|
||||||
</html>
|
|
||||||
EOF
|
|
||||||
BIN
web/sched.pdf
Normal file
BIN
web/sched.pdf
Normal file
Binary file not shown.
BIN
web/trap.pdf
Normal file
BIN
web/trap.pdf
Normal file
Binary file not shown.
BIN
web/unix.pdf
Normal file
BIN
web/unix.pdf
Normal file
Binary file not shown.
Loading…
Reference in a new issue