1. Using Virtual Machines to Teach CS-502 Operating Systems
PEDS
November 6, 2006
Assumptions:
Graduate level
Operating Systems
Making Choices about operation systems
Why a micro-century? …just about enough time for one concept
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

2. Using Virtual Machines to Teach CS-502
Problem
Project work in Operating Systems course has a “make believe” quality about it
Fossil Lab not available to M. Sc. Students
Part-time students not present on campus — so could not use Fossil Lab even if available
User space projects do not demystify the system infrastructure
Too much of what OS does is still hidden from students
No practical experience about insides of OS
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

3. Using Virtual Machines to Teach CS-502
Approach
Create VMware virtual machine with Linux
Assign programming projects inside kernel
Expose
Workings of an OS kernel
Differences between working inside of OS and outside
Practical experience with principles that we teach
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

4. Using Virtual Machines to Teach CS-502
This Presentation
An interim report on experiences in CS-502 during Fall 2006
Practical problems with using VMware
Successes and missteps
Pedagogical issues
Problem assignments
Grading
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

5. Using Virtual Machines to Teach CS-502
Starting out
Created VMware virtual machine on csopt4
SUSE Linux 9.3
same as CS Department
5 GByte hard drive, 256 MByte RAM, single processor
NAT (Network Address Translation) networking
VMware Tools installed
Students copy virtual machine to own directories
Minor adjustment to change Ethernet MAC address
Students access remotely on or off campus via VMware Console (aka VMware client)
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

6. Panic in system team!
20-21 registered students, implies 100+ gigabytes on /xtra_space
Close to total available space; Pressure on disk drives; Pressure on processors
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

7. Using Virtual Machines to Teach CS-502
Another Problem
VMware console is awkward and jerky to use from off campus
To the point of being impractical to use
Affects about ½ to ¾ of students
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

8. Solution (to both problems)
Created a virtual machine using my own copy of VMware Workstation on my Pentium at home
Includes VMware Tools (needed for display)
Copied onto DVDs, distributed to class
Also on CDs; also available for download from csopt4
Most students downloaded VMware Player
Freeware player capable of running virtual machines created on other VMware products
No snapshots, no reconfiguration of VM, etc.
Three students chose to remain on csopt4
One elected to switch to VMware Player for next project
Two students created own virtual machines on Macintosh Parallels (Intel platform)
Instructions published on course web-site
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

9. Using Virtual Machines to Teach CS-502
Recommended Resource
Robert Love, Linux Kernel Development, 2nd edition, Novell Press, 2005
Other kernel development books are available
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

10. Using Virtual Machines to Teach CS-502
Practical Issues
Networking — bridged vs. NAT
Wireless users on campus must use NAT
Macintosh Parallels does not offer NAT
Must use web-based turnin program
CCC turnin too awkward from virtual machine
Incompatible virtual machines
Pentium and Opteron (csopt4) are different kinds of CPUs
Virtual machines constructed on one do not run on other
Kernel projects developed on one are incompatible at source code level with those of the other
Network connections are fragile
Seem to fail when new kernels are installed; no solution yet
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

11. Using VMware Player on a Windows PC
Full Linux with
KDE desktop environment, Mozilla browser, etc.
GUI based system administration (YaST) & other tools
Uniform compiler, build environment, etc.
VM runs either in window or full-screen
Rapid switch between Windows and VM
First class citizen on my home network
Good, responsive performance
even with other Windows applications active
Missing: cut, copy, paste between Windows and Linux
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

12. Using Virtual Machines to Teach CS-502
Building Linux Kernel
Create copy-on-write tree
cp –al /usr/src/linux kernelSrc
Edit kernel by replacing files within tree
Automatic with EMACS, patch
Needs extra step with vi, kwrite, Eclipse, etc.
Build to separate build tree
make O=~/kernelBuild xconfig (or oldconfig) make O=~/kernelBuild
Install
make O=~/kernelBuild modules_install install
Automatically installs in grub
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

13. Using Virtual Machines to Teach CS-502
Build performance
Entire kernel from scratch
Approx 1 hour on 3-GHz, 1-Gigabyte Pentium
Approx 40 minutes on csopt4 Opteron
Rebuild with new label
~ 30 minutes on 3-GHz, 1-Gigabyte Pentium
< 20 minutes on csopt4 Opteron
Rebuild with same label (make oldconfig)
5 minutes on 3-GHz, 1-Gigabyte Pentium
< 2 minutes on csopt4 Opteron
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

14. Submitting Kernel Project
Create patch file
diff -urN /usr/src/linux kernelSrc
Submit
patch file
test program(s)
Makefile to build test programs
Write-up, etc.
Notes:
Building to separate build-tree keeps junk out of patch file
Symbolic link in original kernel source adds junk to patch
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

15. Preparing to Grade a Kernel Project
Build entire kernel (on each machine type)
cp –al /usr/src/linux kernelSrc cd kernelSrc make O=~/kernelBuild xconfig make O=~/kernelBuild
Fetch students’ submissions from turnin
Expand to separate directories for each student
Take snapshot of virtual machine
Allows restoring to same state for each student
Keeping same label on kernel minimizes rebuild time
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

16. Grading Kernel Project
Restore virtual machine to snapshot for each student
Patch and rebuild
cd kernelSrc patch –p1 < {student’s patch file} make O=~/kernelBuild oldconfig make O=~/kernelBuild
Install, reboot, and test
make O=~/kernelBuild modules_install install reboot cd {student’s directory} make run tests
About minutes to actually build and test per student
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

17. Using Virtual Machines to Teach CS-502
Problems and Issues
Building and installing new kernel seems to make network fail
May be due to VMware Tools vs. kernel modules
Installation order is critical (modules must be 1st!)
make O=~/kernelBuild modules_install install
make install assumes new kernel is default
Can be corrected by copying and modifying scripts
/sbin/installkernel and /sbin/mkinitrd
printk() output doesn’t appear on syslog
Seems to be filtered; unable to find correct settings
Use cat /proc/kmsg or /bin/dmesg instead
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

18. Problems and Issues (continued)
printf semantics don’t work in printk
Ability to embed “%d” in strings, etc.
Plenty of examples in kernel where it is supposed to work!
make gconfig doesn’t work
Superior interface for configuration
Some Gnome libraries are missing from virtual machine; don’t know which
Grader needs access to tools
VMware Workstation, PC big enough to run it
Printing in general
Works fine in my home network via CUPS
Haven’t been able to set up in CS Department
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

19. Problems and Issues (continued)
No practical way for students to back up their work
Untried: ability to map to drives on other machines
Possibility: USB flash drive
Alternative: create a virtual machine with two hard disks (one for kernel, one for user)
This problem needs a solution — the whole idea of the virtual machine is to be able to safely make mistakes!
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

20. Using Virtual Machines to Teach CS-502
Project Assignments
Project #1 completed
Add a system call and use printk()
Project #2 in progress
Mailbox and messaging system
Optionally use kdb
Project #3 to be assigned
TBD, probably Page replacement
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

21. Project #1 — Add a system call
Learn to build kernel
Claypool, “Linux dabbling”
Add “Hello, world” system call, use printk
Silbershatz, Chapter 2 project
Add getprinfo system call
Prof. Jason Nieh (Columbia Univ)
Three weeks total
Could be reduced to two weeks when bugs are ironed out
Educational value
Kernels are different (and difficult)
A lot of fumbling before running
Overcome the intimidation of reaching inside something “magic”
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

22. Project #2 – Mailbox and Message system
Patterned after similar user-space projects of previous terms
Lauer, Tabloski, Wills, etc.
Educational value
Memory allocation, esp. in kernel
Synchronization via semaphores, reader-writer locks
Difference between kernel code and user-space wrapper
This turns out to be a really hard project
Even in user space!
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

23. Using Virtual Machines to Teach CS-502
Other Kernel Projects
Nieh
Thread synchronization
GWRR scheduling
Page replacement algorithm
Access control lists for files
Claypool
Linux Dabbling
Background scheduling policy
Hidden processes
Process, thread accounting
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502

24. Using Virtual Machines to Teach CS-502
Teaching Goals
Kernel is not magic
Kernel is not like any other program
Cement the fundamental concepts of an operating system course
Ability to say at a job interview:–
“Yes indeed, I have worked inside a major OS kernel.”
PEDS, November 6, 2006
Using Virtual Machines to Teach CS-502