Project: A Simple Operating System

1. Overview
2. Assessment
3. Milestones
4. Resources
5. A warning
6. Demonstrations

Overview

The aim of the assignment is to implement a simple operating system (SOS) server on top of the L4 microkernel. The SOS server is expected provide a specified system call interface to its clients. (Specified in sos.h) The project will be completed by groups of 2 students. This is a challenging project. You have been warned!. The project is to be completed using the facilities in the ASysT Lab.

Assessment

More than half the marks for the project are obtained for timely and complete demonstration of intermediate milestones. These milestones will be demonstrated in the lab each week. When demonstrating your solution you should be able to

• show a working solution,
• explain how to code you have written works, and
• explain any design decisions you made.

The remaining marks will be determined by our assessment of your overall project and documentation. The assessment involves:

• testing your code and its conformance with the specifications,
• inspecting your code as to how well and efficiently it is written, and
• perusing your documentation as to its completeness, appropriateness and consistency with your implementation.

Milestones

M0: Familiarisation

Due: Week 2
Marks: 4 (-1 per week late, discontinue course if more than one week late)
Milestone 0 involves familiarising yourself with the provided source code, and build system, and then writing a simple IPC protocol. This mileston should be done individually. Further milestones are done in groups.

M1: Memory manager

Due: Week 3
Marks: 4 (-1 per week late, discontinue course if more than one week late)
Design and implement a simple frame table.

M2: A pager

Due: Week 4
Marks: 4 (-1 per week late)
Design and implement a simple pager based on the existing pager and the memory manager completed in M1.

M3: System call interface

Due: Week 5
Marks: 4 (-1 per week late)
Design and implement the system call interface for your operating system.

M4: A clock driver

Due: Week 6
Marks: 4 (-1 per week late)
Write a simple device driver for the timer functions available on the GT chip.

M5: Implement filesystem

Due: Week 8
Marks: 4 (-1 per week late)
Using the provided code implement the filesystem related system calls.

M6: Demand paging

Due: Week 9
Marks: 4 (-1 per week late)
Implement the demand paging in your operating system.

M7: Process management

Due: Week 10
Marks: 4 (-1 per week late)
Design and implement process management. You should implement the process_* system calls.

M8: ELF Loading

Due: Week 12
Marks: 24 (-4 per week late)
Extend your process management code to handle loading ELF files. This is your final milestone, and you should be prepared to demonstrate you entire system working at this stage.

M9: Documentation

Due: Week 13
Marks: 9 (-2 per week late)
Complete the documentation for your project.

Advanced Components (aka Stuff for Masochists)

The following features, if demonstrated and submitted together with you Milstone 9, will give bonus marks. (2 marks each, -1 per week late.)

Shared memory

Implement the shared memory via the share_vm() system call and demonstrate operation with some application which has processes communicating via shared memory.

Clocked driver loaded from file system

Rather than loading your clock driver from the boot imager, load it from the file system and run it as a separate L4 task.

Filesystem caching

Reserve a part of RAM as a file system cache. Implement caching of directory information and file data, as well as read-ahead, to improve file system performance.

Dynamic filesystem (only valid with file system caching)

Have your SOS file system behave correctly even if files are added/removed in the Unix file system while your SOS is running. Do this without significantly degrading performance.

Disk file system

Sulima supports a simulated IDE device, and (a small number of) IDE controllers and disks are available to be installed in the MIPS machines. Port or write an IDE driver to your OS and write a proper on-disk file system.

Resources

• AOS Design Guide
• GNU make is used to build SOS. You should be familar with how it works.
• CVS documentation
• L4 reference manual
• L4 user manual (still in draft form)
• DITE reference
• L4 source browser
• SOS source browser
• Project FAQ
• Debugging on L4
• Sulima
• Provided framework overview
• Asyst lab info
• MIPS R4700 reference
• MIPS R4000 user manual
• GT64111 Documentation

Warning!

Some students are tempted to write some tricky or obscure code for these projects. Other students run into problems by trying to do too much.

I can only reiterate that the debugging environment you have on the U4600s is extremely spartanic. You will not do yourself a favour by writing obscure or particularly tricky code. You'll most likely end up getting hoplessly tangled up in your own code. Don't do this.

Write your code as clearly, obviously and straightforward as possible. This is the best safeguard against obscure bugs. I believe that the project is challenging enough as it is, there is no need to make it harder.

Furthermore, when doing the final project marking I will obviously not look with much sympathy upon code I find difficult to understand.

The same applies for implementing features beyond the project specifications. You are welcome to do this, but, in your own interest, you are strongly advised to implement the required features first. First make it work, then go for the extras! Most of the (very few) students who have failed the course to date have ignored this rule — at their peril!

Demonstration and Submission of Milestones

Your are to show that your project passes the milestone requirements by demonstrating its operation to the demonstrator during the allocated time during the week the milestone is due.

In addition, you are to submit your source code using the give system.

You should submit all your code, including makefiles etc. This means that you should create a tar file of your submission. eg:

tar cvf cs9242-m0.tar.gz sos
give cs9242 m0 cs9242-m0.tar.gz

Only one member of the group needs to submit.

Notes

• All students belonging to the group must be present during the demonstration.
• Only one group member needs to submit the source code electronically.
• The demonstrator will ask you questions on your implementation to make sure that you understand what you are presenting. Your responses to this questioning will have a major impact on the mark you will be receiving.
  Zero marks will be awarded if you cannot demonstrate a basic understanding of your solution. A trial-and-error approach will not get you anywhere.
• In most cases all members of a group will receive the same mark. However, in cases where there is a clear difference in understanding of the problem and its solution between the group members, we will differentiate the marks awarded.
• Milestone 0 is mainly intended to ensure that you understand the basics, and generally students are asked to improve their code rather than docking off marks.
• This is different for the later milestones, which serve to ensure that you have met the specified target. Marks will be deducted for incomplete or faulty implementations. In these milestones we will not look at your code but only check that you seem to have have implemented the requested functionality. It is up to you to supply a driver program which demonstrates this.
• Marks for milestones 0 to 8 are awarded at demonstration time. Marks for milestones 9, 10 (and potential bonus) are only awarded after our testing and code inspection. However, you will still have to do the demonstration. This is to avoid problems with obviously incomplete or non-compliant code.
• Milestone 8, besides demonstrating the functionality, will require you to submit the full code in a form we can use for automatic testing. This means that you will have removed all debugging output, none of your OS or library code should write anything (other than what clients write to the console).
• Milestone 9, the documentation, will be submitted in hardcopy as well as electronically as a ASCII text file (with or without TeX or troff formatting commands, but definitively not a word document or anything the like).