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Project: A Simple Operating System
These pages outline what you will be expected to implement for the
project. While some minor details may change during session, this
has been a successful format for a number of years. It is a good
idea to start thinking early and try to understand the full
assignment and ask any questions you have about structure and
problems early.
- Overview
- Assessment
- Milestones
- Resources
- A warning
- Demonstrations
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 to 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 Slug Lab.
About half the marks for the project are obtained for
timely and complete demonstration of intermediate
milestones (M0–M7). 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 the 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.
- M0: Familiarisation
-
Due: Week 2
Marks: 4 (-1 for one 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
milestone should be done individually. Further milestones are
done in groups.
- M1: Memory manager
-
Due: Week 3
Marks: 4 (-1 if one 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: Implement filesystem
-
Due: Week 6
Marks: 4 (-1 per week late)
Using the provided code implement the filesystem related system calls.
- M5: A timer driver and benchmarking
-
Due: Week 7
Marks: 4 (-1 per week late)
Write a simple device driver for the timers available on the
IXP420, and use it to benchmark your filesystem.
- M6: Demand paging
-
Due: Week 8
Marks: 4 (-1 per week late)
Implement 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 11
Marks: 4 (-1 per week late)
Extend your process management code to handle loading ELF files. This
is your last demo; your entire system should be working at this stage.
- M9: Documentation
-
Due: Week 12, Monday 23:59, 11 Oct.
Marks: 9 (-2 per week late) docs, 20 (-3 per week late) code
Complete the documentation for your project. You also have a chance to
clean up your codebase for your final submission.
This milestone does not involve a lab demo.
The following features, if demonstrated and submitted
together with your Milestone 8, will give bonus
marks. (2 marks each, -1 per week late.)
- Shared memory
- Implement shared memory via the
share_vm()
system call and demonstrate operation with some application
which has processes communicating via shared memory.
- Clock driver loaded from file system
- Rather than loading your clock driver from the boot image,
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.
Kernel Bugs
In addition, there are bonus marks for finding kernel
bugs (not library bugs!) Specifically, the first student who
reproducibly proves a previously unknown bug in the L4 kernel will
receive two bonus marks.
A student who provides a working patch to a kernel bug
(irrespective whether the bug was found by them or someone else)
will receive a further two bonus marks.
No late penalty applies for kernel bonus marks, although the
claim must be made no later than the conclusion of the exam.
Notes on Bonus Marks
- No bonus marks will be awarded on a
“sympathy” basis for a
well-intended attempt — your code implementing a bonus feature must
completely work (except for maybe some minor details) in order
to qualify for a bonus.
- The maximum number of bonus marks that can be accumulated is
10, no matter how they have been earned.
- Bonus marks (for L4 bugs or for doing a bonus component of the
project) can be used to make up for lost project marks,
up to the maximum project mark possible (65). If your total
project marks, including bonus, exceeds 65, the surplus can be
used at half face value for marks lost in the exam.
- Bonus marks cannot be used if the raw exam mark is less
than 40%, a 40% raw exam mark is an absolute prerequisite
for passing the course!
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
Slug is extremely spartan. 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!
You 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 changes, including makefiles
etc. This means that you should create a tar file which includes
any directories containing changed code. eg:
cd aos-2010
tar -zcvf ../m0.tar.gz sos sosh tty_test Makefile
give cs9242 m0 ../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 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 milestone 9 (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 9, 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/ODF document or anything the
like).
Instead of hardcopy, to save trees, you can submit a PDF.
Last modified:
06 Sep 2010.
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