Operating Systems COMP 310 – ECSE 427 McGill University
Vybihal & Balmau Final Exam Project Page 1 of 10
COMP 310 – ECSE 427 Winter 2021
Take Home Final Exam Project
Start: April 7, 2021 9:00 EDT, Due: April 21, 2021 9:00 EDT

Instructions
• IMPORTANT: You must answer and sign Question 1 for us to grade your Question 2. If Question
1 is not completed, we will not grade Question 2 even if you submitted a solution.

• This is an individual, open-book, closed-internet exam.
Therefore, the following sources are not permitted:
o You are not permitted to get help from friends or strangers.
o You are not permitted to use any online tools, chat services, or websites like Chegg, Reddit
and Stack Overflow, or other such places.
o You are not permitted to use the internet in any way.
o You cannot use course material from any other course.
You are permitted to access the following course materials:
o myCourses and mimi.
o You are permitted to use the textbook and your course notes.
o You are permitted to access the labs, assignments, and lectures of this course.
• There are no extensions for this assignment. You cannot submit a solution to this test after the
due date and time.
• Partial marks are awarded, according to the marking scheme we provide.
• We will use MOSS to verify that the code you wrote is unique to you. We will check your code to
online resources that have similar code in case you copied from those resources.
• If you have questions, the instructors will be available during these 14 days on Piazza (please post
a private message – public questions for this test will be deleted).
• The instructors will have office hours on Zoom where you can ask questions. The schedule and
Zoom links have been published on myCourses.


Grading

Question 1 …………………………………………………………………………………… YES / NO

Question 2 …………………………………………………………………………………… _______ / 40
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Question 1 – Academic Integrity

IMPORTANT: Question 2 will not be graded if Question 1 is not signed and submitted.

McGill University values academic integrity. Therefore, all students must understand the meaning and
consequences of cheating, plagiarism and other academic offences under the Code of Student Conduct
and Disciplinary Procedures (see www.mcgill.ca/students/srr/honest/ for more information, approved
by Senate on 29 January 2003).
Please affirm the following statement:
I have neither given nor received unauthorized aid on this exam and I agree to adhere to the
specific Terms and Conditions that govern this exam.
Sign in this box:




Please sign in the above box, and then take a picture or scan this page or sign using a PDF signature,
and upload this signed page to the final exam Assignment submission box.

Note: The submission box accepts multiple uploads, so you will be able to submit your solution to
Question 2 after you upload the signed picture of Question 1. Please do that now.



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Vybihal & Balmau Final Exam Project Page 3 of 10
Question 2 – Programming Assignment

Preliminary Notes

Problems. The exam consists of 4 problems, each worth 10 points:
• Three problems contained in this document, which are common to all students.
• One randomized problem. You will find the 4th problem in the myCourses Quiz tool entitled Final
Exam Project Question.
• We highly recommend attempting to solve the problems in the given order.

Codebase. You have been given a codebase to work from. This codebase is a valid solution for Assignment
#4. Please take some time to get accustomed to this codebase, as you will need to modify this given
codebase to solve the 4 problems. You are allowed (and encouraged) to reuse any functions and data
structures provided in the codebase to implement the new functionality.
Do not use your own OS developed in the assignments for this exam.
In this exam you will be asked to modify the given codebase to implement four additional script
commands. Testfile scripts for each problem are provided to you in this document (and in the Quiz tool
for the 4th problem). You have also been provided special source files and code hooks where you must
implement the extra functionality – you will find more details in the problem text.
To compile the codebase, run the provided ./recompile.sh script.
The following commands should run on mimi with the provided codebase. Compile the codebase and run
the commands below (also available in TESTFILE.txt provided to you) now:
1. mount partition0 10 5
2. write file1 [hello world test]
3. read file1 var
4. print var
5. quit
The command on line 4 should display: hello world test
IMPORTANT: If the codebase fails to execute, contact Prof. Balmau or Prof. Vybihal immediately.

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Vybihal & Balmau Final Exam Project Page 4 of 10
Submitting your solutions

All solutions (even to the problem in the Quiz tool), must be submitted to the submission box in the
Assignment tool. The submission box accepts multiple submissions. We strongly recommend answering
this exam in the following order:

1. Sign and upload Question 1 to the Assignment submission box for this exam (you should have
done so already!). If you do not complete Question 1, we will not grade Question 2.
2. Upload the solutions to Problems 1, 2, and 3 presented in this document to the Assignment
submission box for this exam. Remember that partial marks are given.
3. After completing step 2, go to the Quiz tool and get your final randomized Problem 4. When
entering the quiz, your randomized question will be assigned to you. We suggest you take a
screenshot of the final question and save the screenshot to your computer.
4. The Quiz tool will present Problem 4 as a true/false question. After reading it and taking the screen
shot, select true, and submit the quiz.
5. Press submit on the Quiz tool to prove to us that you looked at the Problem 4 question. If you
did not press submit, we will not grade your solution to Problem 4.
6. Upload the solution to Problem 4 to the submission box in the Assignment tool for this exam.

You have now completed the exam!

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Vybihal & Balmau Final Exam Project Page 5 of 10
Problem 1: Open Command [10 points]

Change the provided codebase so that you cannot read or write to a file unless you initially open the file.
Trying to read or write to a file without first opening the file will generate an error message. The syntax
of your open command is:
open_EXAM filename
• The file_ID_in_active_file_table parameter is an integer that corresponds to the array
cell index in the active file table where the user wishes to open the file.
• The filename parameter is the name of the file that will be opened by the open_EXAM
command.
You will also need to adjust change the read and write commands. Do not modify the read and write
commands that were given to you. Instead, add the following 2 commands:
read_EXAM var
• The file_ID_in_active_file_table parameter is an integer that corresponds to the array
cell index in the active file table where the file has been opened.
• The var parameter is a shell variable into which the contents of the file will be read.
write_EXAM [alphanumeric strings separated by
spaces]
• The file_ID_in_active_file_table parameter is an integer that corresponds to the array
cell index in the active file table where the file has been opened.
• The [] square brackets, as before, contain alphanumeric strings separated by spaces. The contents
inside the brackets will be written to the file.
Code hooks in the codebase
You were provided with three function templates in interpreter.c called openCommandEXAM(),
readCommandEXAM(), and writeCommandEXAM(). You have also been provided with two empty files,
DISK_driver_problem1.c (and .h). Use these three places to implement the open_EXAM,
read_EXAM, and write_EXAM functionality. Feel free to expose other functions and data structures
already existent in the codebase to your DISK_driver_problem1 files. You should be able to complete
your implementation by only modifying these three locations. However, if you absolutely need to make
modifications elsewhere in the codebase, make a note in the README file, explaining why.
Implementation details
• The open_EXAM command is used to setup the data structures in the OS and locate the file in
the partition.
• When a file is opened the pointer to the file is initialized to point to the beginning of the file.
• To make things easy, the open_EXAM command has an index number that refers to the cell of
the active file table.
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• The read_EXAM and write_EXAM commands will reference that index number to know which
file to access. If the file is not opened, read_EXAM and write_EXAM will show the error message
“ERROR: Open the file first.”
• The read_EXAM and write_EXAM commands must not look for the file in the partition, instead
they use the data structures in the operating system that were initialized by open_EXAM.
• Once a cell has been used to open a file, that call cannot be used again. An error will be generated,
“ERROR: Index number in use.”, if the script attempts to open the same cell number.
• Apart from these points, the read_EXAM and write_EXAM commands will behave in the same
way as the given read and write commands.
Testing the code
Test your code with the following test file (also available in TESTFILE_PROB1.txt).
1. mount partition1 10 5
2. write_EXAM 0 [hello]
3. open_EXAM 0 file1
4. write_EXAM 0 [hello world test]
5. open_EXAM 0 file2
6. open_EXAM 1 file2
7. read_EXAM 0 var
8. print var
9. quit

The command on line 2 should display: ERROR: Open the file first.
The command on line 5 should display: ERROR: Index number in use.
The command on line 8 should display: hello world test

Notes:
• We will not test other corner cases. We will test your solution with the above test file and by
looking at your source code to see if it was constructed correctly and whether it respects the
expected programming style for this class.
• Your code will also be analyzed by MOSS for cheating.
• Your solution must run on mimi.
Marking breakdown:
• 1 point. Using provided code hooks and naming
• 3 points. Correct initialization OS data structures during open_EXAM.
• 2 points. Read_EXAM and write_EXAM commands syntax correctly uses file index.
• 3 points. TESTFILE_PROB1.txt runs to specification
• Your TA can remove up to 3 points from the total if the coding style is not respected.

Operating Systems COMP 310 – ECSE 427 McGill University
Vybihal & Balmau Final Exam Project Page 7 of 10
Problem 2: Close Command [10 points]

Change the provided codebase to add the close file command to your scripting language. The syntax of
your close command is:
close_EXAM
• The file_ID_in_active_file_table parameter is an integer that corresponds to the array
cell index in the active file table where the user has previously opened the file.
Code hooks in the codebase
You were provided with a function template in interpreter.c called closeCommandEXAM(). You
have also been provided with two empty files, DISK_driver_problem2.c (and .h). Use these three
places to implement the close_EXAM functionality. Feel free to expose other functions and data
structures already existent in the codebase to your DISK_driver_problem2 files. You should be able
to complete your implementation by only modifying these three locations. However, if you absolutely
need to make modifications elsewhere in the codebase, make a note in the README file, explaining why.
Implementation details
• The close_EXAM command will free memory of any buffers used during opening, reading,
writing to a file.
• It will also make available the cell of the active file table data structure you used for Problem 1
to be useable for other opened files.
• The open_EXAM command, if used again, can reuse a closed cell.
• The close_EXAM command will return an error when it is asked to close a cell that is not in
use: “ERROR: Index number not in use.”
Testing the code
Test your code with the following test file (also available in TESTFILE_PROB2.txt).
1. mount partition2 10 5
2. open_EXAM 0 file1
3. write_EXAM 0 [hello world test]
4. close_EXAM 0
5. close_EXAM 0
6. open_EXAM 0 file1
7. read_EXAM 0 var
8. close_EXAM 0
9. print var
10. quit
The command on line 5 should display: ERROR: Index number not in use.
The command on line 9 should display: hello world test


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Vybihal & Balmau Final Exam Project Page 8 of 10
Notes:
• We will not test other corner cases. We will test your solution with the above test file and by
looking at your source code to see if it was constructed correctly and whether it respects the
expected programming style for this class.
• Your code will also be analyzed by MOSS for cheating.
• Your solution must run on mimi.
Marking breakdown:
• 2 points. Correct reset of index.
• 2 points. Correct freeing of buffers.
• 2 points. Correct behavior when closing a location that was not open.
• 4 points. TESTFILE_PROB2.txt runs to specification
• Your TA can remove up to 3 points from the total if the coding style is not respected.
Operating Systems COMP 310 – ECSE 427 McGill University
Vybihal & Balmau Final Exam Project Page 9 of 10
Problem 3: Seek Command [10 points]

Change the provided codebase to add the seek command to your scripting language. The syntax of your
seek command is:
seek_EXAM
• The file_ID_in_active_file_table parameter is an integer that corresponds to the array
cell index in the active file table where the user has previously opened the file.
• The offset parameter is an integer that can be positive or negative. A positive value moves the
file pointer towards the end of the file. A negative value moves the file pointer towards the
beginning of the file. The offset is computed from the current position of the file pointer.
Code hooks in the codebase
You were provided with a function template in interpreter.c called seekCommandEXAM(). You
have also been provided with two empty files, DISK_driver_problem3.c (and .h). Use these three
places to implement the seek_EXAM functionality. Feel free to expose other functions and data
structures already existent in the codebase to your DISK_driver_problem3 files. You should be able
to complete your implementation by only modifying these three locations. However, if you absolutely
need to make modifications elsewhere in the codebase, make a note in the README file, explaining why.
Implementation details
• The seek_EXAM command moves the file pointer by offset, starting from its current position.
• It uses the index number in the active file table to identify which file pointer is being updated.
• seek_EXAM does not move the file pointer outside of the file.
• If seek_EXAM is used to move beyond the file ending, the OS will stop the pointer at the end of
the file. A message is displayed: “ERROR: Out of bounds. Stopped at end of file.”
• If the command is used to go before the file beginning, the OS will stop the pointer at the
beginning of the file. “ERROR: Out of bounds. Stopped at start of file.”
• Note that the read_EXAM and write_EXAM commands will start from the position in the file
where seek_EXAM moved the file pointer.

Testing the code
Test your code with the following test file (also available in TESTFILE_PROB3.txt).
1. mount partition3 10 5
2. open_EXAM 0 file1
3. write_EXAM 0 [hello world test]
4. close_EXAM 0
5. open_EXAM 0 file1
6. seek_EXAM 0 6
7. read_EXAM 0 var
8. close_EXAM 0
Operating Systems COMP 310 – ECSE 427 McGill University
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9. print var
10. open_EXAM 0 file1
11. seek_EXAM 0 100
12. seek_EXAM 0 -100
13. quit
The command on line 9 should display: world test
The command on line 11 should display: ERROR: Out of bounds. Stopped at end of file.
The command on line 12 should display: ERROR: Out of bounds. Stopped at start of file.

Notes:
• We will not test other corner cases. We will test your solution with the above test file and by
looking at your source code to see if it was constructed correctly and whether it respects the
expected programming style for this class.
• Your code will also be analyzed by MOSS for cheating.
• Your solution must run on mimi.
Marking breakdown:
• 2 points. Seek uses index correctly.
• 2 points. File pointer updated correctly.
• 2 points. File boundary respected.
• 4 points. TESTFILE_PROB3.txt runs to specification
• Your TA can remove up to 3 points from the total if the coding style is not respected.



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