You need to have a Linux system for this assignment, those who have other operating systems can use a Virtual Machine with Linux. In Task-1 and Task-2, you need to establish a communication channel between

Programming Assignment 1
(Use of System Calls)
CS962: Operating System Principles
2023-24 Q3
eMasters in Cyber Security
Department of Computer Science and Engineering
Indian Institute of Technology Kanpur Due Date: 07-02-2024 23:55
This programming assignment makes you acquainted with the working principle of system calls. You need to have a Linux system for this assignment, those who have other operating systems can use a Virtual Machine with Linux. In Task-1 and Task-2, you need to establish a communication channel between two processes to achieve different functionalities as described in each task. In Task-3, you need to implement a utility to find disk space used by a directory. Template codes for tasks are placed under the PA1 folder in —PA1/Task-1, PA1/Task-2, and PA1/Task-3 directories in PA1.zip. Please go through the README file to understand the code base structure and build process of the assignment.
Task 1: Lets Do Some Calculation !!!! Client-Server Calculator [30 Points]
In this task, you need to implement a client-server based calculator. The client can submit any number of queries (i.e. mathematical expressions) to the server. The server will evaluate the client’s queries one by one and send back the answer as a response.
In this task, the main process will call fork to create a child process where child process acts as the server and the parent (main process) acts as client. The server will respond to all queries submitted by the client until it receives a specific terminating word (mentioned below) as a query from the client. After receiving the specific terminating word, the server will close the communication channel and exits. You need to use pipe to establish a communication channel between client and server.

Figure 1: Workflow of client-server based calculator.
Figure 1 shows the workflow of this client-server based calculator using pipes. The client (parent) should read expression (or may be terminating word) from standard input device, and will display result received from the server on standard output device as shown in the figure.
Requirement specifications for this task are as follows:
1. Input expression is always space separated, i.e. blank space between operand and operator.
2. Input expression always starts with an operand.
3. Input expression can have at most 20 operands (i.e., it can have at most 19 operators).
4. Operands in input expression may be an integer or float/double number.
5. Input expression can contain any combination of these five operators viz. (i) Addition (+), (ii) Subtraction (–), (iii) Multiplication (*), (iv) Division (/), and modulo (%).
6. When server performs calculation, it needs to follow BODMAS rule where division, multiplication and modulo operators are at same precedence (say precedence-1) and addition and subtraction are at precedence-2. According to BODMAS, server should first perform precedence-1 operations followed by precedence-2 operations. Among same precedence operations, server should perform operation from left to right.
7. When client receives END word from STDIN, it should send a termination signal to the server to terminate it properly.
8. On receiving the result of mathematical expressions from the server, client should print -RESULT: – followed by result. As an example, if client receive 5 from the server, then it should display -RESULT: 5- on STDOUT.
Example of Input & Output:
[INPUT] 1 + 5 * 2 – 1 + 10
[OUTPUT] RESULT: 20
[INPUT] 5 + 1 – 2 * 5 + 10
[OUTPUT] RESULT: 6
[INPUT] END
Implementation
• Inside Task-1 folder, you will find four C files namely—(i) task1_calc.c, (ii) task1_calculate.c, (iii) task1_client.c, and (iv) task1_server.c.
• You need to establish the communication channel and invoke the client and server function at the appropriate location inside the main function available in task1_calc.c.
• The client and server functionality need to be implemented in files task1_client.c and task1_server.c, respectively.
• In task1_calculate.c file, implement the calculate function that the server will invoke whenever required.
• Run make task1 command from the root folder of this assignment to get binary file named task1_calc. Use this binary to test the functionality of your implementation.
You can use below mentioned APIs to implement this part of the assignment. Refer to man page of these APIs to know about their usage.

Figure 2: Flow of establishing chat communication between two user.
pipe write exit
close sprintf sscanf wait strtok read strcmp
Task 2: Lets Chit-Chat !!! Chat Between Two Users [30 points]
In this task, you need to implement chat communication between two users using pipe. The main process acts as the driver and creates two child processes to facilitate communication between them using pipes. Each child processes (i.e. user-1 and user-2) exec the same -user program- binary to start the conversation between them. User program reads the chat content which has to be communicated to the other user from the chat content file (provided) and writes the chat content received from other user to the store content file. Each line in chat content can be a maximum of 500 characters.
Figure 2 shows the workflow of this chat communication. One of the users will be the initiator based upon the first line (keyword: initiate) in the chat content file. The initiator user will start the chat by sending next line (actual message) after initiate keyword in the chat content file. Similar to the initiator, any user can be the terminator of chat communication. Terminator will have keyword: bye in the chat content file or there is no more content left for communication in the chat content file.
As part of this task, you need to implement both driver and user program. The driver is responsible for fork & exec the user programs and establishing the communication channels between them. The user program is responsible for reading the chat messages and writing the replies as mentioned above. The driver program should accept 4 command line arguments as follows.
./task2_driver user1_content user1_store user2_content user2_store
Implementation
• Navigate to the Task-2 folder of code base, there are two C files, task2_driver.c and task2_user.c, to implement the driver and user program, respectively.
• After implementation, run the make task2 command from the root folder of this assignment. You will get two binary files at the root folder, namely task2_driver and task2_user (inside Task-2 folder), corresponding to the driver and user programs.
• You need to exec task2_user inside the driver program two times to mimic two users.
• Use the task2_driver binary as mentioned above to test the correct functionality of your implementation.
• You will find two additional text files for testing purposes, namely— chat-1.txt and chat-2.txt, inside the Task-2 folder, which holds the sample chat contents for two users.
You can use below mentioned APIs to implement this part of the assignment. Refer to man page of these APIs to know about their usage.
pipe fopen strcmp exec
close perror exit strcpy
wait getline sscanf sprintf
read free strlen fclose
write fputs atoi
Task 3: Directory Space Usage [40 points]
In this question, you have to write a program (myDU.c) that finds the space used by a directory (including its files, sub-directories, files in sub-directories, sub-sub directories etc.). Let’s call this directory as the Root directory.
Syntax