Final Test: Operating Systems

The grade formula is as follows:

Grade = 0.4 * Theory + 0.6 * Programming

Part 1. Theoretical Questions

Answer the theoretical questions in a few sentences (1-2 paragraphs for a question).

Use your own words. Copy-paste from external sources and other students will result in 100% penalty.

1. Memory management.
   • Memory layout of a program: What memory segments do you know? What purposes do they serve?
   • What ways to allocate memory do you know?
   • How dynamic memory allocation via malloc/free is implemented (using what data structures)?
   • Give definitions of payload, fragmentation, and placement strategies.
   • What is the purpose of the sbrk system call?
2. Processes.
   • What is a process? What parts does it contains (its layout in memory)?
   • List the states of a process and describe how it changes states.
   • What is Process Control Block (PCB)? What information does it contain?
   • Describe the idea of process creation with system calls fork and exec. What is the role of system call wait?
   • How to see the list of running processes in Linux (what system utilities do you know)?
3. Permissions.
   • What access rights do you know? What permission groups do you know?
   • How to view and how to change file permissions (what utility tools to use)?
   • Explain the setuid/setguid and sticky bit permissions.
   • Study the text below. What can you say about file1, file2, file3, and file4?

   acos@acos-vm:~/folder$ ls -li
   total 12
   892954 drwxr-x--- 2 acos   acos 4096 июн 16 14:53 file1
   795083 lrwxrwxrwx 1 acos   acos    5 июн 16 14:55 file2 -> file1
   792657 -rwsrwxr-x 2 myuser acos    7 июн 16 14:56 file3
   792657 -rwsrwxr-x 2 myuser acos    7 июн 16 14:56 file4
   

Part 2. Programming Task

Write a program in C that does the following:

• Calculates the value of the specified function f(x) in the range from argv[1] to argv[2] with step argv[3].
• Writes pairs x, f(x) into text file output.csv (CSV format).
• The function to be calculated has the following format:

  f(x) = f0(f1(x), f2(x), f3(x), f4(x))
  

  , where:

  • x is the function argument;
  • f0-f4 are functions that are individual according to the variant.

Example of Function (you need your variant, see below)

Note: the ^ symbol means “power”.

f0(a, b, c, d) = (a - b + c - d) / 2
f1(x) = 2*x^3 - 4*x^2 + 3*x + 1
f2(x) = sin(5*x)*4 + 3
f3(x) = 1 / (1 + e^(-7*x))
f4(x) = 2^x + 5

Requirements and Grades

• 4 Points: make all calculations and write to file in a parent process;
• + 2 Points: make all calculations and write to file in a child process (use fork);
• + 2 Points: execute the f0 function for the entire value range in a child process and send the resulting values to the parent process using a pipe;
• + 2 Points: create a thread for performing calculations and writing (sending to pipe) the results.

Hints

• Function f0 have the following structure:

  double f0(double a, double b, double c, double d) {
      return <math expr>;
  }
  

• Functions f1-f4 have the following structure:

  double f1(double x) {
      return <math expr>;
  }
  

• Command-line arguments (strings) can be converted to double using the atof function.
• Mathematical functions (such as sin, cos, pow, exp etc.) and constants (M_E) are in the math.h library. The program must be linked with the library: use the -lm GCC flag.
• To write to a file, open the file and redirect the standard output (STDOUT_FILENO) to this file with the dup2 system call. When you do this, you will be able to use printf to print to the file. If you do this in the parent process, redirection will work in both processes (parent and child).
• Sending data from child to parent using a pipe: see example in the manual.
  • Child: f(x) is calculated for a range of values and results (x and f(x)) are written (write(pfd[1], &x, sizeof(x))) to the pipe;
  • Parent: results (x and f(x)) are read (read(pfd[0], &x, sizeof(x))) from the pipe in a loop and printed.
• Threads are created and managed using functions pthread_create and pthread_join. Do not forget to link the pthread library using the GCC flag: -lpthread.
• To pass multiple values to a thread function (void * threadFunc(void *arg)), use a structure. For example:

  struct thread_args {
      int fd;
      double from;
      double to;
      double step;
  };
  

Variants

Choose your variant number according to your number in your group. See the lists of students here.

Variants for groups:

• Group 201
• Group 202
• Group 203
• Group 204