Assignment 1: Linux system calls and API

Files

Lab materials

A Linux PC (or virtual machine). You can use a VirtualBox guest machine that can be downloaded from the course book's website www.os-book.com, or your own Linux machine, or one of the Linux machines in T002 (the same kernel as in the 10th Edition of the book).

Some of these programming assignments are described in chapter 2 and 3 in the course book.

Task 1

In your Linux system, write a simple program that copies a file to another. The file names should be provided as command-line arguments, the same way as the standard "cp" command works. (If you don't remember how to get the command-line arguments in C, you can look at this example: showargs.c.) Use the standard C stdio interface with the library functions fopen, getc, putc and fclose. Compile with gcc. (Possibly useful command: "gcc -Wall -Wextra -std=c11 -O3 my-c-cp.c -o my-c-cp") With the following Makefile you can just type "make my-c-cp": 
CC = gcc
CFLAGS += -Wall -Wextra -std=c11 -O3
Look at the manual page for the strace command, using the command "man strace". Use strace to see the system calls. Questions: Why don't you see the calls to fopen, getc, putc and fclose? Which system calls do you see? What do they do? Are there more calls than you would have expected?

Here is one way to create a file called "1G" with 1 gibibyte of random data: 

dd if=/dev/urandom of=1G bs=1M count=1024
Question: Why do you need such a large file?

Task 2

In the course "Datorteknik" you have already used the Linux API with the system calls open, read, write and close. Make a new version of your program above that uses the Linux API to copy a file. Compare the speeds of the two versions. Questions: What results do you get? Which are the times you have measured? Is the Linux API version faster or slower than the stdio version? Why?

Use the program flush-cache.c to empty OS buffers. Question: Why do you need to do that? When do you need to do that?

Task 3

Do the "simple shell" assignment from the book, but with my "skalman" skeleton program (skalman-skeleton.c), and implement execution of programs using the system calls fork, execvp and wait to create a new process, start a program (with command-line arguments), and wait for the new process to terminate.

Don't forget what you have learned in your introductory programming courses: Test your program to try to find the bugs! For example, can it handle simple commands such as the following:

Task 4 (optional, counts toward a higher grade than 3)

For the grade 4, do at least three of the optional tasks in assignment 1-3. You can hand in the mandatory tasks first, and the optional tasks later, if you have time.

Modify the "skalman" shell so you can send output to a file using the syntax "program > file", as in the normal shell, and also input from a file using the syntax "program < file".

Task 5 (optional, counts toward a higher grade than 3)

Compare stdio, read and mmap. Create a big file, for exampel like this: 
dd if=/dev/urandom of=1G bs=1M count=1024
Compare the time it takes to read the file and count the number of 'x' in it, using: getc, fread, read, mmap. You can use the timing code in the attached file timing-example.c.

A useful tip: read using a larger buffer, such as 1 megabyte.

Report

Write down and hand in a short summary (1-2 pages) of what you have done. Don't forget to answer the questions above. Mail (as a pdf) to the teacher. All source code for your programs must be attached. It is good if you can also demonstrate your results at one of the scheduled lab times.

Thomas Padron-McCarthy (thomas.padron-mccarthy@oru.se), 3 maj 2022