Soma: Created page with "In this tutorial you will be experimenting with and extending [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut3/3000test.c 3000test.c] (listed below). ==Tasks/Ques..."

2019-01-21T20:02:30Z

Created page with "In this tutorial you will be experimenting with and extending [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut3/3000test.c 3000test.c] (listed below). ==Tasks/Ques..."

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In this tutorial you will be experimenting with and extending [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut3/3000test.c 3000test.c] (listed below).

==Tasks/Questions==

# Compile and run [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut3/3000test.c 3000test.c]. It takes a filename as an argument and reports information on the file. Try giving it the following and see what it reports:
#* a regular text file that exists
#* a directory
#* a symbolic link
#* a device file
# Change 3000test to use lstat rather than stat. How does its behavior change?
# Modify 3000test so when it is given a symbolic link it reports the name of the target. Use readlink(2).
# Are there files or directories that you cannot run 3000test on? Can you configure file/directory permissions so as to make something inaccessible to 3000test?
# How does the memory use of 3000test change as it runs? You may want to add calls to sleep(3) so you can observe its memory usage. You can create a 1 GB file of random data with the command <tt>dd if=/dev/urandom of=test bs=1024 count=1000000</tt>.
# Create a program 3000compare.c based on 3000test that compares the contents of two files and says whether or not they differ.
#* If given symbolic links it should report on where they point and only say they are equal if they refer to the same file.
#* If given two device files, it should say that they are equal if they are both the same kind of device file and have the same major and minor numbers.
#* If given two hard links to the same file, it should say that the files are identical because they refer to the same inode.
#* Other kinds of files (directories, pipes) should not be compared. Instead, it should report on the type of each file.

==Code==

<source lang="c" line>
/* 3000test.c */
/* v1 Oct. 1, 2017 */
/* Licenced under the GPLv3, copyright Anil Somayaji */
/* You really shouldn't be incorporating parts of this in any other code,
it is meant for teaching, not production */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>

void report_error(char *error)
{
fprintf(stderr, "Error: %s\n", error);

exit(-1);
}

int main(int argc, char *argv[])
{
struct stat statbuf;
char *fn;
int fd;
size_t len, i, count;

char *data;

if (argc < 2) {
if (argc < 1) {
report_error("no command line");
fprintf(stderr, "Usage: %s <file>\n", argv[0]);
} else {
report_error("Not enough arguments");
fprintf(stderr, "Usage: %s <file>\n", argv[0]);
}
}

fn = argv[1];

if (stat(fn, &statbuf)) {
report_error(strerror(errno));
}

len = statbuf.st_size;
printf("File %s: \n", fn);
printf(" inode %ld\n", statbuf.st_ino);
printf(" length %ld\n", len);

if (S_ISREG(statbuf.st_mode)) {
fd = open(fn, O_RDONLY);
if (fd == -1) {
report_error(strerror(errno));
}
data = (char *) mmap(NULL, len,
PROT_READ, MAP_SHARED, fd, 0);
if (data == MAP_FAILED) {
report_error(strerror(errno));
}

count = 0;
for (i=0; i<len; i++) {
if (data[i] == 'a') {
count++;
}
}

printf(" a count %ld\n", count);

if (munmap(data, len) == -1) {
report_error(strerror(errno));
}
close(fd);
}

return 0;
}
</source>

Operating Systems 2019W: Tutorial 3 - Revision history

Soma: Created page with "In this tutorial you will be experimenting with and extending [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut3/3000test.c 3000test.c] (listed below). ==Tasks/Ques..."