Operating Systems 2019F Lecture 4 - Revision history

Soma at 21:54, 13 September 2019

2019-09-13T21:54:21Z

@@ Line 5: / Line 5: @@
 ==Topics==
 * files
 * open, read, write, close system calls
@@ Line 22: / Line 11: @@
 * programmatic directory access
 What can you do with a file normally?
 * open it <--- why?

Soma at 21:53, 13 September 2019

2019-09-13T21:53:01Z

← Older revision		Revision as of 21:53, 13 September 2019
Line 1:		Line 1:
	==Video==		==Video==

	Video from the lecture given on Sept. 11, 2019 [https://homeostasis.scs.carleton.ca/~soma/os-2019f/lectures/comp3000-2019f-~~lec03~~-~~20190911~~.m4v is now available].		Video from the lecture given on Sept. 13, 2019 [https://homeostasis.scs.carleton.ca/~soma/os-2019f/lectures/comp3000-2019f-lec04-20190913.m4v is now available].

	==Topics==		==Topics==

Soma: Created page with "==Video== Video from the lecture given on Sept. 11, 2019 [https://homeostasis.scs.carleton.ca/~soma/os-2019f/lectures/comp3000-2019f-lec03-20190911.m4v is now available]. ==..."

2019-09-13T21:52:45Z

Created page with "==Video== Video from the lecture given on Sept. 11, 2019 [https://homeostasis.scs.carleton.ca/~soma/os-2019f/lectures/comp3000-2019f-lec03-20190911.m4v is now available]. ==..."

New page

==Video==

Video from the lecture given on Sept. 11, 2019 [https://homeostasis.scs.carleton.ca/~soma/os-2019f/lectures/comp3000-2019f-lec03-20190911.m4v is now available].

==Topics==

* supervisor and user mode
* system calls
* process abstraction

==Notes==

<pre>
Lecture 4
---------

Topics
* files
* open, read, write, close system calls
* I/O redirection
* command line arguments
* programmatic directory access

What can you do with a file normally?
* open it <--- why?
* read from
* write to
* close it <--- why?

By having open and close, we tell the OS that
- we're going to do multiple operations on this file, and
- save the mapping of the filename to the underlying file data
- do permission checks now, not when we access the file

When you open a file, you get a file descriptor (a small int)
</pre>

==Code==

===filetest.c===
<source lang="c" line>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>

int main(int argc, char *argv[], char *envp)
{
int fd;
char *msg = "Hello world!\n";
char *stdmsg = "Hello standard out!\n";

write(1, stdmsg, 20);

/* open a file */

fd = open("test.txt", O_CREAT|O_APPEND|O_WRONLY,
S_IRUSR|S_IWUSR);

printf("Got file descriptor %d\n", fd);

/* write something to the file */
write(fd, msg, 13);

/* close the file */
close(fd);

return 0;
}
</source>

===dirtest.c===
<source lang="c" line>
#include <sys/types.h>
#include <dirent.h>
#include <stdio.h>

int main(int argc, char *argv[], char *envp[])
{
DIR *d;
struct dirent *entry;

if (argc > 1) {
d = opendir(argv[1]);
} else {
d = opendir(".");
}

entry = readdir(d);
while (entry) {
printf("Entry: %s\n", entry->d_name);
entry = readdir(d);
}

closedir(d);

return 0;
}
</source>