Operating Systems 2017F: Tutorial 2 - Revision history

Akhil: /* Getting Started */

2017-09-27T04:27:01Z

Getting Started

← Older revision		Revision as of 04:27, 27 September 2017
Line 3:		Line 3:
	==Getting Started==		==Getting Started==

	You should download ~~and run~~ [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut2/3000shell.c 3000shell.c] on a Ubuntu Linux 16.04 system or similar. Compile it using the command		You should download [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut2/3000shell.c 3000shell.c] on a Ubuntu Linux 16.04 system or similar. Compile it using the command
	gcc -O -Wall 3000shell.c -o 3000shell		gcc -O -Wall 3000shell.c -o 3000shell
	In the labs, use either the 2401 Virtualbox VM or create your own in [openstack.scs.carleton.ca SCS Openstack] using the Ubuntu 16.04 cloud image. If you have issues with Openstack please ask the TAs for assistance.		In the labs, use either the 2401 Virtualbox VM or create your own in [openstack.scs.carleton.ca SCS Openstack] using the Ubuntu 16.04 cloud image. If you have issues with Openstack please ask the TAs for assistance.

Akhil: /* Tasks/Questions */

2017-09-27T04:26:18Z

Tasks/Questions

← Older revision		Revision as of 04:26, 27 September 2017
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	==Tasks/Questions==		==Tasks/Questions==
			# Compile and run 3000shell.c
	# Try running programs in the background using &. What happens to the input and output of the program? Try this for simple programs like ls and bc. Then, try it for more complex interactive programs such as nano and top.		# Try running programs in the background using &. What happens to the input and output of the program? Try this for simple programs like ls and bc. Then, try it for more complex interactive programs such as nano and top.
	# You may have trouble interacting with the shell after running programs in the background. How can you recover from such a situation?		# You may have trouble interacting with the shell after running programs in the background. How can you recover from such a situation?

Soma at 15:08, 25 September 2017

2017-09-25T15:08:09Z

← Older revision		Revision as of 15:08, 25 September 2017
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	~~'''THIS TUTORIAL IS NOT YET FINALIZED'''~~

	In this tutorial you will be experimenting with and extending [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut2/3000shell.c 3000shell.c] (listed below).		In this tutorial you will be experimenting with and extending [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut2/3000shell.c 3000shell.c] (listed below).

Soma: /* Tasks/Questions */

2017-09-25T03:06:52Z

Tasks/Questions

← Older revision		Revision as of 03:06, 25 September 2017
Line 21:		Line 21:
	# Implement output redirection for running external programs, i.e. "ls > ls.log".		# Implement output redirection for running external programs, i.e. "ls > ls.log".
	# Make plist output the parent process id for each process, e.g. "5123 ls (5122)". Pay attention to the stat and status files in the per-process directories in /proc.		# Make plist output the parent process id for each process, e.g. "5123 ls (5122)". Pay attention to the stat and status files in the per-process directories in /proc.
			# (Advanced) Implement I/O redirection for plist
			# (Advanced) Implement a built-in 300kill command that works like the standard kill command.

	==Code==		==Code==

Soma: /* Tasks/Questions */

2017-09-25T03:05:25Z

Tasks/Questions

← Older revision		Revision as of 03:05, 25 September 2017
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	# Try running programs in the background using &. What happens to the input and output of the program? Try this for simple programs like ls and bc. Then, try it for more complex interactive programs such as nano and top.		# Try running programs in the background using &. What happens to the input and output of the program? Try this for simple programs like ls and bc. Then, try it for more complex interactive programs such as nano and top.
	# You may have trouble interacting with the shell after running programs in the background. How can you recover from such a situation?		# You may have trouble interacting with the shell after running programs in the background. How can you recover from such a situation?
			# Why are lines 208-211 there (the check for pid == -1)?
			# Make find_binary show every attempt to find a binary.
			# Make the shell output "Ouch!" when you send it a SIGUSR1 signal.
			# Delete line 243 (SA_RESTART). How does the behavior of 3000shell change?
	# Replace the use of find_env() with getenv(). How do their interfaces differ?		# Replace the use of find_env() with getenv(). How do their interfaces differ?
	# Use putenv() to implement LASTCOMMAND from Tutorial 1.		# Use putenv() to implement LASTCOMMAND from Tutorial 1.
	# ~~Delete line 243 (SA_RESTART)~~. ~~How does the behavior of 3000shell change?~~		# Implement output redirection for running external programs, i.e. "ls > ls.log".
	# Make plist output the parent process id for each process, e.g. "5123 ls (5122)". Pay attention to the stat and status files in the per-process directories in /proc.		# Make plist output the parent process id for each process, e.g. "5123 ls (5122)". Pay attention to the stat and status files in the per-process directories in /proc.
	~~# Why are lines 208-211 there (the check for pid == -1)?~~
	~~# Make the shell output "Ouch!" when you send it a SIGUSR1 signal.~~
	~~# Make find_binary show every attempt to find a binary.~~
	~~# Implement output redirection for running external programs, i.e. "ls > ls.log".~~

	==Code==		==Code==

Soma at 03:03, 25 September 2017

2017-09-25T03:03:36Z

← Older revision		Revision as of 03:03, 25 September 2017
Line 21:		Line 21:
	# Make find_binary show every attempt to find a binary.		# Make find_binary show every attempt to find a binary.
	# Implement output redirection for running external programs, i.e. "ls > ls.log".		# Implement output redirection for running external programs, i.e. "ls > ls.log".

	~~==Tasks==~~


	==Code==		==Code==

Soma: /* Experiments */

2017-09-25T03:02:58Z

Experiments

← Older revision		Revision as of 03:02, 25 September 2017
Line 9:		Line 9:
	In the labs, use either the 2401 Virtualbox VM or create your own in [openstack.scs.carleton.ca SCS Openstack] using the Ubuntu 16.04 cloud image. If you have issues with Openstack please ask the TAs for assistance.		In the labs, use either the 2401 Virtualbox VM or create your own in [openstack.scs.carleton.ca SCS Openstack] using the Ubuntu 16.04 cloud image. If you have issues with Openstack please ask the TAs for assistance.

	==~~Experiments~~==		==Tasks/Questions==

	#		# Try running programs in the background using &. What happens to the input and output of the program? Try this for simple programs like ls and bc. Then, try it for more complex interactive programs such as nano and top.
			# You may have trouble interacting with the shell after running programs in the background. How can you recover from such a situation?
			# Replace the use of find_env() with getenv(). How do their interfaces differ?
			# Use putenv() to implement LASTCOMMAND from Tutorial 1.
			# Delete line 243 (SA_RESTART). How does the behavior of 3000shell change?
			# Make plist output the parent process id for each process, e.g. "5123 ls (5122)". Pay attention to the stat and status files in the per-process directories in /proc.
			# Why are lines 208-211 there (the check for pid == -1)?
			# Make the shell output "Ouch!" when you send it a SIGUSR1 signal.
			# Make find_binary show every attempt to find a binary.
			# Implement output redirection for running external programs, i.e. "ls > ls.log".

	==Tasks==		==Tasks==

Soma at 02:15, 25 September 2017

2017-09-25T02:15:47Z

← Older revision		Revision as of 02:15, 25 September 2017
Line 1:		Line 1:
			'''THIS TUTORIAL IS NOT YET FINALIZED'''

	In this tutorial you will be experimenting with and extending [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut2/3000shell.c 3000shell.c] (listed below).		In this tutorial you will be experimenting with and extending [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut2/3000shell.c 3000shell.c] (listed below).

Line 6:		Line 8:
	gcc -O -Wall 3000shell.c -o 3000shell		gcc -O -Wall 3000shell.c -o 3000shell
	In the labs, use either the 2401 Virtualbox VM or create your own in [openstack.scs.carleton.ca SCS Openstack] using the Ubuntu 16.04 cloud image. If you have issues with Openstack please ask the TAs for assistance.		In the labs, use either the 2401 Virtualbox VM or create your own in [openstack.scs.carleton.ca SCS Openstack] using the Ubuntu 16.04 cloud image. If you have issues with Openstack please ask the TAs for assistance.

			==Experiments==

			#

	==Tasks==		==Tasks==

Soma: /* Code */

2017-09-25T02:09:54Z

Code

← Older revision		Revision as of 02:09, 25 September 2017
Line 12:		Line 12:
	==Code==		==Code==

	<source lang="c" ~~lines~~>		<source lang="c" line>
	/* 3000shell.c */		/* 3000shell.c */
	/* v1 Sept. 24, 2017 */		/* v1 Sept. 24, 2017 */

Soma: Created page with "In this tutorial you will be experimenting with and extending [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut2/3000shell.c 3000shell.c] (listed below). ==Getting..."

2017-09-25T02:09:43Z

Created page with "In this tutorial you will be experimenting with and extending [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut2/3000shell.c 3000shell.c] (listed below). ==Getting..."

New page

In this tutorial you will be experimenting with and extending [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut2/3000shell.c 3000shell.c] (listed below).

==Getting Started==

You should download and run [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/tut2/3000shell.c 3000shell.c] on a Ubuntu Linux 16.04 system or similar. Compile it using the command
gcc -O -Wall 3000shell.c -o 3000shell
In the labs, use either the 2401 Virtualbox VM or create your own in [openstack.scs.carleton.ca SCS Openstack] using the Ubuntu 16.04 cloud image. If you have issues with Openstack please ask the TAs for assistance.

==Tasks==

==Code==

<source lang="c" lines>
/* 3000shell.c */
/* v1 Sept. 24, 2017 */
/* based off of csimpleshell.c, Enrico Franchi © 2005
https://web.archive.org/web/20170223203852/
http://rik0.altervista.org/snippets/csimpleshell.html */
/* Original under "BSD" license */
/* This version is under 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 <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <dirent.h>
#include <ctype.h>
#include <fcntl.h>
#include <signal.h>

#define BUFFER_SIZE 1<<16
#define ARR_SIZE 1<<16
#define COMM_SIZE 32

const char *proc_prefix = "/proc";

void parse_args(char *buffer, char** args,
size_t args_size, size_t *nargs)
{
char *buf_args[args_size]; /* You need C99 */
char **cp;
char *wbuf;
size_t i, j;

wbuf=buffer;
buf_args[0]=buffer;
args[0] =buffer;

for(cp=buf_args; (*cp=strsep(&wbuf, " \n\t")) != NULL ;){
if ((*cp != '\0') && (++cp >= &buf_args[args_size]))
break;
}

for (j=i=0; buf_args[i]!=NULL; i++){
if(strlen(buf_args[i])>0)
args[j++]=buf_args[i];
}

*nargs=j;
args[j]=NULL;
}

/* this is kind of like getenv() */
char *find_env(char *envvar, char *notfound, char *envp[])
{
const int MAXPATTERN = 128;
int i, p;
char c;
char pattern[MAXPATTERN];
char *value = NULL;

p = 0;
while ((c = envvar[p])) {
pattern[p] = c;
p++;
if (p == (MAXPATTERN - 2)) {
break;
}
}
pattern[p] = '=';
p++;
pattern[p] = '\0';

i = 0;
while (envp[i] != NULL) {
if (strncmp(pattern, envp[i], p) == 0) {
value = envp[i] + p;
}
i++;
}

if (value == NULL) {
return notfound;
} else {
return value;
}
}

void find_binary(char *name, char *path, char *fn, int fn_size) {
char *n, *p;
int r, stat_return;

struct stat file_status;

if (name[0] == '.' || name[0] == '/') {
strncpy(fn, name, fn_size);
return;
}

p = path;
while (*p != '\0') {
r = 0;
while (*p != '\0' && *p != ':' && r < fn_size - 1) {
fn[r] = *p;
r++;
p++;
}

fn[r] = '/';
r++;

n = name;
while (*n != '\0' && r < fn_size) {
fn[r] = *n;
n++;
r++;
}
fn[r] = '\0';

stat_return = stat(fn, &file_status);

if (stat_return == 0) {
return;
}

if (*p != '\0') {
p++;
}
}
}

void setup_comm_fn(char *pidstr, char *comm_fn)
{
char *c;

strcpy(comm_fn, proc_prefix);
c = comm_fn + strlen(comm_fn);
*c = '/';
c++;
strcpy(c, pidstr);
c = c + strlen(pidstr);
strcpy(c, "/comm");
}

void plist()
{
DIR *proc;
struct dirent *e;
int result;
char comm[COMM_SIZE]; /* seems to just need 16 */
char comm_fn[512];
int fd, i, n;

proc = opendir(proc_prefix);

if (proc == NULL) {
fprintf(stderr, "ERROR: Couldn't open /proc.\n");
}

for (e = readdir(proc); e != NULL; e = readdir(proc)) {
if (isdigit(e->d_name[0])) {
setup_comm_fn(e->d_name, comm_fn);
fd = open(comm_fn, O_RDONLY);
if (fd > -1) {
n = read(fd, comm, COMM_SIZE);
close(fd);
for (i=0; i < n; i++) {
if (comm[i] == '\n') {
comm[i] = '\0';
break;
}
}
printf("%s: %s\n", e->d_name, comm);
} else {
printf("%s\n", e->d_name);
}
}
}

result = closedir(proc);
if (result) {
fprintf(stderr, "ERROR: Couldn't close /proc.\n");
}
}

void signal_handler(int the_signal)
{
int pid, status;

if (the_signal == SIGHUP) {
fprintf(stderr, "Received SIGHUP.\n");
return;
}

if (the_signal != SIGCHLD) {
fprintf(stderr, "Child handler called for signal %d?!\n",
the_signal);
return;
}

pid = wait(&status);

if (pid == -1) {
/* nothing to wait for */
return;
}

if (WIFEXITED(status)) {
fprintf(stderr, "\nProcess %d exited with status %d.\n",
pid, WEXITSTATUS(status));
} else {
fprintf(stderr, "\nProcess %d aborted.\n", pid);
}
}

int main(int argc, char *argv[], char *envp[])
{
char buffer[BUFFER_SIZE];
char *args[ARR_SIZE];
char bin_fn[BUFFER_SIZE];
struct sigaction signal_handler_struct;
char *s;

int *ret_status = NULL;
size_t nargs;
pid_t pid;
int background;

char *username;
char *default_username = "UNKNOWN";

char *path;
char *default_path = "/usr/bin:/bin";

memset (&signal_handler_struct, 0, sizeof(signal_handler_struct));
signal_handler_struct.sa_handler = signal_handler;
signal_handler_struct.sa_flags = SA_RESTART;

if (sigaction(SIGCHLD, &signal_handler_struct, NULL)) {
fprintf(stderr, "Couldn't register SIGCHLD handler.\n");
}

if (sigaction(SIGHUP, &signal_handler_struct, NULL)) {
fprintf(stderr, "Couldn't register SIGHUP handler.\n");
}

username = find_env("USER", default_username, envp);
path = find_env("PATH", default_path, envp);

while(1){
printf("%s $ ", username);
s = fgets(buffer, BUFFER_SIZE, stdin);

if (s == NULL) {
/* we reached EOF */
printf("\n");
exit(0);
}

parse_args(buffer, args, ARR_SIZE, &nargs);

if (nargs==0) continue;

if (!strcmp(args[0], "exit")) {
exit(0);
}

if (!strcmp(args[0], "plist")) {
plist();
continue;
}

background = 0;
if (strcmp(args[nargs-1], "&") == 0) {
background = 1;
args[nargs-1] = NULL;
nargs--;
}

pid = fork();
if (pid) {
if (background) {
fprintf(stderr,
"Process %d running in the background.\n",
pid);
} else {
pid = wait(ret_status);
}
} else {
find_binary(args[0], path, bin_fn, BUFFER_SIZE);

if (execve(bin_fn, args, envp)) {
puts(strerror(errno));
exit(127);
}
}
}
return 0;
}
</source>