Operating Systems 2017F: Tutorial 5 - Revision history

Jagger: /* A simple kernel module */

2017-11-05T22:22:06Z

A simple kernel module

← Older revision		Revision as of 22:22, 5 November 2017
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	==A simple kernel module==		==A simple kernel module==

	# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-2015f/code/simple.zip this simple module], unpack, and build it by typing "make".		# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-2015f/code/simple.zip this simple module], unpack, and build it by typing "make". Use <code>wget</code>
	# Install the module using "sudo insmod simple.ko". The hello message is recorded in the kernel logs. How do you view the kernel logs?		# Install the module using "sudo insmod simple.ko". The hello message is recorded in the kernel logs. How do you view the kernel logs?
	# Check to see that the module has been loaded. How do you do this?		# Check to see that the module has been loaded. How do you do this?

Soma at 20:10, 5 November 2017

2017-11-05T20:10:10Z

← Older revision		Revision as of 20:10, 5 November 2017
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	In this tutorial you will be creating filesystems and installing kernel modules. It is '''highly recommended''' that you use a comp3000 openstack instance for the exercises below. In particular you may have difficulties compiling kernel modules on other systems. You will need root access to install kernel modules and mount filesystems.		In this tutorial you will be creating filesystems and installing kernel modules. It is '''highly recommended''' that you use a comp3000 openstack instance for the exercises below for two reasons. In particular you may have difficulties compiling kernel modules on other systems. You will need root access to install kernel modules and mount filesystems. These operations are potentially dangerous and mistakes could '''destroy all data''' on the Linux system. Consider yourself warned!

	==Filesystems==		==Filesystems==

Soma: /* Filesystems */

2017-11-05T20:08:08Z

Filesystems

← Older revision		Revision as of 20:08, 5 November 2017
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	# Run <tt>dumpe2fs foo</tt>. What does the output of this command mean?		# Run <tt>dumpe2fs foo</tt>. What does the output of this command mean?
	# What command do you run to check the filesystem in foo for errors?		# What command do you run to check the filesystem in foo for errors?
	# Run <tt>mount foo /mnt</tt>. How does this command change what files are accessible?		# Run <tt>sudo mount foo /mnt</tt>. How does this command change what files are accessible?
	# Run <tt>df</tt>. What device is mounted on /mnt? What is this device?		# Run <tt>df</tt>. What device is mounted on /mnt? What is this device?
	# Run <tt>rsync -a -v /etc /mnt</tt>. What does this command do? Explain the arguments as well.		# Run <tt>rsync -a -v /etc /mnt</tt>. What does this command do? Explain the arguments as well.
	# Run <tt>umount /mnt</tt>. What files can you still access, and what have gone away?		# Run <tt>sudo umount /mnt</tt>. What files can you still access, and what have gone away?
	# Run <tt>dd if=/dev/zero of=foo conv=notrunc count=10 bs=512</tt>. How does the "conv=notrunc" change dd's behavior (versus the command in question 1)?		# Run <tt>dd if=/dev/zero of=foo conv=notrunc count=10 bs=512</tt>. How does the "conv=notrunc" change dd's behavior (versus the command in question 1)?
	# Run <tt>sudo mount foo /mnt</tt>. What error do you get?		# Run <tt>sudo mount foo /mnt</tt>. What error do you get?

Soma: /* Filesystems */

2017-11-05T20:06:58Z

Filesystems

← Older revision		Revision as of 20:06, 5 November 2017
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	# Run <tt>ls -lai</tt> (by itself or for a specific directory). What are the numbers appearing in the left column?		# Run <tt>ls -lai</tt> (by itself or for a specific directory). What are the numbers appearing in the left column?
	# dd if=/dev/zero of=foo bs=8192 count=32K What is the logical size of the file? How much space does it consume on disk? (Hint: Look at the size option to ls.)		# dd if=/dev/zero of=foo bs=8192 count=32K What is the logical size of the file? How much space does it consume on disk? (Hint: Look at the size option to ls.)
	# Run <tt>mkfs.ext4 foo</tt>. (~~Say~~ "yes" to operating on a regular file.) Does foo consume any more space?		# Run <tt>mkfs.ext4 foo</tt>. (If asked, say "yes" to operating on a regular file.) Does foo consume any more space?
	# Run <tt>dumpe2fs foo</tt>. What does the output of this command mean?		# Run <tt>dumpe2fs foo</tt>. What does the output of this command mean?
	# What command do you run to check the filesystem in foo for errors?		# What command do you run to check the filesystem in foo for errors?

Soma: Created page with "In this tutorial you will be creating filesystems and installing kernel modules. It is '''highly recommended''' that you use a comp3000 openstack instance for the exercises b..."

2017-11-05T20:05:59Z

Created page with "In this tutorial you will be creating filesystems and installing kernel modules. It is '''highly recommended''' that you use a comp3000 openstack instance for the exercises b..."

New page

In this tutorial you will be creating filesystems and installing kernel modules. It is '''highly recommended''' that you use a comp3000 openstack instance for the exercises below. In particular you may have difficulties compiling kernel modules on other systems. You will need root access to install kernel modules and mount filesystems.

==Filesystems==

# Run <tt>ls -lai</tt> (by itself or for a specific directory). What are the numbers appearing in the left column?
# dd if=/dev/zero of=foo bs=8192 count=32K What is the logical size of the file? How much space does it consume on disk? (Hint: Look at the size option to ls.)
# Run <tt>mkfs.ext4 foo</tt>. (Say "yes" to operating on a regular file.) Does foo consume any more space?
# Run <tt>dumpe2fs foo</tt>. What does the output of this command mean?
# What command do you run to check the filesystem in foo for errors?
# Run <tt>mount foo /mnt</tt>. How does this command change what files are accessible?
# Run <tt>df</tt>. What device is mounted on /mnt? What is this device?
# Run <tt>rsync -a -v /etc /mnt</tt>. What does this command do? Explain the arguments as well.
# Run <tt>umount /mnt</tt>. What files can you still access, and what have gone away?
# Run <tt>dd if=/dev/zero of=foo conv=notrunc count=10 bs=512</tt>. How does the "conv=notrunc" change dd's behavior (versus the command in question 1)?
# Run <tt>sudo mount foo /mnt</tt>. What error do you get?
# What command can you run to make foo mountable again? What characteristic of the file system enables this command to work?
# Run the command <tt>truncate -s 1G bar</tt>. What is the logical size of bar, and how much space does it consume on disk? How does this compare with foo?
# How does the logical size of bar change when you create an ext4 filesystem in it? What about the space consumed on disk?

==A simple kernel module==

# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-2015f/code/simple.zip this simple module], unpack, and build it by typing "make".
# Install the module using "sudo insmod simple.ko". The hello message is recorded in the kernel logs. How do you view the kernel logs?
# Check to see that the module has been loaded. How do you do this?
# Remove the module from the kernel. What did you do?

==A character device kernel module==

# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-2015f/code/ones.zip ones], a kernel module implementing a character device that ouputs an unbounded string of "1"'s. Build, compile, and run it as before.
# What kernel messages does the module generate? Does it create any new files (other than /dev/ones)? If so, where?
# What happens when you "cat" the device /dev/ones? How can you limit the output?
# How can you modify your module to generate a kernel "Oops" as reported in the kernel logs or outright crash the kernel?

==Simple module==

===simple.c===

<source lang="c">
#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>

static int __init simple_init(void)
{
printk ("Hello kernel world!\n");
return 0;
}

static void __exit simple_exit(void)
{
printk ("Goodbye kernel world.\n");
return;
}

module_init(simple_init);
module_exit(simple_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Anil Somayaji <soma@scs.carleton.ca>");
MODULE_DESCRIPTION("A simple module");
</source>

===Makefile===

<source lang="make">
obj-m := simple.o
KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
default:
$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
</source>

==Ones module==

===ones.c===
<source lang="c">
/* Code derived from:
https://appusajeev.wordpress.com/2011/06/18/writing-a-linux-character-device-driver/
and
http://pete.akeo.ie/2011/08/writing-linux-device-driver-for-kernels.html
*/

#include <linux/module.h>
#include <linux/string.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <asm/uaccess.h>

#define dbg(format, arg...) do { if (debug) pr_info(CLASS_NAME ": %s: " format, __FUNCTION__, ## arg); } while (0)
#define err(format, arg...) pr_err(CLASS_NAME ": " format, ## arg)
#define info(format, arg...) pr_info(CLASS_NAME ": " format, ## arg)
#define warn(format, arg...) pr_warn(CLASS_NAME ": " format, ## arg)

#define DEVICE_NAME "ones"
#define CLASS_NAME "comp3000"

static struct class* ones_class = NULL;
static struct device* ones_device = NULL;
static int ones_major;

static int ones_open(struct inode *the_inode, struct file *f)
{
return 0;
}

static ssize_t ones_read(struct file *f, char *buf, size_t len, loff_t *offset)
{
size_t i;

for (i = 0; i < len; i++) {
put_user('1', buf++);
}

return i;
}

static int ones_release(struct inode *the_inode, struct file *f)
{
printk(KERN_ALERT "Ones device closed\n");
return 0;
}

static struct file_operations ones_fops = {
.open = ones_open,
.read = ones_read,
.release = ones_release,
};

static char *ones_devnode(struct device *dev, umode_t *mode)
{
if (mode)
*mode = 0444;
return NULL;
}

static int __init ones_init(void)
{
int retval;

ones_major = register_chrdev(0, DEVICE_NAME, &ones_fops);
if (ones_major < 0) {
err("failed to register device: error %d\n", ones_major);
retval = ones_major;
goto failed_chrdevreg;
}

ones_class = class_create(THIS_MODULE, CLASS_NAME);
if (IS_ERR(ones_class)) {
err("failed to register device class '%s'\n", CLASS_NAME);
retval = PTR_ERR(ones_class);
goto failed_classreg;
}

ones_class->devnode = ones_devnode;

ones_device = device_create(ones_class, NULL, MKDEV(ones_major, 0),
NULL, DEVICE_NAME);

if (IS_ERR(ones_device)) {
err("failed to create device '%s'\n", DEVICE_NAME);
retval = PTR_ERR(ones_device);
goto failed_devreg;
}

info("Ones device registered using major %d.\n", ones_major);

return 0;

failed_devreg:
class_unregister(ones_class);
class_destroy(ones_class);
failed_classreg:
unregister_chrdev(ones_major, DEVICE_NAME);
failed_chrdevreg:
return -1;
}

static void __exit ones_exit(void)
{
device_destroy(ones_class, MKDEV(ones_major, 0));
class_unregister(ones_class);
class_destroy(ones_class);
unregister_chrdev(ones_major, "ones");
info("Unloading Ones module.\n");
return;
}

module_init(ones_init);
module_exit(ones_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Anil Somayaji <soma@scs.carleton.ca>");
MODULE_DESCRIPTION("A write ones character device module");
</source>

===Makefile===
<source lang="make">
obj-m := ones.o
KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
default:
$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
</source>