Operating Systems 2014F: Tutorial 7 - Revision history

Soma at 21:18, 13 November 2014

2014-11-13T21:18:31Z

← Older revision		Revision as of 21:18, 13 November 2014
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	~~'''This tutorial is not yet finalized.'''~~

	In this tutorial you will be learning about the basics of Linux kernel modules and character devices.		In this tutorial you will be learning about the basics of Linux kernel modules and character devices.

Soma: /* A character device module */

2014-11-13T04:26:00Z

A character device module

← Older revision		Revision as of 04:26, 13 November 2014
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	# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-2014f/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.		# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-2014f/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.
	# ~~Use mknod (with sudo) to make a character device "onesdev" that connects to~~ the ~~ones kernel~~ module~~. What command do you use~~? (~~Hint: the minor number doesn't matter.~~)		# 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? How can you limit the output?		# 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?		# How can you modify your module to generate a kernel "Oops" as reported in the kernel logs or outright crash the kernel?

Soma at 04:23, 13 November 2014

2014-11-13T04:23:48Z

← Older revision		Revision as of 04:23, 13 November 2014
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	MODULE_DESCRIPTION("A write ones character device module");		MODULE_DESCRIPTION("A write ones character device module");
	</source>		</source>


	===Makefile===		===Makefile===

Soma at 04:23, 13 November 2014

2014-11-13T04:23:35Z

← Older revision		Revision as of 04:23, 13 November 2014
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	</source>		</source>

	==Makefile==		===Makefile===
	<source lang="make">		<source lang="make">
	obj-m := ones.o		obj-m := ones.o

Soma: /* Ones module */

2014-11-13T04:23:11Z

Ones module

← Older revision		Revision as of 04:23, 13 November 2014
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	===ones.c===		===ones.c===
	<source lang="c">		<source lang="c">
	/* Code derived from https://appusajeev.wordpress.com/2011/06/18/writing-a-linux-character-device-driver/ */		/* 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/module.h>
	#include <linux/string.h>		#include <linux/string.h>
	#include <linux/fs.h>		#include <linux/fs.h>
			#include <linux/device.h>
	#include <linux/init.h>		#include <linux/init.h>
	#include <linux/kernel.h>		#include <linux/kernel.h>
	#include <asm/uaccess.h>		#include <asm/uaccess.h>

	static int ~~major~~;		#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)		static int ones_open(struct inode the_inode, struct file f)
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	.release = ones_release,		.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)		static int __init ones_init(void)
	{		{
	~~major~~ = register_chrdev(0, "~~ones~~", ~~&ones_fops~~);		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 (~~major<0~~) {		if (IS_ERR(ones_device)) {
	~~printk~~(~~KERN_ALERT~~ "~~Ones~~ device ~~registration failed.~~\n");		err("failed to create device '%s'\n", DEVICE_NAME);
	~~return major;~~		retval = PTR_ERR(ones_device);
	~~} else {~~		goto failed_devreg;
	~~printk~~(~~KERN_ALERT "Ones device registered using major %d.\n",~~
	~~major~~);
	~~return 0~~;
	}		}

			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)		static void __exit ones_exit(void)
	{		{
	unregister_chrdev(~~major~~, "ones");		device_destroy(ones_class, MKDEV(ones_major, 0));
	~~printk~~(~~KERN_ALERT~~ "Unloading Ones module.\n");		class_unregister(ones_class);
			class_destroy(ones_class);
			unregister_chrdev(ones_major, "ones");
			info("Unloading Ones module.\n");
	return;		return;
	}		}
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	MODULE_DESCRIPTION("A write ones character device module");		MODULE_DESCRIPTION("A write ones character device module");
	</source>		</source>


	==Makefile==		==Makefile==

Soma at 19:38, 12 November 2014

2014-11-12T19:38:08Z

← Older revision		Revision as of 19:38, 12 November 2014
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	===Building and running your first module===		===Building and running your first module===

	# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-~~2014w~~/code/simple.zip this simple module], unpack, and build it by typing "make".		# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-2014f/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?		# 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?
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	===A character device module===		===A character device module===

	# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-~~2014w~~/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.		# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-2014f/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.
	# Use mknod (with sudo) to make a character device "onesdev" that connects to the ones kernel module. What command do you use? (Hint: the minor number doesn't matter.)		# Use mknod (with sudo) to make a character device "onesdev" that connects to the ones kernel module. What command do you use? (Hint: the minor number doesn't matter.)
	# What happens when you "cat" the device? How can you limit the output?		# What happens when you "cat" the device? How can you limit the output?

Soma: /* A character device module */

2014-11-11T21:51:05Z

A character device module

← Older revision		Revision as of 21:51, 11 November 2014
Line 20:		Line 20:
	===A character device module===		===A character device module===

	# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-2014w/code ones], a kernel module implementing a character device that ouputs an unbounded string of "1"'s. Build, compile, and run it as before.		# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-2014w/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.
	# Use mknod (with sudo) to make a character device "onesdev" that connects to the ones kernel module. What command do you use? (Hint: the minor number doesn't matter.)		# Use mknod (with sudo) to make a character device "onesdev" that connects to the ones kernel module. What command do you use? (Hint: the minor number doesn't matter.)
	# What happens when you "cat" the device? How can you limit the output?		# What happens when you "cat" the device? 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?		# 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 module==

Soma: /* Building and running your first module */

2014-11-11T21:50:57Z

Building and running your first module

← Older revision		Revision as of 21:50, 11 November 2014
Line 5:		Line 5:
	===Building and running your first module===		===Building and running your first module===

	# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-2014w/code/ this simple module], unpack, and build it by typing "make".		# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-2014w/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?		# 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 21:29, 11 November 2014

2014-11-11T21:29:51Z

← Older revision		Revision as of 21:29, 11 November 2014
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	# When you type commands in a terminal window, you are interacting with a "pseudo tty" character device. Specifically, what device file(s) are being used by the terminal window, and what are the permissions and special file attributes (major, minor numbers) of these files? Are the permissions important?		# When you type commands in a terminal window, you are interacting with a "pseudo tty" character device. Specifically, what device file(s) are being used by the terminal window, and what are the permissions and special file attributes (major, minor numbers) of these files? Are the permissions important?

	==A character device module==		===A character device module===

	# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-2014w/code ones], a kernel module implementing a character device that ouputs an unbounded string of "1"'s. Build, compile, and run it as before.		# Download the source for [http://homeostasis.scs.carleton.ca/~soma/os-2014w/code ones], a kernel module implementing a character device that ouputs an unbounded string of "1"'s. Build, compile, and run it as before.

Soma at 21:29, 11 November 2014

2014-11-11T21:29:38Z

@@ Line 1: / Line 1: @@
 In this tutorial you will be learning about the basics of Linux kernel modules and character devices.
@@ Line 15: / Line 17: @@
 # What block device is used for the root filesystem on your system (the class VM or other Linux system)?
 # When you type commands in a terminal window, you are interacting with a "pseudo tty" character device.  Specifically, what device file(s) are being used by the terminal window, and what are the permissions and special file attributes (major, minor numbers) of these files?  Are the permissions important?
 ==Simple module==