View source for Embedded-Linux-Device-Driver/C2/Loading-and-Unloading-a-Module/English


{| style="border-spacing:0;"
| style="border:1pt solid #000000;padding:0.176cm;"| Visual cue
| style="border:1pt solid #000000;padding:0.176cm;"| Narration 

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 1:

Welcome slide:
| style="border:1pt solid #000000;padding:0.176cm;"| Welcome to the spoken tutorial on '''Loading and Unloading a Module.'''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 2:

Learning objectives:
* '''insmod '''tool to load a '''module'''.
* '''rmmod '''tool to unload a '''module.''' 
* '''dmesg''' command.
* '''depmod, modprobe, objdump''' tools.

| style="border:1pt solid #000000;padding:0.176cm;"| In this tutorial, we will learn how to use,

* '''insmod '''tool to load a '''module'''.
* '''rmmod '''tool to unload a '''module.''' 
* '''dmesg''' command.
* '''depmod, modprobe, objdump''' tools.
|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 3:

System Requirements:

* '''VirtualBox 5.2'''
* '''Ubuntu Linux 18.04 LTS''' operating system.
* '''Linux kernel '''version''' 5.0.0-31 generic.'''
* '''gedit text editor.'''

| style="border:1pt solid #000000;padding:0.176cm;"| To record this tutorial, I am using,
* '''VirtualBox 5.2'''
* '''Ubuntu Linux 18.04 LTS''' operating system.
* '''Linux kernel '''version''' 5.0.0-31 generic'''
* '''gedit text editor.'''
|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 4:

Prerequisites:
| style="border:1pt solid #000000;padding:0.176cm;"| To follow this tutorial, you should be familiar with:

* '''C programming language '''and
* Basics of''' Linux kernel''' 

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Open the '''terminal'''

Type >> '''cd DeviceDriver'''
| style="border:1pt solid #000000;padding:0.176cm;"| Open the '''terminal''' by pressing '''ALT+Ctrl+T '''keys simultaneously.

Press the '''Enter''' key after every command.

Go to the folder where '''simple_module dot c''' is saved.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''make all'''

Press '''Enter'''
| style="border:1pt solid #000000;padding:0.176cm;"| Remember, we have used '''make clean command''' earlier.

To '''compile''' the''' module '''again, type '''make space all'''.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type '''sudo su '''

Press '''Enter'''

Enter the''' password '''

| style="border:1pt solid #000000;padding:0.176cm;"| Type '''sudo space su '''

Enter the '''password''' of the system.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| 
| style="border:1pt solid #000000;padding:0.176cm;"| Let us now load the '''module simple_module dot c'''. in the '''kernel''' using '''insmod''' tool.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type '''>> insmod simple_module.ko'''

Highlight '''insmod'''
| style="border:1pt solid #000000;padding:0.176cm;"| Type '''insmod space simple_module dot ko.'''

The''' insmod '''tool loads a''' module '''into the '''kernel.'''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >>''' clear'''
| style="border:1pt solid #000000;padding:0.176cm;"| Clear the screen.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type '''lsmod | head -5'''

Press''' Enter'''

Highlight '''lsmod '''

| style="border:1pt solid #000000;padding:0.176cm;"| Let us check whether a '''module''' is loaded into the''' kernel '''or not.

Type''' lsmod space pipe space head space hyphen 5.'''

We know '''lsmod command''' shows the list of '''modules '''loaded in the current '''kernel.'''

So this '''command '''displays the first five '''modules''' of the list.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''man pipe '''

Press '''Enter'''
| style="border:1pt solid #000000;padding:0.176cm;"| To know more about''' Linux command''' go through the '''man page '''as shown.

Type '''man space pipe '''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| 


Press''' q '''
| style="border:1pt solid #000000;padding:0.176cm;"| Here, you get more information about''' pipe command.'''

Likewise, explore the '''command head '''to know more.

Press ‘'''q'''’ to exit.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Show the '''output'''

Highlight '''simple_module'''

Highlight '''16384'''
| style="border:1pt solid #000000;padding:0.176cm;"| Here, you can see the name of the '''module''' in this list.

It shows '''memory''' utilised by this '''module'''.

It indicates that the '''module '''is loaded into the '''kernel '''successfully.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''clear'''

| style="border:1pt solid #000000;padding:0.176cm;"| Clear the screen.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''dmesg | grep my_module '''

Press '''Enter'''

Highlight '''dmesg'''

Highlight '''grep my_module'''

Highlight '''dmesg | grep my_module '''
| style="border:1pt solid #000000;padding:0.176cm;"| Type '''dmesg space pipe space grep space my_module.'''

It displays messages from '''kernel log buffer.'''

The''' grep command''' is used to search for lines matching a specified pattern.

It displays the messages containing the '''string my_module''' in the''' simple_module.c'''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''my_module :''' '''inside the init function of our module '''

| style="border:1pt solid #000000;padding:0.176cm;"| Here, '''dmesg '''prints the message from '''init function '''of a '''module.'''

As a '''module''' is loaded into the '''kernel''', only '''init function '''is executed.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''clear'''

| style="border:1pt solid #000000;padding:0.176cm;"| Clear the screen.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| 
| style="border:1pt solid #000000;padding:0.176cm;"| Now let us see how to unload a '''module '''from the '''kernel.'''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type''' rmmod simple_module.ko'''

Press '''Enter'''

Highlight '''rmmod '''
| style="border:1pt solid #000000;padding:0.176cm;"| Type '''rmmod space simple_module dot ko'''.

This tool unloads a '''module '''from the '''kernel'''.

Let us check this.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''lsmod | head -5 '''and press '''Enter'''

Show the output
| style="border:1pt solid #000000;padding:0.176cm;"| Type '''lsmod space pipe space head space hyphen 5.'''

Now, you can see the '''module '''name has disappeared from this list.

It indicates that the''' module''' is unloaded from the '''kernel '''successfully.
|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >>''' clear'''

| style="border:1pt solid #000000;padding:0.176cm;"| Clear the '''screen.'''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''dmesg | grep my_module'''

Press '''Enter.'''

Show the output

Highlight''' Inside the exit function of our module '''
| style="border:1pt solid #000000;padding:0.176cm;"| Let us see the '''printk '''messages of a '''module'''.

Type '''dmesg space pipe space grep space my_ module '''

Now, you can see the messages from '''exit function '''also.

As a '''module''' is unloaded from the '''kernel''', '''exit function '''is executed.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''clear'''

Press '''Enter'''
| style="border:1pt solid #000000;padding:0.176cm;"| Clear the screen.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| 
| style="border:1pt solid #000000;padding:0.176cm;"| Let us see the use of the '''depmod command.'''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''man 8 depmod'''

Press''' Enter'''

| style="border:1pt solid #000000;padding:0.176cm;"| for that, type '''man space 8 space depmod'''.

It creates a '''dependency''' file named '''modules.dep. '''

This '''dependency''' file is later used by '''modprobe''' tool.

You can get more information about '''depmod''' from it’s '''manpage.''' 

Press ‘'''q'''’ to exit.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| 
| style="border:1pt solid #000000;padding:0.176cm;"| Let us see the use of the '''modprobe''' tool.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''man 8 modprobe '''

Press''' Enter'''
| style="border:1pt solid #000000;padding:0.176cm;"| Type '''man space 8 space modprobe.'''

The''' modprobe''' tool intelligently adds or removes a '''module''' from the''' kernel.'''

Some '''modules '''depend on other '''modules'''.

This tool automatically loads and unloads its '''dependent modules.'''

You can get more information about '''modprobe''' tool from it’s '''manpage'''

The '''modprobe''' expects an up-to-date '''modules dot dep file '''generated by the''' depmod.'''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Press q
| style="border:1pt solid #000000;padding:0.176cm;"| Press ‘'''q'''’ to exit.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''clear'''

Press '''Enter'''
| style="border:1pt solid #000000;padding:0.176cm;"| Clear the screen.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''insmod simple_module.ko'''

Press '''Enter'''
| style="border:1pt solid #000000;padding:0.176cm;"| Let us now load a '''module''' in the '''kernel '''again.

Type '''insmod space simple_module dot ko '''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''lsmod | head -5'''

Press '''Enter'''
| style="border:1pt solid #000000;padding:0.176cm;"| Let us check a '''module''' is loaded into the '''kernel''' or not.

Type '''lsmod space pipe space head space hyphen 5 '''

As a '''module''' loaded into the '''kernel''' successfully, it appears here.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''clear'''

Press '''Enter'''.
| style="border:1pt solid #000000;padding:0.176cm;"| Clear the screen.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''readelf hyphen h simple_module.ko'''

Press '''Enter'''.

Highlight '''.ko'''

Highlight''' ELF Header.'''
| style="border:1pt solid #000000;padding:0.176cm;"| Let us see the '''ELF''' file of the '''module'''.

Type '''readelf space hyphen h space simple_module dot ko '''

Here, the''' dot ko''' is an '''ELF''' file. 

Each''' ELF''' file is made up of one '''ELF header''', followed by '''file''' data. 

The''' elf header''' describes the overall information of the '''module dot ko''' file.

'''ELF''' means “'''Executable and Linking Format'''”.

It is a standard '''executable file format '''in '''Linux'''.

Clear the screen.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''objdump -f simple_module.ko'''

Press '''Enter'''

Highlight '''-f'''

Highlight '''simple_module.ko'''

Highlight '''elf64-x86-64'''

Highlight '''i386:x86-64'''

Highlight '''start address'''
| style="border:1pt solid #000000;padding:0.176cm;"| Let us see the information about the '''object''' file

Type '''objdump space hyphen f space simple_module dot ko.'''

The''' hyphen f '''option shows our '''module’s elf header'''.

It shows the name of a '''module, '''the '''file '''format of a '''module file'''.

It shows the '''architecture''' of our system, and the entry point '''function’s address.'''

For more information, go through its '''manpage.'''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''clear '''

Press '''Enter'''
| style="border:1pt solid #000000;padding:0.176cm;"| Clear the screen.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''rmmod simple_module'''

Press '''Enter'''
| style="border:1pt solid #000000;padding:0.176cm;"| To unload the''' module''' from the '''kernel''', type '''rmmod simple_module.ko'''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''make clean'''

Press '''Enter'''
| style="border:1pt solid #000000;padding:0.176cm;"| Type '''make space clean.'''

So all extra files will be removed from the '''present working directory. '''
|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''exit'''

Press '''Enter'''

Type >> exit

Press '''Enter'''
| style="border:1pt solid #000000;padding:0.176cm;"| To go back to '''regular user''', type '''exit''' 

To go back to '''user login, type''' exit'''.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 5:

Summary:
| style="border:1pt solid #000000;padding:0.176cm;"| In this tutorial, we learnt how to use

* '''insmod '''tool to load a '''module'''.
* '''rmmod '''tool to unload a '''module.''' 
* '''dmesg command'''.
* '''depmod, modprobe, objdump''' tools.
|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 6:

Assignment:
| style="border:1pt solid #000000;padding:0.176cm;"| As an assignment,

# Open the '''simple_module.c '''file. 
# Change the message in '''printk function''' of '''init_function.'''
# Load the '''module''' using '''insmod''' tool.
# See the output of '''dmesg command'''.
# Remove the '''module''' using''' rmmod''' tool

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 7:


About Spoken Tutorial Project:
| style="border:1pt solid #000000;padding:0.176cm;"|
* The video at the following link summarizes the Spoken Tutorial project.

* Please download and watch it.
|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 8:

Spoken Tutorial workshops:
| style="border:1pt solid #000000;padding:0.176cm;"| The''' Spoken Tutorial Project''' Team conducts workshops and gives certificates.

For more details, please write to us.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 9:

Forum questions:
| style="border:1pt solid #000000;padding:0.176cm;"| Please post your timed queries in this forum.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 10:

Forum for specific questions:
| style="border:1pt solid #000000;padding:0.176cm;"|
* Do you have any general or technical questions on Embedded Linux Device Driver?
* Please visit the FOSSEE forum and post your question.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 11

Acknowledgment:
| style="border:1pt solid #000000;padding:0.176cm;"| Spoken Tutorial project is funded by MHRD, Government of India.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 12:

Thank you slide:
| style="border:1pt solid #000000;padding:0.176cm;"| This tutorial has been contributed by FOSSEE and Spoken Tutorial Project, IIT Bombay. 

This is Mayuri Panchakshari signing off.

Thanks for watching.

|}