Difference between revisions of "Embedded-Linux-Device-Driver/C2/Simple-Loadable-Module/English"

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Line 32: Line 32:
 
* '''Ubuntu Linux 18.04 LTS''' operating system.
 
* '''Ubuntu Linux 18.04 LTS''' operating system.
 
* '''Linux kernel '''version''' 5.0.0-31 generic.'''
 
* '''Linux kernel '''version''' 5.0.0-31 generic.'''
−
* '''gedit '''Text''' '''Editor.
+
* '''gedit Text Editor'''.
 
| style="border:1pt solid #000000;padding:0.176cm;"| To record this tutorial, I am using,
 
| style="border:1pt solid #000000;padding:0.176cm;"| To record this tutorial, I am using,
  
Line 38: Line 38:
 
* '''Ubuntu Linux 18.04 LTS''' operating system.
 
* '''Ubuntu Linux 18.04 LTS''' operating system.
 
* '''Linux kernel '''version''' 5.0.0-31 generic '''
 
* '''Linux kernel '''version''' 5.0.0-31 generic '''
−
* '''gedit '''Text''' '''Editor.
+
* '''gedit Text Editor'''.
  
 
|-
 
|-
Line 65: Line 65:
 
* If not, to do the installation, follow the instructions in '''gedit''' series on this [http://spoken-tutorial.org/ https://spoken-tutorial.org]  
 
* If not, to do the installation, follow the instructions in '''gedit''' series on this [http://spoken-tutorial.org/ https://spoken-tutorial.org]  
  
−
| style="border:1pt solid #000000;padding:0.176cm;"| * To proceed further, make sure that '''Gedit''' is installed on your system.
+
| style="border:1pt solid #000000;padding:0.176cm;"|  
−
* If not, to do the installation, follow the instructions in '''gedit''' series on this website.
+
* To proceed further, make sure that '''Gedit''' is installed on your system.
 +
* If not, to do the installation, follow the instructions in '''Gedit''' series on this website.
  
 
|-
 
|-
Line 72: Line 73:
  
 
What is a''' kernel module'''?
 
What is a''' kernel module'''?
−
| style="border:1pt solid #000000;padding:0.176cm;"| * Code that is added to the''' kernel '''at runtime is called a '''module.'''
+
| style="border:1pt solid #000000;padding:0.176cm;"|  
−
* It extends the functionality of the '''kernel '''without the need to reboot the system.
+
* Code that is added to the''' kernel '''at '''runtime''' is called a '''module.'''
 +
* It extends the '''functionality''' of the '''kernel '''without the need to '''reboot''' the '''system'''.
  
−
* It communicates with the base '''kernel''' to complete their functions.  
+
* It communicates with the '''base kernel''' to complete their '''functions'''.  
  
 
|-
 
|-
Line 90: Line 92:
 
Code file - sample_module.c
 
Code file - sample_module.c
  
−
| style="border:1pt solid #000000;padding:0.176cm;"| Please download '''simple_module dot c''' from the code files link of this tutorial.
+
| style="border:1pt solid #000000;padding:0.176cm;"| Please download '''simple_module dot c''' from the '''Code files''' link of this tutorial.
 +
 
 
Make use of this file while practising.
 
Make use of this file while practising.
  
−
Remember the file path.
+
Remember the '''file path'''.
  
 
|-
 
|-
Line 101: Line 104:
 
| style="border:1pt solid #000000;padding:0.176cm;"| Let us open this '''file.'''
 
| style="border:1pt solid #000000;padding:0.176cm;"| Let us open this '''file.'''
  
−
Open the''' terminal''' by pressing '''Ctrl+Alt+T'''
+
Open the''' terminal''' by pressing '''Ctrl+Alt+T''' keys simultaneously.
  
−
keys simultaneously.
+
Press the '''Enter''' key after every '''command'''.
−
 
+
−
Press the '''Enter''' key after every command.
+
  
 
Go to the folder where '''simple_module dot c''' is saved.
 
Go to the folder where '''simple_module dot c''' is saved.
Line 117: Line 118:
 
|-
 
|-
 
| style="border:1pt solid #000000;padding:0.176cm;"| Show the '''program'''
 
| style="border:1pt solid #000000;padding:0.176cm;"| Show the '''program'''
 +
 +
  
 
Highlight'''<nowiki> <linux/init.h> </nowiki>'''
 
Highlight'''<nowiki> <linux/init.h> </nowiki>'''
 +
  
 
Highlight'''<nowiki> <linux/module.h></nowiki>'''
 
Highlight'''<nowiki> <linux/module.h></nowiki>'''
 +
  
 
Highlight'''<nowiki> <linux/kernel.h></nowiki>'''
 
Highlight'''<nowiki> <linux/kernel.h></nowiki>'''
 +
 
| style="border:1pt solid #000000;padding:0.176cm;"| At the start of the '''program''', there are some '''header files'''.
 
| style="border:1pt solid #000000;padding:0.176cm;"| At the start of the '''program''', there are some '''header files'''.
  
Line 129: Line 135:
 
The''' module dot h file''' contains '''functions '''related to the '''modules'''.
 
The''' module dot h file''' contains '''functions '''related to the '''modules'''.
  
−
The''' kernel dot h file''' contains functions such as '''printk.'''
+
The''' kernel dot h file''' contains '''functions''' such as '''printk.'''
  
 
|-
 
|-
Line 139: Line 145:
 
'''GPL''' means '''GNU Public License.'''
 
'''GPL''' means '''GNU Public License.'''
  
−
It is otherwise called as '''GNU, '''which''' '''is a free and open-source license'''.'''
+
It is otherwise called as '''GNU, '''which is a free and open-source license.
  
 
|-
 
|-
Line 148: Line 154:
 
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''MODULE_DESCRIPTION'''
 
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''MODULE_DESCRIPTION'''
  
−
| style="border:1pt solid #000000;padding:0.176cm;"| You can simply describe your '''module '''using this macro .
+
| style="border:1pt solid #000000;padding:0.176cm;"| You can simply describe your '''module '''using this '''macro'''.
 +
 
 +
I have given the description as “'''First Linux kernel module”.'''
 +
 
 +
|- .
 +
 
 +
I have given the description as “'''First Linux kernel module”.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''static int init_func(void)'''
 +
 
 +
Highlight '''return(0)'''
 +
 
 +
Highlight '''module_init()'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''init function '''will execute when a '''module '''is loaded into the '''kernel'''.
 +
 
 +
So it is called as an '''initialization''' '''function''' of a '''module'''.
 +
 
 +
If this '''function''' fails then the '''error '''will be '''returned'''.
 +
 
 +
It will '''return''' 0 to the '''kernel''' on successful '''execution'''.
 +
 
 +
'''Initialization function''' prints a simple message and '''returns''' zero.
 +
 
 +
The '''module init macro''' is used to register the '''init function.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' void exit_func (void)'''
 +
 
 +
Highlight '''module_exit()'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' exit function '''will execute when the '''module '''is unloaded from the '''kernel'''.
 +
 
 +
It is mostly used to cleanup the '''resources''' acquired by the '''module'''
 +
 
 +
The''' exit function''' will undo whatever the''' init function '''did.
 +
 
 +
The '''module underscore exit macro''' is used to register the '''exit function. '''
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''printk'''
 +
 
 +
Highlight '''KERN_INFO'''
 +
 
 +
Press >> '''Ctrl + S'''
 +
 
 +
Press '''Enter'''
 +
 
 +
Click on '''close''' option.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| In '''kernel '''programming, '''printk '''is used as a '''printing function.'''
 +
 
 +
It is similar to '''printf function '''in '''C programming'''.
 +
 
 +
Using this '''function, string data''' will get loaded in the '''kernel log buffer'''.
 +
 
 +
'''printk''' has an optional '''prefix string, Loglevel '''such as''' KERN_INFO.'''
 +
 
 +
'''Loglevel '''specifies the type of message being sent to the '''kernel message log'''.
 +
 
 +
'''KERN underscore INFO''' is used for informational messages.
 +
 
 +
For more '''log levels''', go through the '''Additional reading material''' link of this tutorial.
 +
 
 +
Press '''Ctrl + S''' keys to save the '''program '''.
 +
 
 +
Close the '''file.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"|
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Let us '''compile''' the code.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''gedit Makefile'''
 +
 
 +
Highlight the makefile
 +
 
 +
Press '''Enter'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| For that, we have to create a''' Makefile.'''
 +
 
 +
Type '''gedit Makefile '''
 +
 
 +
The '''Makefile''' is a special file containing '''shell commands'''.
 +
 
 +
Press '''Enter.'''
 +
 
 +
Create a '''Makefile '''where you have saved the '''simple_module dot c .'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Copy paste the makefile content
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type the '''code '''as shown.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''obj-m'''
 +
 
 +
Highlight '''simple_module.o'''
 +
 
 +
Highlight '''all:'''
 +
 
 +
Highlight '''clean:'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' obj hyphen m variable''' tells the '''kernel Makefile '''that this '''module '''needs to be '''compiled'''.
 +
 
 +
When you '''run''' the '''make all command''', then '''commands''' under '''all''' section will be '''executed'''.
 +
 
 +
If you '''run''' the '''make clean command''', it executes '''commands''' under the '''clean '''section.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''-C'''
 +
 
 +
Highlight '''uname -r'''
 +
Highlight''' (PWD)'''
 +
Highlight '''M=$(PWD)'''
 +
Highlight''' modules'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Using '''hyphen C''', we are '''running make command''' inside the''' kernel source directory.'''
 +
 
 +
As you know,''' uname hyphen r''' finds the current '''Linux kernel''' version of a '''system.'''
 +
 
 +
'''PWD '''means the '''present working directory.'''
 +
 
 +
This option tells the '''kernel makefile''' that the '''source code '''for the '''driver''' is in '''PWD'''.
 +
 
 +
The word '''modules''' tell the '''kernel makefile''' to build the '''modules'''.
 +
 
 +
But it will not '''build''' the complete '''kernel source code.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''clean'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The word '''clean''' tells the '''kernel makefile''' to clean the generated '''object files.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Press >> '''Ctrl + S'''
 +
 
 +
Click on the '''close'''.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Save the '''file''' and close the '''editor'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Open the '''terminal'''
 +
 
 +
Type >> '''make all'''
 +
 
 +
Press '''Enter'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
 
 +
Let us '''compile''' the '''program'''.
 +
 
 +
Type '''make space all.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type''' ls '''and press''' Enter'''
 +
 
 +
Highlight''' ls '''
 +
 
 +
Show the output
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Now type '''ls.'''
 +
 
 +
This '''command''' lists the '''files''' in the current '''directory.'''
 +
 
 +
Here, you can see the number of '''files''' created in this '''directory'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' module.symvers'''
 +
 
 +
Highlight''' mod.c '''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''module.symvers''' file contains a list of all '''symbols'''
 +
 
 +
These '''symbols '''are exported from the '''kernel build'''.
 +
 
 +
The '''mod.c file '''contains information about the '''module'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' mod.o'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| '''Mod.o''' file is '''object file''' resulting from the '''compilation''' of the '''mod.c file.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' .o'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This '''object file''' is created from the '''compilation''' of the '''module source file'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' modules.order'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| It will list out the order in which the compilation and creation of the '''.ko file''' takes place.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' .ko'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This is the final '''kernel module binary''' that is loaded into the '''kernel.'''
 +
 
 +
|-
 +
| 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 '''>> modinfo simple_module.ko'''
 +
 
 +
Press '''Enter'''
 +
 
 +
Highlight '''modinfo'''
 +
 
 +
Highlight '''filename'''
 +
 
 +
Highlight '''description'''
 +
 
 +
Highlight '''author, license'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Let us see the details of a '''module'''.
 +
 
 +
Type''' modinfo space simple_module dot ko.'''
 +
 
 +
This '''command''' displays information about the '''Linux kernel module. '''
 +
 
 +
The '''filename''' field contains an '''absolute path''' to the '''.ko kernel object file.'''
 +
 
 +
This field displays a short description of a '''module.'''
 +
 
 +
'''Author''' field shows author and '''License''' field shows the '''license''' of the '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''srcversion'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''srcversion field '''contains the source code version used to compile a''' module'''.
 +
 
 +
It is calculated automatically at build time.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''depends'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' depends''' field contains all '''modules''' on which this '''module '''depends.
 +
 
 +
It is shown empty here as this '''module''' does not depend on any other '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''retpoline'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| '''Retpoline''' field indicates that the '''module '''is '''compiled''' with '''retpoline '''method.
 +
 
 +
'''Modules''' must also be compiled with a '''retpoline-aware compiler.'''
 +
 
 +
Otherwise the '''kernel '''can be vulnerable.
 +
 
 +
'''Retpoline technique''' protects the kernel from the hacker’s attacks.
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''name'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''name''' field contains the '''name '''of a''' module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''vermagic'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This field shows the''' version magic''' number of a '''module.'''
 +
 
 +
This '''version magic''' number is used while loading the '''kernel module.'''
 +
 
 +
The '''version magic''' number of '''module''' and current '''kernel version '''should be the same.
 +
 
 +
Otherwise it will fail to load in the current '''kernel. '''
 +
|-
 +
| 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.'''
 +
 
 +
This '''command''' removes all '''object files''' that are created after the '''compilation.'''
 +
 
 +
'''Type ls.'''
 +
 
 +
Now there are no '''object files.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"|
 +
| style="border:0.5pt solid #000000;padding:0.176cm;"| With this, we come to the end of this tutorial. Let us summarize.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 6:
 +
 
 +
Summary:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| In this tutorial, we learned how to
 +
 
 +
* Implement a '''simple loadable module.'''
 +
* Create a '''Makefile'''.
 +
* Compile a '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 7:
 +
 
 +
Assignment:
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| As an assignment,
 +
 
 +
# Open the''' simple_module.c file'''
 +
# Change the module description''' '''using''' MODULE_DESCRIPTION macro '''
 +
# Run the '''modinfo command'''
 +
# See the output of description.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 8:
 +
 
 +
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 9:
 +
 
 +
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 10:
 +
 
 +
Forum questions:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * Do you have questions in THIS Spoken Tutorial?
 +
* Please visit this site
 +
* Choose the minute and second where you have the question.
 +
* Explain your question briefly.
 +
* The Spoken Tutorial project will ensure an answer
 +
* You will have to register to ask questions
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 11:
 +
 
 +
Forum for specific questions:
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * The Spoken Tutorial forum is for specific questions on this tutorial.
 +
* Please do not post unrelated and general questions on them.
 +
* This will help reduce the clutter.
 +
* With less clutter, we can use these discussions as instructional material.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 12:
 +
 
 +
Forum for specific questions:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * Do you have 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 13:
 +
 
 +
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 14:
 +
 
 +
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.
 +
 
 +
|}
 +
.
  
 
I have given the description as “'''First Linux kernel module”.'''
 
I have given the description as “'''First Linux kernel module”.'''
Line 164: Line 522:
 
If this '''function''' fails then the '''error '''will be returned.
 
If this '''function''' fails then the '''error '''will be returned.
  
−
It will return 0 to the '''kernel''' on successful execution.
+
It will '''return''' 0 to the '''kernel''' on successful execution.
 +
 
 +
Initialization function prints a simple message and return zero.
 +
 
 +
The '''module init''' '''macro''' is used to register the '''init function.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' void exit_func (void)'''
 +
 
 +
Highlight '''module_exit()'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' exit function '''will execute when the '''module '''is unloaded from the '''kernel'''.
 +
 
 +
It is mostly used to cleanup the '''resources''' acquired by the '''module'''
 +
 
 +
The''' exit function''' will undo whatever the''' init function '''did.
 +
 
 +
The '''module underscore exit macro is''' used to register the '''exit function. '''
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''printk'''
 +
 
 +
Highlight '''KERN_INFO'''
 +
 
 +
Press >> '''Ctrl + S'''
 +
 
 +
Press '''Enter'''
 +
 
 +
Click on '''close''' option.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| In '''kernel '''programming, '''printk '''is used as a printing''' function.'''
 +
 
 +
It is similar to '''printf function '''in '''C '''programming.
 +
 
 +
Using this '''function,''' string data will get loaded in the '''kernel''' log '''buffer'''.
 +
 
 +
'''printk''' has an optional prefix string, '''Loglevel '''such as''' KERN_INFO.'''
 +
 
 +
'''Loglevel '''specifies the type of message being sent to the kernel message log.
 +
 
 +
'''KERN underscore INFO''' is used for informational messages.
 +
 
 +
For more log levels, go through the '''Additional reading material''' link of this tutorial.
 +
 
 +
Press '''Ctrl + S''' keys to save the '''program '''.
 +
 
 +
Close the '''file.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"|
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Let us compile the code.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''gedit Makefile'''
 +
 
 +
Highlight the makefile
 +
 
 +
Press '''Enter'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| For that, we have to create a''' Makefile.'''
 +
 
 +
Type '''gedit Makefile '''
 +
 
 +
The '''Makefile''' is a special file containing '''shell '''commands.
 +
 
 +
Press '''Enter.'''
 +
 
 +
Create a '''Makefile '''where you have saved the '''simple_module dot c .'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Copy paste the makefile content
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type the '''code '''as shown.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''obj-m'''
 +
 
 +
Highlight '''simple_module.o'''
 +
 
 +
Highlight '''all:'''
 +
 
 +
Highlight '''clean:'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' obj hyphen m''' variable tells the '''kernel Makefile '''that this '''module '''needs to be compiled.
 +
 
 +
When you run the '''make''' '''all '''command''',''' then commands under '''all''' section will be executed.
 +
 
 +
If you run the '''make clean '''command, it executes commands under the '''clean '''section.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''-C'''
 +
 
 +
Highlight '''uname -r'''
 +
Highlight''' (PWD)'''
 +
Highlight '''M=$(PWD)'''
 +
Highlight''' modules'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Using '''hyphen C''', we are running '''make command '''inside the''' kernel source directory.'''
 +
 
 +
As you know,''' uname hyphen r''' finds the current '''Linux kernel''' version of a '''system.'''
 +
 
 +
'''PWD '''means the '''present working directory.'''
 +
 
 +
This option tells the '''kernel''' '''makefile''' that the '''source''' '''code '''for the driver is in '''PWD'''.
 +
 
 +
The word '''modules''' tell the '''kernel makefile''' to build the '''modules'''.
 +
 
 +
But it will not build the complete''' kernel source code.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''clean'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The word '''clean''' tells the '''kernel makefile '''to clean the generated '''object files.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Press >> '''Ctrl + S'''
 +
 
 +
Click on the '''close'''.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Save the '''file''' and close the '''editor'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Open the '''terminal'''
 +
 
 +
Type >> '''make all'''
 +
 
 +
Press '''Enter'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
 
 +
Let us compile the '''program''',
 +
 
 +
Type '''make space all.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type''' ls '''and''' '''Press''' Enter'''
 +
 
 +
Highlight''' ls '''
 +
 
 +
Show the output
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Now type''' ls.'''
 +
 
 +
This command lists the '''files''' in the current '''directory.'''
 +
 
 +
Here, you can see the number of '''files '''created in this '''directory'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' module.symvers'''
 +
 
 +
Highlight''' mod.c '''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' module.symvers''' file contains a list of all '''symbols'''
 +
 
 +
These '''symbols '''are exported from the '''kernel '''build.
 +
 
 +
The '''mod.c file '''contains information about the '''module'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' mod.o'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| '''Mod.o''' file is '''object file''' resulting from the compilation of the '''mod.c file.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' .o'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This''' object file''' is created from the compilation of the '''module source file'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' modules.order'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| It will list out the order in which the compilation and creation of the '''.ko file '''takes place.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' .ko'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This is the final '''kernel module''' binary that is loaded into the '''kernel.'''
 +
 
 +
|-
 +
| 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 '''>> modinfo simple_module.ko'''
 +
 
 +
Press '''Enter'''
 +
 
 +
Highlight '''modinfo'''
 +
 
 +
Highlight '''filename'''
 +
 
 +
Highlight '''description'''
 +
 
 +
Highlight '''author, license'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Let us see the details of a '''module'''.
 +
 
 +
Type''' modinfo space simple_module dot ko.'''
 +
 
 +
This command displays information about the '''Linux kernel module. '''
 +
 
 +
The '''filename''' field contains an absolute path to the .'''ko kernel''' '''object file.'''
 +
 
 +
This field displays a short description of a '''module.'''
 +
 
 +
Author field shows author and '''license '''field shows the '''license''' of the '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''srcversion'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''srcversion field '''contains the source code version used to compile a''' module'''.
 +
 
 +
It is calculated automatically at build time.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''depends'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' depends''' field contains all '''modules''' on which this '''module '''depends.
 +
 
 +
It is shown empty here as this '''module '''does not depend on any other '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''retpoline'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| '''Retpoline''' field indicates that the '''module '''is compiled with '''retpoline '''method.
 +
 
 +
'''Modules''' must also be compiled with a '''retpoline-aware compiler.'''
 +
 
 +
Otherwise the '''kernel '''can be vulnerable.
 +
 
 +
'''Retpoline technique''' protects the kernel from the hacker’s attacks.
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''name'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''name''' field contains the '''name '''of a''' module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''vermagic'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This field shows the''' version magic''' number of a '''module.'''
 +
 
 +
This '''version magic''' number is used while loading the '''kernel module.'''
 +
 
 +
The '''version magic''' number of '''module''' and current '''kernel version '''should be the same.
 +
 
 +
Otherwise it will fail to load in the current '''kernel. '''
 +
|-
 +
| 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.'''
 +
 
 +
This '''command''' removes all '''object files''' that are created after the '''compilation.'''
 +
 
 +
'''Type ls.'''
 +
 
 +
Now there are no '''object files.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"|
 +
| style="border:0.5pt solid #000000;padding:0.176cm;"| With this, we come to the end of this tutorial. Let us summarize.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 6:
 +
 
 +
Summary:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| In this tutorial, we learned how to
 +
 
 +
* Implement a '''simple loadable module.'''
 +
* Create a '''Makefile'''.
 +
* Compile a '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 7:
 +
 
 +
Assignment:
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| As an assignment,
 +
 
 +
# Open the''' simple_module.c file'''
 +
# Change the module description''' '''using''' MODULE_DESCRIPTION macro '''
 +
# Run the '''modinfo''' command
 +
# See the output of description.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 8:
 +
 
 +
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 9:
 +
 
 +
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 10:
 +
 
 +
Forum questions:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * Do you have questions in THIS Spoken Tutorial?
 +
* Please visit this site
 +
* Choose the minute and second where you have the question.
 +
* Explain your question briefly.
 +
* The Spoken Tutorial project will ensure an answer
 +
* You will have to register to ask questions
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 11:
 +
 
 +
Forum for specific questions:
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * The Spoken Tutorial forum is for specific questions on this tutorial.
 +
* Please do not post unrelated and general questions on them.
 +
* This will help reduce the clutter.
 +
* With less clutter, we can use these discussions as instructional material.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 12:
 +
 
 +
Forum for specific questions:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * Do you have 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 13:
 +
 
 +
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 14:
 +
 
 +
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.
 +
 
 +
|}
 +
.
 +
 
 +
I have given the description as “'''First Linux kernel module”.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''static int init_func(void)'''
 +
 
 +
Highlight '''return(0)'''
 +
 
 +
Highlight '''module_init()'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''init function '''will execute when a '''module '''is loaded into the '''kernel'''.
 +
 
 +
So it is called as an '''initialization''' '''function''' of a '''module'''.
 +
 
 +
If this '''function''' fails then the '''error '''will be returned.
 +
 
 +
It will '''return''' 0 to the '''kernel''' on successful '''execution'''.
 +
 
 +
'''Initialization function''' prints a simple message and return zero.
 +
 
 +
The '''module init''' '''macro''' is used to register the '''init function.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' void exit_func (void)'''
 +
 
 +
Highlight '''module_exit()'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' exit function '''will execute when the '''module '''is unloaded from the '''kernel'''.
 +
 
 +
It is mostly used to cleanup the '''resources''' acquired by the '''module'''
 +
 
 +
The''' exit function''' will undo whatever the''' init function '''did.
 +
 
 +
The '''module underscore exit macro is''' used to register the '''exit function. '''
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''printk'''
 +
 
 +
Highlight '''KERN_INFO'''
 +
 
 +
Press >> '''Ctrl + S'''
 +
 
 +
Press '''Enter'''
 +
 
 +
Click on '''close''' option.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| In '''kernel '''programming, '''printk '''is used as a printing''' function.'''
 +
 
 +
It is similar to '''printf function '''in '''C '''programming.
 +
 
 +
Using this '''function,''' string data will get loaded in the '''kernel''' log '''buffer'''.
 +
 
 +
'''printk''' has an optional prefix string, '''Loglevel '''such as''' KERN_INFO.'''
 +
 
 +
'''Loglevel '''specifies the type of message being sent to the kernel message log.
 +
 
 +
'''KERN underscore INFO''' is used for informational messages.
 +
 
 +
For more log levels, go through the '''Additional reading material''' link of this tutorial.
 +
 
 +
Press '''Ctrl + S''' keys to save the '''program '''.
 +
 
 +
Close the '''file.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"|
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Let us compile the code.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''gedit Makefile'''
 +
 
 +
Highlight the makefile
 +
 
 +
Press '''Enter'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| For that, we have to create a''' Makefile.'''
 +
 
 +
Type '''gedit Makefile '''
 +
 
 +
The '''Makefile''' is a special file containing '''shell '''commands.
 +
 
 +
Press '''Enter.'''
 +
 
 +
Create a '''Makefile '''where you have saved the '''simple_module dot c .'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Copy paste the makefile content
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type the '''code '''as shown.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''obj-m'''
 +
 
 +
Highlight '''simple_module.o'''
 +
 
 +
Highlight '''all:'''
 +
 
 +
Highlight '''clean:'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' obj hyphen m''' variable tells the '''kernel Makefile '''that this '''module '''needs to be compiled.
 +
 
 +
When you run the '''make''' '''all '''command''',''' then commands under '''all''' section will be executed.
 +
 
 +
If you run the '''make clean '''command, it executes commands under the '''clean '''section.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''-C'''
 +
 
 +
Highlight '''uname -r'''
 +
Highlight''' (PWD)'''
 +
Highlight '''M=$(PWD)'''
 +
Highlight''' modules'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Using '''hyphen C''', we are running '''make command '''inside the''' kernel source directory.'''
 +
 
 +
As you know,''' uname hyphen r''' finds the current '''Linux kernel''' version of a '''system.'''
 +
 
 +
'''PWD '''means the '''present working directory.'''
 +
 
 +
This option tells the '''kernel''' '''makefile''' that the '''source''' '''code '''for the driver is in '''PWD'''.
 +
 
 +
The word '''modules''' tell the '''kernel makefile''' to build the '''modules'''.
 +
 
 +
But it will not build the complete''' kernel source code.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''clean'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The word '''clean''' tells the '''kernel makefile '''to clean the generated '''object files.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Press >> '''Ctrl + S'''
 +
 
 +
Click on the '''close'''.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Save the '''file''' and close the '''editor'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Open the '''terminal'''
 +
 
 +
Type >> '''make all'''
 +
 
 +
Press '''Enter'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
 
 +
Let us compile the '''program''',
 +
 
 +
Type '''make space all.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type''' ls '''and''' '''Press''' Enter'''
 +
 
 +
Highlight''' ls '''
 +
 
 +
Show the output
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Now type''' ls.'''
 +
 
 +
This command lists the '''files''' in the current '''directory.'''
 +
 
 +
Here, you can see the number of '''files '''created in this '''directory'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' module.symvers'''
 +
 
 +
Highlight''' mod.c '''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' module.symvers''' file contains a list of all '''symbols'''
 +
 
 +
These '''symbols '''are exported from the '''kernel '''build.
 +
 
 +
The '''mod.c file '''contains information about the '''module'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' mod.o'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| '''Mod.o''' file is '''object file''' resulting from the compilation of the '''mod.c file.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' .o'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This''' object file''' is created from the compilation of the '''module source file'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' modules.order'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| It will list out the order in which the compilation and creation of the '''.ko file '''takes place.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' .ko'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This is the final '''kernel module''' binary that is loaded into the '''kernel.'''
 +
 
 +
|-
 +
| 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 '''>> modinfo simple_module.ko'''
 +
 
 +
Press '''Enter'''
 +
 
 +
Highlight '''modinfo'''
 +
 
 +
Highlight '''filename'''
 +
 
 +
Highlight '''description'''
 +
 
 +
Highlight '''author, license'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Let us see the details of a '''module'''.
 +
 
 +
Type''' modinfo space simple_module dot ko.'''
 +
 
 +
This command displays information about the '''Linux kernel module. '''
 +
 
 +
The '''filename''' field contains an absolute path to the .'''ko kernel''' '''object file.'''
 +
 
 +
This field displays a short description of a '''module.'''
 +
 
 +
Author field shows author and '''license '''field shows the '''license''' of the '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''srcversion'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''srcversion field '''contains the source code version used to compile a''' module'''.
 +
 
 +
It is calculated automatically at build time.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''depends'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' depends''' field contains all '''modules''' on which this '''module '''depends.
 +
 
 +
It is shown empty here as this '''module '''does not depend on any other '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''retpoline'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| '''Retpoline''' field indicates that the '''module '''is compiled with '''retpoline '''method.
 +
 
 +
'''Modules''' must also be compiled with a '''retpoline-aware compiler.'''
 +
 
 +
Otherwise the '''kernel '''can be vulnerable.
 +
 
 +
'''Retpoline technique''' protects the kernel from the hacker’s attacks.
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''name'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''name''' field contains the '''name '''of a''' module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''vermagic'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This field shows the''' version magic''' number of a '''module.'''
 +
 
 +
This '''version magic''' number is used while loading the '''kernel module.'''
 +
 
 +
The '''version magic''' number of '''module''' and current '''kernel version '''should be the same.
 +
 
 +
Otherwise it will fail to load in the current '''kernel. '''
 +
|-
 +
| 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.'''
 +
 
 +
This '''command''' removes all '''object files''' that are created after the '''compilation.'''
 +
 
 +
'''Type ls.'''
 +
 
 +
Now there are no '''object files.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"|
 +
| style="border:0.5pt solid #000000;padding:0.176cm;"| With this, we come to the end of this tutorial. Let us summarize.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 6:
 +
 
 +
Summary:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| In this tutorial, we learned how to
 +
 
 +
* Implement a '''simple loadable module.'''
 +
* Create a '''Makefile'''.
 +
* Compile a '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 7:
 +
 
 +
Assignment:
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| As an assignment,
 +
 
 +
# Open the''' simple_module.c file'''
 +
# Change the module description''' '''using''' MODULE_DESCRIPTION macro '''
 +
# Run the '''modinfo''' command
 +
# See the output of description.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 8:
 +
 
 +
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 9:
 +
 
 +
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 10:
 +
 
 +
Forum questions:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * Do you have questions in THIS Spoken Tutorial?
 +
* Please visit this site
 +
* Choose the minute and second where you have the question.
 +
* Explain your question briefly.
 +
* The Spoken Tutorial project will ensure an answer
 +
* You will have to register to ask questions
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 11:
 +
 
 +
Forum for specific questions:
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * The Spoken Tutorial forum is for specific questions on this tutorial.
 +
* Please do not post unrelated and general questions on them.
 +
* This will help reduce the clutter.
 +
* With less clutter, we can use these discussions as instructional material.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 12:
 +
 
 +
Forum for specific questions:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * Do you have 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 13:
 +
 
 +
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 14:
 +
 
 +
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. .
 +
 
 +
I have given the description as “'''First Linux kernel module”.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''static int init_func(void)'''
 +
 
 +
Highlight '''return(0)'''
 +
 
 +
Highlight '''module_init()'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''init function '''will execute when a '''module '''is loaded into the '''kernel'''.
 +
 
 +
So it is called as an '''initialization''' '''function''' of a '''module'''.
 +
 
 +
If this '''function''' fails then the '''error '''will be '''returned'''.
 +
 
 +
It will '''return''' 0 to the '''kernel''' on successful '''execution'''.
 +
 
 +
'''Initialization function''' prints a simple message and '''return''' zero.
 +
 
 +
The '''module init''' '''macro''' is used to register the '''init function.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' void exit_func (void)'''
 +
 
 +
Highlight '''module_exit()'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' exit function '''will execute when the '''module '''is unloaded from the '''kernel'''.
 +
 
 +
It is mostly used to cleanup the '''resources''' acquired by the '''module'''
 +
 
 +
The''' exit function''' will undo whatever the''' init function '''did.
 +
 
 +
The '''module underscore exit macro is''' used to register the '''exit function. '''
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''printk'''
 +
 
 +
Highlight '''KERN_INFO'''
 +
 
 +
Press >> '''Ctrl + S'''
 +
 
 +
Press '''Enter'''
 +
 
 +
Click on '''close''' option.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| In '''kernel '''programming, '''printk '''is used as a printing''' function.'''
 +
 
 +
It is similar to '''printf function '''in '''C '''programming.
 +
 
 +
Using this '''function,''' string data will get loaded in the '''kernel''' log '''buffer'''.
 +
 
 +
'''printk''' has an optional prefix string, '''Loglevel '''such as''' KERN_INFO.'''
 +
 
 +
'''Loglevel '''specifies the type of message being sent to the kernel message log.
 +
 
 +
'''KERN underscore INFO''' is used for informational messages.
 +
 
 +
For more log levels, go through the '''Additional reading material''' link of this tutorial.
 +
 
 +
Press '''Ctrl + S''' keys to save the '''program '''.
 +
 
 +
Close the '''file.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"|
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Let us compile the code.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''gedit Makefile'''
 +
 
 +
Highlight the makefile
 +
 
 +
Press '''Enter'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| For that, we have to create a''' Makefile.'''
 +
 
 +
Type '''gedit Makefile '''
 +
 
 +
The '''Makefile''' is a special file containing '''shell '''commands.
 +
 
 +
Press '''Enter.'''
 +
 
 +
Create a '''Makefile '''where you have saved the '''simple_module dot c .'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Copy paste the makefile content
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type the '''code '''as shown.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''obj-m'''
 +
 
 +
Highlight '''simple_module.o'''
 +
 
 +
Highlight '''all:'''
 +
 
 +
Highlight '''clean:'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' obj hyphen m''' variable tells the '''kernel Makefile '''that this '''module '''needs to be compiled.
 +
 
 +
When you run the '''make''' '''all '''command''',''' then commands under '''all''' section will be executed.
 +
 
 +
If you run the '''make clean '''command, it executes commands under the '''clean '''section.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''-C'''
 +
 
 +
Highlight '''uname -r'''
 +
Highlight''' (PWD)'''
 +
Highlight '''M=$(PWD)'''
 +
Highlight''' modules'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Using '''hyphen C''', we are running '''make command '''inside the''' kernel source directory.'''
 +
 
 +
As you know,''' uname hyphen r''' finds the current '''Linux kernel''' version of a '''system.'''
 +
 
 +
'''PWD '''means the '''present working directory.'''
 +
 
 +
This option tells the '''kernel''' '''makefile''' that the '''source''' '''code '''for the driver is in '''PWD'''.
 +
 
 +
The word '''modules''' tell the '''kernel makefile''' to build the '''modules'''.
 +
 
 +
But it will not build the complete''' kernel source code.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''clean'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The word '''clean''' tells the '''kernel makefile '''to clean the generated '''object files.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Press >> '''Ctrl + S'''
 +
 
 +
Click on the '''close'''.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Save the '''file''' and close the '''editor'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Open the '''terminal'''
 +
 
 +
Type >> '''make all'''
 +
 
 +
Press '''Enter'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
 
 +
Let us compile the '''program''',
 +
 
 +
Type '''make space all.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type''' ls '''and''' '''Press''' Enter'''
 +
 
 +
Highlight''' ls '''
 +
 
 +
Show the output
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Now type''' ls.'''
 +
 
 +
This command lists the '''files''' in the current '''directory.'''
 +
 
 +
Here, you can see the number of '''files '''created in this '''directory'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' module.symvers'''
 +
 
 +
Highlight''' mod.c '''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' module.symvers''' file contains a list of all '''symbols'''
 +
 
 +
These '''symbols '''are exported from the '''kernel '''build.
 +
 
 +
The '''mod.c file '''contains information about the '''module'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' mod.o'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| '''Mod.o''' file is '''object file''' resulting from the compilation of the '''mod.c file.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' .o'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This''' object file''' is created from the compilation of the '''module source file'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' modules.order'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| It will list out the order in which the compilation and creation of the '''.ko file '''takes place.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' .ko'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This is the final '''kernel module''' binary that is loaded into the '''kernel.'''
 +
 
 +
|-
 +
| 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 '''>> modinfo simple_module.ko'''
 +
 
 +
Press '''Enter'''
 +
 
 +
Highlight '''modinfo'''
 +
 
 +
Highlight '''filename'''
 +
 
 +
Highlight '''description'''
 +
 
 +
Highlight '''author, license'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Let us see the details of a '''module'''.
 +
 
 +
Type''' modinfo space simple_module dot ko.'''
 +
 
 +
This command displays information about the '''Linux kernel module. '''
 +
 
 +
The '''filename''' field contains an absolute path to the .'''ko kernel''' '''object file.'''
 +
 
 +
This field displays a short description of a '''module.'''
 +
 
 +
Author field shows author and '''license '''field shows the '''license''' of the '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''srcversion'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''srcversion field '''contains the source code version used to compile a''' module'''.
 +
 
 +
It is calculated automatically at build time.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''depends'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' depends''' field contains all '''modules''' on which this '''module '''depends.
 +
 
 +
It is shown empty here as this '''module '''does not depend on any other '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''retpoline'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| '''Retpoline''' field indicates that the '''module '''is compiled with '''retpoline '''method.
 +
 
 +
'''Modules''' must also be compiled with a '''retpoline-aware compiler.'''
 +
 
 +
Otherwise the '''kernel '''can be vulnerable.
 +
 
 +
'''Retpoline technique''' protects the kernel from the hacker’s attacks.
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''name'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''name''' field contains the '''name '''of a''' module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''vermagic'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This field shows the''' version magic''' number of a '''module.'''
 +
 
 +
This '''version magic''' number is used while loading the '''kernel module.'''
 +
 
 +
The '''version magic''' number of '''module''' and current '''kernel version '''should be the same.
 +
 
 +
Otherwise it will fail to load in the current '''kernel. '''
 +
|-
 +
| 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.'''
 +
 
 +
This '''command''' removes all '''object files''' that are created after the '''compilation.'''
 +
 
 +
'''Type ls.'''
 +
 
 +
Now there are no '''object files.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"|
 +
| style="border:0.5pt solid #000000;padding:0.176cm;"| With this, we come to the end of this tutorial. Let us summarize.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 6:
 +
 
 +
Summary:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| In this tutorial, we learned how to
 +
 
 +
* Implement a '''simple loadable module.'''
 +
* Create a '''Makefile'''.
 +
* Compile a '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 7:
 +
 
 +
Assignment:
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| As an assignment,
 +
 
 +
# Open the''' simple_module.c file'''
 +
# Change the module description''' '''using''' MODULE_DESCRIPTION macro '''
 +
# Run the '''modinfo''' command
 +
# See the output of description.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 8:
 +
 
 +
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 9:
 +
 
 +
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 10:
 +
 
 +
Forum questions:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * Do you have questions in THIS Spoken Tutorial?
 +
* Please visit this site
 +
* Choose the minute and second where you have the question.
 +
* Explain your question briefly.
 +
* The Spoken Tutorial project will ensure an answer
 +
* You will have to register to ask questions
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 11:
 +
 
 +
Forum for specific questions:
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * The Spoken Tutorial forum is for specific questions on this tutorial.
 +
* Please do not post unrelated and general questions on them.
 +
* This will help reduce the clutter.
 +
* With less clutter, we can use these discussions as instructional material.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 12:
 +
 
 +
Forum for specific questions:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * Do you have 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 13:
 +
 
 +
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 14:
 +
 
 +
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.
 +
 
 +
|}
 +
 
 +
 
 +
|}
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''static int init_func(void)'''
 +
 
 +
Highlight '''return(0)'''
 +
 
 +
Highlight '''module_init()'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''init function '''will execute when a '''module '''is loaded into the '''kernel'''.
 +
 
 +
So it is called as an '''initialization''' '''function''' of a '''module'''.
 +
 
 +
If this '''function''' fails then the '''error '''will be returned. .
 +
 
 +
I have given the description as “'''First Linux kernel module”.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''static int init_func(void)'''
 +
 
 +
Highlight '''return(0)'''
 +
 
 +
Highlight '''module_init()'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''init function '''will execute when a '''module '''is loaded into the '''kernel'''.
 +
 
 +
So it is called as an '''initialization''' '''function''' of a '''module'''.
 +
 
 +
If this '''function''' fails then the '''error '''will be '''returned'''.
 +
 
 +
It will '''return''' 0 to the '''kernel''' on successful '''execution'''.
 +
 
 +
Initialization function prints a simple message and return zero.
 +
 
 +
The '''module init''' '''macro''' is used to register the '''init function.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' void exit_func (void)'''
 +
 
 +
Highlight '''module_exit()'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' exit function '''will execute when the '''module '''is unloaded from the '''kernel'''.
 +
 
 +
It is mostly used to cleanup the '''resources''' acquired by the '''module'''
 +
 
 +
The''' exit function''' will undo whatever the''' init function '''did.
 +
 
 +
The '''module underscore exit macro is''' used to register the '''exit function. '''
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''printk'''
 +
 
 +
Highlight '''KERN_INFO'''
 +
 
 +
Press >> '''Ctrl + S'''
 +
 
 +
Press '''Enter'''
 +
 
 +
Click on '''close''' option.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| In '''kernel '''programming, '''printk '''is used as a printing''' function.'''
 +
 
 +
It is similar to '''printf function '''in '''C '''programming.
 +
 
 +
Using this '''function,''' string data will get loaded in the '''kernel''' log '''buffer'''.
 +
 
 +
'''printk''' has an optional prefix string, '''Loglevel '''such as''' KERN_INFO.'''
 +
 
 +
'''Loglevel '''specifies the type of message being sent to the kernel message log.
 +
 
 +
'''KERN underscore INFO''' is used for informational messages.
 +
 
 +
For more log levels, go through the '''Additional reading material''' link of this tutorial.
 +
 
 +
Press '''Ctrl + S''' keys to save the '''program '''.
 +
 
 +
Close the '''file.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"|
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Let us compile the code.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''gedit Makefile'''
 +
 
 +
Highlight the makefile
 +
 
 +
Press '''Enter'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| For that, we have to create a''' Makefile.'''
 +
 
 +
Type '''gedit Makefile '''
 +
 
 +
The '''Makefile''' is a special file containing '''shell '''commands.
 +
 
 +
Press '''Enter.'''
 +
 
 +
Create a '''Makefile '''where you have saved the '''simple_module dot c .'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Copy paste the makefile content
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type the '''code '''as shown.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''obj-m'''
 +
 
 +
Highlight '''simple_module.o'''
 +
 
 +
Highlight '''all:'''
 +
 
 +
Highlight '''clean:'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' obj hyphen m''' variable tells the '''kernel Makefile '''that this '''module '''needs to be compiled.
 +
 
 +
When you run the '''make''' '''all '''command''',''' then commands under '''all''' section will be executed.
 +
 
 +
If you run the '''make clean '''command, it executes commands under the '''clean '''section.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''-C'''
 +
 
 +
Highlight '''uname -r'''
 +
Highlight''' (PWD)'''
 +
Highlight '''M=$(PWD)'''
 +
Highlight''' modules'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Using '''hyphen C''', we are running '''make command '''inside the''' kernel source directory.'''
 +
 
 +
As you know,''' uname hyphen r''' finds the current '''Linux kernel''' version of a '''system.'''
 +
 
 +
'''PWD '''means the '''present working directory.'''
 +
 
 +
This option tells the '''kernel''' '''makefile''' that the '''source''' '''code '''for the driver is in '''PWD'''.
 +
 
 +
The word '''modules''' tell the '''kernel makefile''' to build the '''modules'''.
 +
 
 +
But it will not build the complete''' kernel source code.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''clean'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The word '''clean''' tells the '''kernel makefile '''to clean the generated '''object files.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Press >> '''Ctrl + S'''
 +
 
 +
Click on the '''close'''.
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Save the '''file''' and close the '''editor'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Open the '''terminal'''
 +
 
 +
Type >> '''make all'''
 +
 
 +
Press '''Enter'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the '''terminal'''.
 +
 
 +
Let us compile the '''program''',
 +
 
 +
Type '''make space all.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Type''' ls '''and''' '''Press''' Enter'''
 +
 
 +
Highlight''' ls '''
 +
 
 +
Show the output
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Now type''' ls.'''
 +
 
 +
This command lists the '''files''' in the current '''directory.'''
 +
 
 +
Here, you can see the number of '''files '''created in this '''directory'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' module.symvers'''
 +
 
 +
Highlight''' mod.c '''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' module.symvers''' file contains a list of all '''symbols'''
 +
 
 +
These '''symbols '''are exported from the '''kernel '''build.
 +
 
 +
The '''mod.c file '''contains information about the '''module'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' mod.o'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| '''Mod.o''' file is '''object file''' resulting from the compilation of the '''mod.c file.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' .o'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This''' object file''' is created from the compilation of the '''module source file'''.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' modules.order'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| It will list out the order in which the compilation and creation of the '''.ko file '''takes place.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' .ko'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This is the final '''kernel module''' binary that is loaded into the '''kernel.'''
 +
 
 +
|-
 +
| 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 '''>> modinfo simple_module.ko'''
 +
 
 +
Press '''Enter'''
 +
 
 +
Highlight '''modinfo'''
 +
 
 +
Highlight '''filename'''
 +
 
 +
Highlight '''description'''
 +
 
 +
Highlight '''author, license'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Let us see the details of a '''module'''.
 +
 
 +
Type''' modinfo space simple_module dot ko.'''
 +
 
 +
This command displays information about the '''Linux kernel module. '''
 +
 
 +
The '''filename''' field contains an absolute path to the .'''ko kernel''' '''object file.'''
 +
 
 +
This field displays a short description of a '''module.'''
 +
 
 +
Author field shows author and '''license '''field shows the '''license''' of the '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''srcversion'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''srcversion field '''contains the source code version used to compile a''' module'''.
 +
 
 +
It is calculated automatically at build time.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''depends'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The''' depends''' field contains all '''modules''' on which this '''module '''depends.
 +
 
 +
It is shown empty here as this '''module '''does not depend on any other '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''retpoline'''
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| '''Retpoline''' field indicates that the '''module '''is compiled with '''retpoline '''method.
 +
 
 +
'''Modules''' must also be compiled with a '''retpoline-aware compiler.'''
 +
 
 +
Otherwise the '''kernel '''can be vulnerable.
 +
 
 +
'''Retpoline technique''' protects the kernel from the hacker’s attacks.
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''name'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| The '''name''' field contains the '''name '''of a''' module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''vermagic'''
 +
| style="border:1pt solid #000000;padding:0.176cm;"| This field shows the''' version magic''' number of a '''module.'''
 +
 
 +
This '''version magic''' number is used while loading the '''kernel module.'''
 +
 
 +
The '''version magic''' number of '''module''' and current '''kernel version '''should be the same.
 +
 
 +
Otherwise it will fail to load in the current '''kernel. '''
 +
|-
 +
| 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.'''
 +
 
 +
This '''command''' removes all '''object files''' that are created after the '''compilation.'''
 +
 
 +
'''Type ls.'''
 +
 
 +
Now there are no '''object files.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"|
 +
| style="border:0.5pt solid #000000;padding:0.176cm;"| With this, we come to the end of this tutorial. Let us summarize.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 6:
 +
 
 +
Summary:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| In this tutorial, we learned how to
 +
 
 +
* Implement a '''simple loadable module.'''
 +
* Create a '''Makefile'''.
 +
* Compile a '''module.'''
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 7:
 +
 
 +
Assignment:
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| As an assignment,
 +
 
 +
# Open the''' simple_module.c file'''
 +
# Change the module description''' '''using''' MODULE_DESCRIPTION macro '''
 +
# Run the '''modinfo''' command
 +
# See the output of description.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 8:
 +
 
 +
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 9:
 +
 
 +
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 10:
 +
 
 +
Forum questions:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * Do you have questions in THIS Spoken Tutorial?
 +
* Please visit this site
 +
* Choose the minute and second where you have the question.
 +
* Explain your question briefly.
 +
* The Spoken Tutorial project will ensure an answer
 +
* You will have to register to ask questions
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 11:
 +
 
 +
Forum for specific questions:
 +
 
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * The Spoken Tutorial forum is for specific questions on this tutorial.
 +
* Please do not post unrelated and general questions on them.
 +
* This will help reduce the clutter.
 +
* With less clutter, we can use these discussions as instructional material.
 +
 
 +
|-
 +
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 12:
 +
 
 +
Forum for specific questions:
 +
| style="border:1pt solid #000000;padding:0.176cm;"| * Do you have 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 13:
 +
 
 +
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 14:
 +
 
 +
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.
 +
 
 +
|}
 +
 
 +
 
 +
It will '''return''' 0 to the '''kernel''' on successful execution.
  
 
Initialization function prints a simple message and return zero.  
 
Initialization function prints a simple message and return zero.  

Revision as of 13:12, 10 July 2020

I have given the description as “First Linux kernel module”.
Visual cue Narration
Slide 1:

Welcome slide:

Welcome to the spoken tutorial on Simple Loadable Module.
Slide 2:

Learning objectives:

  • Implement a simple loadable module.
  • Create the Makefile.
  • Compile the module.
In this tutorial, we will learn how to,
  • Implement a simple loadable module.
  • Create a Makefile.
  • Compile a module.
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.
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.
Slide 4:

Prerequisites:

To follow this tutorial, you should be familiar with:

  • C programming language and
  • basics of Linux kernel
To follow this tutorial, you should be familiar with:
  • C programming language and
  • basics of Linux kernel

If not, then go through the C/C++ and Linux spoken tutorials on this website

Slide 5:

Gedit Installation:

  • To proceed further, make sure that gedit is installed on your system.
  • If not, to do the installation, follow the instructions in gedit series on this https://spoken-tutorial.org
  • To proceed further, make sure that Gedit is installed on your system.
  • If not, to do the installation, follow the instructions in Gedit series on this website.
Slide 6:

What is a kernel module?

  • Code that is added to the kernel at runtime is called a module.
  • It extends the functionality of the kernel without the need to reboot the system.
  • It communicates with the base kernel to complete their functions.
Narration only I’ll start with a simple example to explain how to create a module.
Point to the folder and file in desktop I have saved a file simple_module dot c in a folder DeviceDriver in Desktop.
Slide:

Code file - sample_module.c

Please download simple_module dot c from the Code files link of this tutorial.

Make use of this file while practising.

Remember the file path.

Type gedit simple_module dot c and press Enter.

Text box

Let us open this file.

Open the terminal by pressing Ctrl+Alt+T keys simultaneously.

Press the Enter key after every command.

Go to the folder where simple_module dot c is saved.

Type gedit simple_module dot c

Let us understand the code now.
Show the program


Highlight <linux/init.h>


Highlight <linux/module.h>


Highlight <linux/kernel.h>

At the start of the program, there are some header files.

Init dot h file is used to start the init process.

The module dot h file contains functions related to the modules.

The kernel dot h file contains functions such as printk.

Highlight MODULE_LICENSE(“GPL”)

Highlight GPL

Next line of code is about GPL.

GPL means GNU Public License.

It is otherwise called as GNU, which is a free and open-source license.

Highlight MODULE_AUTHOR You can give the author name for your module using this macro as shown here.
Highlight MODULE_DESCRIPTION You can simply describe your module using this macro.

I have given the description as “First Linux kernel module”.

Highlight static int init_func(void)

Highlight return(0)

Highlight module_init()

The init function will execute when a module is loaded into the kernel.

So it is called as an initialization function of a module.

If this function fails then the error will be returned.

It will return 0 to the kernel on successful execution.

Initialization function prints a simple message and returns zero.

The module init macro is used to register the init function.

Highlight void exit_func (void)

Highlight module_exit()

The exit function will execute when the module is unloaded from the kernel.

It is mostly used to cleanup the resources acquired by the module

The exit function will undo whatever the init function did.

The module underscore exit macro is used to register the exit function.

Highlight printk

Highlight KERN_INFO

Press >> Ctrl + S

Press Enter

Click on close option.

In kernel programming, printk is used as a printing function.

It is similar to printf function in C programming.

Using this function, string data will get loaded in the kernel log buffer.

printk has an optional prefix string, Loglevel such as KERN_INFO.

Loglevel specifies the type of message being sent to the kernel message log.

KERN underscore INFO is used for informational messages.

For more log levels, go through the Additional reading material link of this tutorial.

Press Ctrl + S keys to save the program .

Close the file.

Switch back to the terminal. Switch back to the terminal.
Let us compile the code.
Type >> gedit Makefile

Highlight the makefile

Press Enter

For that, we have to create a Makefile.

Type gedit Makefile

The Makefile is a special file containing shell commands.

Press Enter.

Create a Makefile where you have saved the simple_module dot c .

Copy paste the makefile content Type the code as shown.
Highlight obj-m

Highlight simple_module.o

Highlight all:

Highlight clean:

The obj hyphen m variable tells the kernel Makefile that this module needs to be compiled.

When you run the make all command, then commands under all section will be executed.

If you run the make clean command, it executes commands under the clean section.

Highlight -C

Highlight uname -r Highlight (PWD) Highlight M=$(PWD) Highlight modules

Using hyphen C, we are running make command inside the kernel source directory.

As you know, uname hyphen r finds the current Linux kernel version of a system.

PWD means the present working directory.

This option tells the kernel makefile that the source code for the driver is in PWD.

The word modules tell the kernel makefile to build the modules.

But it will not build the complete kernel source code.

Highlight clean The word clean tells the kernel makefile to clean the generated object files.
Press >> Ctrl + S

Click on the close.

Save the file and close the editor.
Open the terminal

Type >> make all

Press Enter

Switch back to the terminal.

Let us compile the program.

Type make space all.

Type ls and press Enter

Highlight ls

Show the output

Now type ls.

This command lists the files in the current directory.

Here, you can see the number of files created in this directory.

Highlight module.symvers

Highlight mod.c

The module.symvers file contains a list of all symbols

These symbols are exported from the kernel build.

The mod.c file contains information about the module.

Highlight mod.o Mod.o file is object file resulting from the compilation of the mod.c file.
Highlight .o This object file is created from the compilation of the module source file.
Highlight modules.order It will list out the order in which the compilation and creation of the .ko file takes place.
Highlight .ko This is the final kernel module binary that is loaded into the kernel.
Type >> clear

Press Enter

Clear the screen.
Type >> modinfo simple_module.ko

Press Enter

Highlight modinfo

Highlight filename

Highlight description

Highlight author, license

Let us see the details of a module.

Type modinfo space simple_module dot ko.

This command displays information about the Linux kernel module.

The filename field contains an absolute path to the .ko kernel object file.

This field displays a short description of a module.

Author field shows author and License field shows the license of the module.

Highlight srcversion The srcversion field contains the source code version used to compile a module.

It is calculated automatically at build time.

Highlight depends The depends field contains all modules on which this module depends.

It is shown empty here as this module does not depend on any other module.

Highlight retpoline Retpoline field indicates that the module is compiled with retpoline method.

Modules must also be compiled with a retpoline-aware compiler.

Otherwise the kernel can be vulnerable.

Retpoline technique protects the kernel from the hacker’s attacks.

Highlight name The name field contains the name of a module.
Highlight vermagic This field shows the version magic number of a module.

This version magic number is used while loading the kernel module.

The version magic number of module and current kernel version should be the same.

Otherwise it will fail to load in the current kernel.

Type >> make clean

Press Enter

Type make space clean.

This command removes all object files that are created after the compilation.

Type ls.

Now there are no object files.

With this, we come to the end of this tutorial. Let us summarize.
Slide 6:

Summary:

In this tutorial, we learned how to
  • Implement a simple loadable module.
  • Create a Makefile.
  • Compile a module.
Slide 7:

Assignment:

As an assignment,
  1. Open the simple_module.c file
  2. Change the module description using MODULE_DESCRIPTION macro
  3. Run the modinfo command
  4. See the output of description.
Slide 8:

About Spoken Tutorial Project:

The video at the following link summarizes the Spoken Tutorial project.

Please download and watch it.

Slide 9:

Spoken Tutorial workshops:

The Spoken Tutorial Project Team:
  • conducts workshops and
  • gives certificates.

For more details, please write to us.

Slide 10:

Forum questions:

* Do you have questions in THIS Spoken Tutorial?
  • Please visit this site
  • Choose the minute and second where you have the question.
  • Explain your question briefly.
  • The Spoken Tutorial project will ensure an answer
  • You will have to register to ask questions
Slide 11:

Forum for specific questions:

* The Spoken Tutorial forum is for specific questions on this tutorial.
  • Please do not post unrelated and general questions on them.
  • This will help reduce the clutter.
  • With less clutter, we can use these discussions as instructional material.
Slide 12:

Forum for specific questions:

* Do you have general or technical questions on Embedded Linux Device Driver?
  • Please visit the FOSSEE forum and post your question.
Slide 13:

Acknowledgment:

Spoken Tutorial project is funded by MHRD, Government of India.
Slide 14:

Thank you slide:

This tutorial has been contributed by FOSSEE and Spoken Tutorial Project, IIT Bombay.

This is Mayuri Panchakshari signing off.

Thanks for watching. 

.

I have given the description as “First Linux kernel module”.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight static int init_func(void)

Highlight return(0)

Highlight module_init() | style="border:1pt solid #000000;padding:0.176cm;"| The init function will execute when a module is loaded into the kernel.

So it is called as an initialization function of a module.

If this function fails then the error will be returned.

It will return 0 to the kernel on successful execution.

Initialization function prints a simple message and return zero.

The module init macro is used to register the init function.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight void exit_func (void)

Highlight module_exit() | style="border:1pt solid #000000;padding:0.176cm;"| The exit function will execute when the module is unloaded from the kernel.

It is mostly used to cleanup the resources acquired by the module

The exit function will undo whatever the init function did.

The module underscore exit macro is used to register the exit function. |- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight printk

Highlight KERN_INFO

Press >> Ctrl + S

Press Enter

Click on close option. | style="border:1pt solid #000000;padding:0.176cm;"| In kernel programming, printk is used as a printing function.

It is similar to printf function in C programming.

Using this function, string data will get loaded in the kernel log buffer.

printk has an optional prefix string, Loglevel such as KERN_INFO.

Loglevel specifies the type of message being sent to the kernel message log.

KERN underscore INFO is used for informational messages.

For more log levels, go through the Additional reading material link of this tutorial.

Press Ctrl + S keys to save the program .

Close the file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal. | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal. |- | style="border:1pt solid #000000;padding:0.176cm;"| | style="border:1pt solid #000000;padding:0.176cm;"| Let us compile the code.

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

Highlight the makefile

Press Enter | style="border:1pt solid #000000;padding:0.176cm;"| For that, we have to create a Makefile.

Type gedit Makefile

The Makefile is a special file containing shell commands.

Press Enter.

Create a Makefile where you have saved the simple_module dot c .

|- | style="border:1pt solid #000000;padding:0.176cm;"| Copy paste the makefile content | style="border:1pt solid #000000;padding:0.176cm;"| Type the code as shown.

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

Highlight simple_module.o

Highlight all:

Highlight clean:

| style="border:1pt solid #000000;padding:0.176cm;"| The obj hyphen m variable tells the kernel Makefile that this module needs to be compiled.

When you run the make all command, then commands under all section will be executed.

If you run the make clean command, it executes commands under the clean section.

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

Highlight uname -r Highlight (PWD) Highlight M=$(PWD) Highlight modules | style="border:1pt solid #000000;padding:0.176cm;"| Using hyphen C, we are running make command inside the kernel source directory.

As you know, uname hyphen r finds the current Linux kernel version of a system.

PWD means the present working directory.

This option tells the kernel makefile that the source code for the driver is in PWD.

The word modules tell the kernel makefile to build the modules.

But it will not build the complete kernel source code.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight clean | style="border:1pt solid #000000;padding:0.176cm;"| The word clean tells the kernel makefile to clean the generated object files.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Press >> Ctrl + S

Click on the close. | style="border:1pt solid #000000;padding:0.176cm;"| Save the file and close the editor.

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

Type >> make all

Press Enter | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal.

Let us compile the program,

Type make space all.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Type ls and Press Enter

Highlight ls

Show the output

| style="border:1pt solid #000000;padding:0.176cm;"| Now type ls.

This command lists the files in the current directory.

Here, you can see the number of files created in this directory.

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

Highlight mod.c | style="border:1pt solid #000000;padding:0.176cm;"| The module.symvers file contains a list of all symbols

These symbols are exported from the kernel build.

The mod.c file contains information about the module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight mod.o | style="border:1pt solid #000000;padding:0.176cm;"| Mod.o file is object file resulting from the compilation of the mod.c file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight .o | style="border:1pt solid #000000;padding:0.176cm;"| This object file is created from the compilation of the module source file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight modules.order | style="border:1pt solid #000000;padding:0.176cm;"| It will list out the order in which the compilation and creation of the .ko file takes place.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight .ko | style="border:1pt solid #000000;padding:0.176cm;"| This is the final kernel module binary that is loaded into the kernel.

|- | 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 >> modinfo simple_module.ko

Press Enter

Highlight modinfo

Highlight filename

Highlight description

Highlight author, license | style="border:1pt solid #000000;padding:0.176cm;"| Let us see the details of a module.

Type modinfo space simple_module dot ko.

This command displays information about the Linux kernel module.

The filename field contains an absolute path to the .ko kernel object file.

This field displays a short description of a module.

Author field shows author and license field shows the license of the module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight srcversion | style="border:1pt solid #000000;padding:0.176cm;"| The srcversion field contains the source code version used to compile a module.

It is calculated automatically at build time.

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

| style="border:1pt solid #000000;padding:0.176cm;"| The depends field contains all modules on which this module depends.

It is shown empty here as this module does not depend on any other module.

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

| style="border:1pt solid #000000;padding:0.176cm;"| Retpoline field indicates that the module is compiled with retpoline method.

Modules must also be compiled with a retpoline-aware compiler.

Otherwise the kernel can be vulnerable.

Retpoline technique protects the kernel from the hacker’s attacks. |- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight name | style="border:1pt solid #000000;padding:0.176cm;"| The name field contains the name of a module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight vermagic | style="border:1pt solid #000000;padding:0.176cm;"| This field shows the version magic number of a module.

This version magic number is used while loading the kernel module.

The version magic number of module and current kernel version should be the same.

Otherwise it will fail to load in the current kernel. |- | 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.

This command removes all object files that are created after the compilation.

Type ls.

Now there are no object files.

|- | style="border:1pt solid #000000;padding:0.176cm;"| | style="border:0.5pt solid #000000;padding:0.176cm;"| With this, we come to the end of this tutorial. Let us summarize.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Slide 6:

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

  • Implement a simple loadable module.
  • Create a Makefile.
  • Compile a module.

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

Assignment:

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

  1. Open the simple_module.c file
  2. Change the module description using MODULE_DESCRIPTION macro
  3. Run the modinfo command
  4. See the output of description.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Slide 8:

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 9:

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 10:

Forum questions: | style="border:1pt solid #000000;padding:0.176cm;"| * Do you have questions in THIS Spoken Tutorial?

  • Please visit this site
  • Choose the minute and second where you have the question.
  • Explain your question briefly.
  • The Spoken Tutorial project will ensure an answer
  • You will have to register to ask questions

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

Forum for specific questions:

| style="border:1pt solid #000000;padding:0.176cm;"| * The Spoken Tutorial forum is for specific questions on this tutorial.

  • Please do not post unrelated and general questions on them.
  • This will help reduce the clutter.
  • With less clutter, we can use these discussions as instructional material.

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

Forum for specific questions: | style="border:1pt solid #000000;padding:0.176cm;"| * Do you have 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 13:

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 14:

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.

|} 

.

I have given the description as “First Linux kernel module”.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight static int init_func(void)

Highlight return(0)

Highlight module_init() | style="border:1pt solid #000000;padding:0.176cm;"| The init function will execute when a module is loaded into the kernel.

So it is called as an initialization function of a module.

If this function fails then the error will be returned.

It will return 0 to the kernel on successful execution.

Initialization function prints a simple message and return zero.

The module init macro is used to register the init function.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight void exit_func (void)

Highlight module_exit() | style="border:1pt solid #000000;padding:0.176cm;"| The exit function will execute when the module is unloaded from the kernel.

It is mostly used to cleanup the resources acquired by the module

The exit function will undo whatever the init function did.

The module underscore exit macro is used to register the exit function. |- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight printk

Highlight KERN_INFO

Press >> Ctrl + S

Press Enter

Click on close option. | style="border:1pt solid #000000;padding:0.176cm;"| In kernel programming, printk is used as a printing function.

It is similar to printf function in C programming.

Using this function, string data will get loaded in the kernel log buffer.

printk has an optional prefix string, Loglevel such as KERN_INFO.

Loglevel specifies the type of message being sent to the kernel message log.

KERN underscore INFO is used for informational messages.

For more log levels, go through the Additional reading material link of this tutorial.

Press Ctrl + S keys to save the program .

Close the file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal. | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal. |- | style="border:1pt solid #000000;padding:0.176cm;"| | style="border:1pt solid #000000;padding:0.176cm;"| Let us compile the code.

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

Highlight the makefile

Press Enter | style="border:1pt solid #000000;padding:0.176cm;"| For that, we have to create a Makefile.

Type gedit Makefile

The Makefile is a special file containing shell commands.

Press Enter.

Create a Makefile where you have saved the simple_module dot c .

|- | style="border:1pt solid #000000;padding:0.176cm;"| Copy paste the makefile content | style="border:1pt solid #000000;padding:0.176cm;"| Type the code as shown.

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

Highlight simple_module.o

Highlight all:

Highlight clean:

| style="border:1pt solid #000000;padding:0.176cm;"| The obj hyphen m variable tells the kernel Makefile that this module needs to be compiled.

When you run the make all command, then commands under all section will be executed.

If you run the make clean command, it executes commands under the clean section.

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

Highlight uname -r Highlight (PWD) Highlight M=$(PWD) Highlight modules | style="border:1pt solid #000000;padding:0.176cm;"| Using hyphen C, we are running make command inside the kernel source directory.

As you know, uname hyphen r finds the current Linux kernel version of a system.

PWD means the present working directory.

This option tells the kernel makefile that the source code for the driver is in PWD.

The word modules tell the kernel makefile to build the modules.

But it will not build the complete kernel source code.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight clean | style="border:1pt solid #000000;padding:0.176cm;"| The word clean tells the kernel makefile to clean the generated object files.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Press >> Ctrl + S

Click on the close. | style="border:1pt solid #000000;padding:0.176cm;"| Save the file and close the editor.

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

Type >> make all

Press Enter | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal.

Let us compile the program,

Type make space all.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Type ls and Press Enter

Highlight ls

Show the output

| style="border:1pt solid #000000;padding:0.176cm;"| Now type ls.

This command lists the files in the current directory.

Here, you can see the number of files created in this directory.

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

Highlight mod.c | style="border:1pt solid #000000;padding:0.176cm;"| The module.symvers file contains a list of all symbols

These symbols are exported from the kernel build.

The mod.c file contains information about the module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight mod.o | style="border:1pt solid #000000;padding:0.176cm;"| Mod.o file is object file resulting from the compilation of the mod.c file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight .o | style="border:1pt solid #000000;padding:0.176cm;"| This object file is created from the compilation of the module source file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight modules.order | style="border:1pt solid #000000;padding:0.176cm;"| It will list out the order in which the compilation and creation of the .ko file takes place.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight .ko | style="border:1pt solid #000000;padding:0.176cm;"| This is the final kernel module binary that is loaded into the kernel.

|- | 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 >> modinfo simple_module.ko

Press Enter

Highlight modinfo

Highlight filename

Highlight description

Highlight author, license | style="border:1pt solid #000000;padding:0.176cm;"| Let us see the details of a module.

Type modinfo space simple_module dot ko.

This command displays information about the Linux kernel module.

The filename field contains an absolute path to the .ko kernel object file.

This field displays a short description of a module.

Author field shows author and license field shows the license of the module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight srcversion | style="border:1pt solid #000000;padding:0.176cm;"| The srcversion field contains the source code version used to compile a module.

It is calculated automatically at build time.

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

| style="border:1pt solid #000000;padding:0.176cm;"| The depends field contains all modules on which this module depends.

It is shown empty here as this module does not depend on any other module.

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

| style="border:1pt solid #000000;padding:0.176cm;"| Retpoline field indicates that the module is compiled with retpoline method.

Modules must also be compiled with a retpoline-aware compiler.

Otherwise the kernel can be vulnerable.

Retpoline technique protects the kernel from the hacker’s attacks. |- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight name | style="border:1pt solid #000000;padding:0.176cm;"| The name field contains the name of a module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight vermagic | style="border:1pt solid #000000;padding:0.176cm;"| This field shows the version magic number of a module.

This version magic number is used while loading the kernel module.

The version magic number of module and current kernel version should be the same.

Otherwise it will fail to load in the current kernel. |- | 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.

This command removes all object files that are created after the compilation.

Type ls.

Now there are no object files.

|- | style="border:1pt solid #000000;padding:0.176cm;"| | style="border:0.5pt solid #000000;padding:0.176cm;"| With this, we come to the end of this tutorial. Let us summarize.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Slide 6:

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

  • Implement a simple loadable module.
  • Create a Makefile.
  • Compile a module.

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

Assignment:

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

  1. Open the simple_module.c file
  2. Change the module description using MODULE_DESCRIPTION macro
  3. Run the modinfo command
  4. See the output of description.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Slide 8:

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 9:

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 10:

Forum questions: | style="border:1pt solid #000000;padding:0.176cm;"| * Do you have questions in THIS Spoken Tutorial?

  • Please visit this site
  • Choose the minute and second where you have the question.
  • Explain your question briefly.
  • The Spoken Tutorial project will ensure an answer
  • You will have to register to ask questions

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

Forum for specific questions:

| style="border:1pt solid #000000;padding:0.176cm;"| * The Spoken Tutorial forum is for specific questions on this tutorial.

  • Please do not post unrelated and general questions on them.
  • This will help reduce the clutter.
  • With less clutter, we can use these discussions as instructional material.

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

Forum for specific questions: | style="border:1pt solid #000000;padding:0.176cm;"| * Do you have 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 13:

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 14:

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. .

I have given the description as “First Linux kernel module”.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight static int init_func(void)

Highlight return(0)

Highlight module_init() | style="border:1pt solid #000000;padding:0.176cm;"| The init function will execute when a module is loaded into the kernel.

So it is called as an initialization function of a module.

If this function fails then the error will be returned.

It will return 0 to the kernel on successful execution.

Initialization function prints a simple message and return zero.

The module init macro is used to register the init function.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight void exit_func (void)

Highlight module_exit() | style="border:1pt solid #000000;padding:0.176cm;"| The exit function will execute when the module is unloaded from the kernel.

It is mostly used to cleanup the resources acquired by the module

The exit function will undo whatever the init function did.

The module underscore exit macro is used to register the exit function. |- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight printk

Highlight KERN_INFO

Press >> Ctrl + S

Press Enter

Click on close option. | style="border:1pt solid #000000;padding:0.176cm;"| In kernel programming, printk is used as a printing function.

It is similar to printf function in C programming.

Using this function, string data will get loaded in the kernel log buffer.

printk has an optional prefix string, Loglevel such as KERN_INFO.

Loglevel specifies the type of message being sent to the kernel message log.

KERN underscore INFO is used for informational messages.

For more log levels, go through the Additional reading material link of this tutorial.

Press Ctrl + S keys to save the program .

Close the file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal. | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal. |- | style="border:1pt solid #000000;padding:0.176cm;"| | style="border:1pt solid #000000;padding:0.176cm;"| Let us compile the code.

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

Highlight the makefile

Press Enter | style="border:1pt solid #000000;padding:0.176cm;"| For that, we have to create a Makefile.

Type gedit Makefile

The Makefile is a special file containing shell commands.

Press Enter.

Create a Makefile where you have saved the simple_module dot c .

|- | style="border:1pt solid #000000;padding:0.176cm;"| Copy paste the makefile content | style="border:1pt solid #000000;padding:0.176cm;"| Type the code as shown.

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

Highlight simple_module.o

Highlight all:

Highlight clean:

| style="border:1pt solid #000000;padding:0.176cm;"| The obj hyphen m variable tells the kernel Makefile that this module needs to be compiled.

When you run the make all command, then commands under all section will be executed.

If you run the make clean command, it executes commands under the clean section.

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

Highlight uname -r Highlight (PWD) Highlight M=$(PWD) Highlight modules | style="border:1pt solid #000000;padding:0.176cm;"| Using hyphen C, we are running make command inside the kernel source directory.

As you know, uname hyphen r finds the current Linux kernel version of a system.

PWD means the present working directory.

This option tells the kernel makefile that the source code for the driver is in PWD.

The word modules tell the kernel makefile to build the modules.

But it will not build the complete kernel source code.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight clean | style="border:1pt solid #000000;padding:0.176cm;"| The word clean tells the kernel makefile to clean the generated object files.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Press >> Ctrl + S

Click on the close. | style="border:1pt solid #000000;padding:0.176cm;"| Save the file and close the editor.

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

Type >> make all

Press Enter | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal.

Let us compile the program,

Type make space all.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Type ls and Press Enter

Highlight ls

Show the output

| style="border:1pt solid #000000;padding:0.176cm;"| Now type ls.

This command lists the files in the current directory.

Here, you can see the number of files created in this directory.

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

Highlight mod.c | style="border:1pt solid #000000;padding:0.176cm;"| The module.symvers file contains a list of all symbols

These symbols are exported from the kernel build.

The mod.c file contains information about the module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight mod.o | style="border:1pt solid #000000;padding:0.176cm;"| Mod.o file is object file resulting from the compilation of the mod.c file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight .o | style="border:1pt solid #000000;padding:0.176cm;"| This object file is created from the compilation of the module source file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight modules.order | style="border:1pt solid #000000;padding:0.176cm;"| It will list out the order in which the compilation and creation of the .ko file takes place.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight .ko | style="border:1pt solid #000000;padding:0.176cm;"| This is the final kernel module binary that is loaded into the kernel.

|- | 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 >> modinfo simple_module.ko

Press Enter

Highlight modinfo

Highlight filename

Highlight description

Highlight author, license | style="border:1pt solid #000000;padding:0.176cm;"| Let us see the details of a module.

Type modinfo space simple_module dot ko.

This command displays information about the Linux kernel module.

The filename field contains an absolute path to the .ko kernel object file.

This field displays a short description of a module.

Author field shows author and license field shows the license of the module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight srcversion | style="border:1pt solid #000000;padding:0.176cm;"| The srcversion field contains the source code version used to compile a module.

It is calculated automatically at build time.

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

| style="border:1pt solid #000000;padding:0.176cm;"| The depends field contains all modules on which this module depends.

It is shown empty here as this module does not depend on any other module.

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

| style="border:1pt solid #000000;padding:0.176cm;"| Retpoline field indicates that the module is compiled with retpoline method.

Modules must also be compiled with a retpoline-aware compiler.

Otherwise the kernel can be vulnerable.

Retpoline technique protects the kernel from the hacker’s attacks. |- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight name | style="border:1pt solid #000000;padding:0.176cm;"| The name field contains the name of a module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight vermagic | style="border:1pt solid #000000;padding:0.176cm;"| This field shows the version magic number of a module.

This version magic number is used while loading the kernel module.

The version magic number of module and current kernel version should be the same.

Otherwise it will fail to load in the current kernel. |- | 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.

This command removes all object files that are created after the compilation.

Type ls.

Now there are no object files.

|- | style="border:1pt solid #000000;padding:0.176cm;"| | style="border:0.5pt solid #000000;padding:0.176cm;"| With this, we come to the end of this tutorial. Let us summarize.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Slide 6:

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

  • Implement a simple loadable module.
  • Create a Makefile.
  • Compile a module.

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

Assignment:

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

  1. Open the simple_module.c file
  2. Change the module description using MODULE_DESCRIPTION macro
  3. Run the modinfo command
  4. See the output of description.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Slide 8:

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 9:

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 10:

Forum questions: | style="border:1pt solid #000000;padding:0.176cm;"| * Do you have questions in THIS Spoken Tutorial?

  • Please visit this site
  • Choose the minute and second where you have the question.
  • Explain your question briefly.
  • The Spoken Tutorial project will ensure an answer
  • You will have to register to ask questions

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

Forum for specific questions:

| style="border:1pt solid #000000;padding:0.176cm;"| * The Spoken Tutorial forum is for specific questions on this tutorial.

  • Please do not post unrelated and general questions on them.
  • This will help reduce the clutter.
  • With less clutter, we can use these discussions as instructional material.

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

Forum for specific questions: | style="border:1pt solid #000000;padding:0.176cm;"| * Do you have 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 13:

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 14:

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.

|}


|}

| style="border:1pt solid #000000;padding:0.176cm;"| Highlight static int init_func(void)

Highlight return(0)

Highlight module_init() | style="border:1pt solid #000000;padding:0.176cm;"| The init function will execute when a module is loaded into the kernel.

So it is called as an initialization function of a module.

If this function fails then the error will be returned. .

I have given the description as “First Linux kernel module”.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight static int init_func(void)

Highlight return(0)

Highlight module_init() | style="border:1pt solid #000000;padding:0.176cm;"| The init function will execute when a module is loaded into the kernel.

So it is called as an initialization function of a module.

If this function fails then the error will be returned.

It will return 0 to the kernel on successful execution.

Initialization function prints a simple message and return zero.

The module init macro is used to register the init function.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight void exit_func (void)

Highlight module_exit() | style="border:1pt solid #000000;padding:0.176cm;"| The exit function will execute when the module is unloaded from the kernel.

It is mostly used to cleanup the resources acquired by the module

The exit function will undo whatever the init function did.

The module underscore exit macro is used to register the exit function. |- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight printk

Highlight KERN_INFO

Press >> Ctrl + S

Press Enter

Click on close option. | style="border:1pt solid #000000;padding:0.176cm;"| In kernel programming, printk is used as a printing function.

It is similar to printf function in C programming.

Using this function, string data will get loaded in the kernel log buffer.

printk has an optional prefix string, Loglevel such as KERN_INFO.

Loglevel specifies the type of message being sent to the kernel message log.

KERN underscore INFO is used for informational messages.

For more log levels, go through the Additional reading material link of this tutorial.

Press Ctrl + S keys to save the program .

Close the file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal. | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal. |- | style="border:1pt solid #000000;padding:0.176cm;"| | style="border:1pt solid #000000;padding:0.176cm;"| Let us compile the code.

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

Highlight the makefile

Press Enter | style="border:1pt solid #000000;padding:0.176cm;"| For that, we have to create a Makefile.

Type gedit Makefile

The Makefile is a special file containing shell commands.

Press Enter.

Create a Makefile where you have saved the simple_module dot c .

|- | style="border:1pt solid #000000;padding:0.176cm;"| Copy paste the makefile content | style="border:1pt solid #000000;padding:0.176cm;"| Type the code as shown.

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

Highlight simple_module.o

Highlight all:

Highlight clean:

| style="border:1pt solid #000000;padding:0.176cm;"| The obj hyphen m variable tells the kernel Makefile that this module needs to be compiled.

When you run the make all command, then commands under all section will be executed.

If you run the make clean command, it executes commands under the clean section.

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

Highlight uname -r Highlight (PWD) Highlight M=$(PWD) Highlight modules | style="border:1pt solid #000000;padding:0.176cm;"| Using hyphen C, we are running make command inside the kernel source directory.

As you know, uname hyphen r finds the current Linux kernel version of a system.

PWD means the present working directory.

This option tells the kernel makefile that the source code for the driver is in PWD.

The word modules tell the kernel makefile to build the modules.

But it will not build the complete kernel source code.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight clean | style="border:1pt solid #000000;padding:0.176cm;"| The word clean tells the kernel makefile to clean the generated object files.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Press >> Ctrl + S

Click on the close. | style="border:1pt solid #000000;padding:0.176cm;"| Save the file and close the editor.

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

Type >> make all

Press Enter | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal.

Let us compile the program,

Type make space all.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Type ls and Press Enter

Highlight ls

Show the output

| style="border:1pt solid #000000;padding:0.176cm;"| Now type ls.

This command lists the files in the current directory.

Here, you can see the number of files created in this directory.

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

Highlight mod.c | style="border:1pt solid #000000;padding:0.176cm;"| The module.symvers file contains a list of all symbols

These symbols are exported from the kernel build.

The mod.c file contains information about the module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight mod.o | style="border:1pt solid #000000;padding:0.176cm;"| Mod.o file is object file resulting from the compilation of the mod.c file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight .o | style="border:1pt solid #000000;padding:0.176cm;"| This object file is created from the compilation of the module source file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight modules.order | style="border:1pt solid #000000;padding:0.176cm;"| It will list out the order in which the compilation and creation of the .ko file takes place.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight .ko | style="border:1pt solid #000000;padding:0.176cm;"| This is the final kernel module binary that is loaded into the kernel.

|- | 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 >> modinfo simple_module.ko

Press Enter

Highlight modinfo

Highlight filename

Highlight description

Highlight author, license | style="border:1pt solid #000000;padding:0.176cm;"| Let us see the details of a module.

Type modinfo space simple_module dot ko.

This command displays information about the Linux kernel module.

The filename field contains an absolute path to the .ko kernel object file.

This field displays a short description of a module.

Author field shows author and license field shows the license of the module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight srcversion | style="border:1pt solid #000000;padding:0.176cm;"| The srcversion field contains the source code version used to compile a module.

It is calculated automatically at build time.

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

| style="border:1pt solid #000000;padding:0.176cm;"| The depends field contains all modules on which this module depends.

It is shown empty here as this module does not depend on any other module.

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

| style="border:1pt solid #000000;padding:0.176cm;"| Retpoline field indicates that the module is compiled with retpoline method.

Modules must also be compiled with a retpoline-aware compiler.

Otherwise the kernel can be vulnerable.

Retpoline technique protects the kernel from the hacker’s attacks. |- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight name | style="border:1pt solid #000000;padding:0.176cm;"| The name field contains the name of a module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight vermagic | style="border:1pt solid #000000;padding:0.176cm;"| This field shows the version magic number of a module.

This version magic number is used while loading the kernel module.

The version magic number of module and current kernel version should be the same.

Otherwise it will fail to load in the current kernel. |- | 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.

This command removes all object files that are created after the compilation.

Type ls.

Now there are no object files.

|- | style="border:1pt solid #000000;padding:0.176cm;"| | style="border:0.5pt solid #000000;padding:0.176cm;"| With this, we come to the end of this tutorial. Let us summarize.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Slide 6:

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

  • Implement a simple loadable module.
  • Create a Makefile.
  • Compile a module.

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

Assignment:

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

  1. Open the simple_module.c file
  2. Change the module description using MODULE_DESCRIPTION macro
  3. Run the modinfo command
  4. See the output of description.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Slide 8:

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 9:

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 10:

Forum questions: | style="border:1pt solid #000000;padding:0.176cm;"| * Do you have questions in THIS Spoken Tutorial?

  • Please visit this site
  • Choose the minute and second where you have the question.
  • Explain your question briefly.
  • The Spoken Tutorial project will ensure an answer
  • You will have to register to ask questions

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

Forum for specific questions:

| style="border:1pt solid #000000;padding:0.176cm;"| * The Spoken Tutorial forum is for specific questions on this tutorial.

  • Please do not post unrelated and general questions on them.
  • This will help reduce the clutter.
  • With less clutter, we can use these discussions as instructional material.

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

Forum for specific questions: | style="border:1pt solid #000000;padding:0.176cm;"| * Do you have 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 13:

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 14:

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.

|}


It will return 0 to the kernel on successful execution.

Initialization function prints a simple message and return zero.

The module init macro is used to register the init function.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight void exit_func (void)

Highlight module_exit() | style="border:1pt solid #000000;padding:0.176cm;"| The exit function will execute when the module is unloaded from the kernel.

It is mostly used to cleanup the resources acquired by the module

The exit function will undo whatever the init function did.

The module underscore exit macro is used to register the exit function. |- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight printk

Highlight KERN_INFO

Press >> Ctrl + S

Press Enter

Click on close option. | style="border:1pt solid #000000;padding:0.176cm;"| In kernel programming, printk is used as a printing function.

It is similar to printf function in C programming.

Using this function, string data will get loaded in the kernel log buffer.

printk has an optional prefix string, Loglevel such as KERN_INFO.

Loglevel specifies the type of message being sent to the kernel message log.

KERN underscore INFO is used for informational messages.

For more log levels, go through the Additional reading material link of this tutorial.

Press Ctrl + S keys to save the program .

Close the file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal. | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal. |- | style="border:1pt solid #000000;padding:0.176cm;"| | style="border:1pt solid #000000;padding:0.176cm;"| Let us compile the code.

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

Highlight the makefile

Press Enter | style="border:1pt solid #000000;padding:0.176cm;"| For that, we have to create a Makefile.

Type gedit Makefile

The Makefile is a special file containing shell commands.

Press Enter.

Create a Makefile where you have saved the simple_module dot c .

|- | style="border:1pt solid #000000;padding:0.176cm;"| Copy paste the makefile content | style="border:1pt solid #000000;padding:0.176cm;"| Type the code as shown.

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

Highlight simple_module.o

Highlight all:

Highlight clean:

| style="border:1pt solid #000000;padding:0.176cm;"| The obj hyphen m variable tells the kernel Makefile that this module needs to be compiled.

When you run the make all command, then commands under all section will be executed.

If you run the make clean command, it executes commands under the clean section.

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

Highlight uname -r Highlight (PWD) Highlight M=$(PWD) Highlight modules | style="border:1pt solid #000000;padding:0.176cm;"| Using hyphen C, we are running make command inside the kernel source directory.

As you know, uname hyphen r finds the current Linux kernel version of a system.

PWD means the present working directory.

This option tells the kernel makefile that the source code for the driver is in PWD.

The word modules tell the kernel makefile to build the modules.

But it will not build the complete kernel source code.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight clean | style="border:1pt solid #000000;padding:0.176cm;"| The word clean tells the kernel makefile to clean the generated object files.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Press >> Ctrl + S

Click on the close. | style="border:1pt solid #000000;padding:0.176cm;"| Save the file and close the editor.

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

Type >> make all

Press Enter | style="border:1pt solid #000000;padding:0.176cm;"| Switch back to the terminal.

Let us compile the program,

Type make space all.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Type ls and Press Enter

Highlight ls

Show the output

| style="border:1pt solid #000000;padding:0.176cm;"| Now type ls.

This command lists the files in the current directory.

Here, you can see the number of files created in this directory.

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

Highlight mod.c | style="border:1pt solid #000000;padding:0.176cm;"| The module.symvers file contains a list of all symbols

These symbols are exported from the kernel build.

The mod.c file contains information about the module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight mod.o | style="border:1pt solid #000000;padding:0.176cm;"| Mod.o file is object file resulting from the compilation of the mod.c file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight .o | style="border:1pt solid #000000;padding:0.176cm;"| This object file is created from the compilation of the module source file.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight modules.order | style="border:1pt solid #000000;padding:0.176cm;"| It will list out the order in which the compilation and creation of the .ko file takes place.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight .ko | style="border:1pt solid #000000;padding:0.176cm;"| This is the final kernel module binary that is loaded into the kernel.

|- | 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 >> modinfo simple_module.ko

Press Enter

Highlight modinfo

Highlight filename

Highlight description

Highlight author, license | style="border:1pt solid #000000;padding:0.176cm;"| Let us see the details of a module.

Type modinfo space simple_module dot ko.

This command displays information about the Linux kernel module.

The filename field contains an absolute path to the .ko kernel object file.

This field displays a short description of a module.

Author field shows author and license field shows the license of the module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight srcversion | style="border:1pt solid #000000;padding:0.176cm;"| The srcversion field contains the source code version used to compile a module.

It is calculated automatically at build time.

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

| style="border:1pt solid #000000;padding:0.176cm;"| The depends field contains all modules on which this module depends.

It is shown empty here as this module does not depend on any other module.

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

| style="border:1pt solid #000000;padding:0.176cm;"| Retpoline field indicates that the module is compiled with retpoline method.

Modules must also be compiled with a retpoline-aware compiler.

Otherwise the kernel can be vulnerable.

Retpoline technique protects the kernel from the hacker’s attacks. |- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight name | style="border:1pt solid #000000;padding:0.176cm;"| The name field contains the name of a module.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Highlight vermagic | style="border:1pt solid #000000;padding:0.176cm;"| This field shows the version magic number of a module.

This version magic number is used while loading the kernel module.

The version magic number of module and current kernel version should be the same.

Otherwise it will fail to load in the current kernel. |- | 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.

This command removes all object files that are created after the compilation.

Type ls.

Now there are no object files.

|- | style="border:1pt solid #000000;padding:0.176cm;"| | style="border:0.5pt solid #000000;padding:0.176cm;"| With this, we come to the end of this tutorial. Let us summarize.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Slide 6:

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

  • Implement a simple loadable module.
  • Create a Makefile.
  • Compile a module.

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

Assignment:

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

  1. Open the simple_module.c file
  2. Change the module description using MODULE_DESCRIPTION macro
  3. Run the modinfo command
  4. See the output of description.

|- | style="border:1pt solid #000000;padding:0.176cm;"| Slide 8:

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 9:

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 10:

Forum questions: | style="border:1pt solid #000000;padding:0.176cm;"| * Do you have questions in THIS Spoken Tutorial?

  • Please visit this site
  • Choose the minute and second where you have the question.
  • Explain your question briefly.
  • The Spoken Tutorial project will ensure an answer
  • You will have to register to ask questions

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

Forum for specific questions:

| style="border:1pt solid #000000;padding:0.176cm;"| * The Spoken Tutorial forum is for specific questions on this tutorial.

  • Please do not post unrelated and general questions on them.
  • This will help reduce the clutter.
  • With less clutter, we can use these discussions as instructional material.

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

Forum for specific questions: | style="border:1pt solid #000000;padding:0.176cm;"| * Do you have 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 13:

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 14:

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.

|}

Contributors and Content Editors

Nancyvarkey, Nirmala Venkat

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