Nancyvarkey at 08:21, 15 October 2020

2020-10-15T08:21:36Z

Nancyvarkey at 10:08, 28 September 2020

2020-09-28T10:08:45Z

Nirmala Venkat: Created page with " {| style="border-spacing:0;" | style="border:1pt solid #000000;padding:0.176cm;"| '''Visual cue :''' | style="border:1pt solid #000000;padding:0.176cm;"| '''Narration :''' |..."

2020-09-22T11:36:17Z

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

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

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 1 :
| style="border:1pt solid #000000;padding:0.176cm;"| Welcome to the spoken tutorial on '''File Operations on a Device.'''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 2 :
Learning objectives:
| style="border:1pt solid #000000;padding:0.176cm;"| In this tutorial, we will learn how to

* Implement the basic''' file operations '''such as '''open() '''and''' close()''' on a '''device'''.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 3:

System Requirements:
| style="border:1pt solid #000000;padding:0.176cm;"| To record this tutorial, I am using,

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

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

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

If not, then go through the '''C/C++''' and '''Linux''' spoken tutorials on this website.
|-
| style="border:1pt solid #000000;padding:0.176cm;"| Point to the '''folder''' and''' file''' in '''desktop'''

Point to the '''files.'''
| style="border:1pt solid #000000;padding:0.176cm;"| Go to the '''DeviceDriver '''folder on the desktop.

Here I have created a new directory''' '''as '''FileOperations.'''

In this directory, I have saved a '''simple_driver dot c driver file, Makefile and user.c.'''

I’ll use these files''' '''for demonstration.

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

'''Code files:'''
| style="border:1pt solid #000000;padding:0.176cm;"| * The files used in this tutorial are available in the '''Code Files '''link on this tutorial page.
* Please download and extract them
* Make a copy and then use them while practising

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

About new_device
| style="border:1pt solid #000000;padding:0.176cm;"| We have already registered and created a device called '''new_device '''in the earlier tutorial.

In this tutorial, we will perform file operations such as '''open''' and '''close''' on''' new_device.'''

We will use a user program called '''user.c '''to access this device.

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

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

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''cd Desktop/DeviceDriver/FileOperations'''
| style="border:1pt solid #000000;padding:0.176cm;"| Go to the directory '''FileOperations '''as shown here.

Press '''Enter '''key after every command'''.'''
|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''gedit simple_driver.c'''

| style="border:1pt solid #000000;padding:0.176cm;"| Type''' gedit space simple_driver dot c.'''

I have used the same''' '''file''' simple_driver dot c '''which we used earlier.

Here, I have implemented the basic file functions for the device '''new_device.'''

Using these''' '''functions users can perform the '''open '''and '''close''' '''operations '''on a '''device'''.
|-
| style="border:1pt solid #000000;padding:0.176cm;"|
| style="border:1pt solid #000000;padding:0.176cm;"| Let me explain the code.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''<nowiki>#include<linux/fs.h></nowiki>''' and

'''<nowiki>#include<linux/cdev.h></nowiki>'''

Highlight '''cdev.h'''

Highlight '''struct cdev.'''
| style="border:1pt solid #000000;padding:0.176cm;"| We have to include these '''header files '''to perform file''' '''related operations.

The''' cdev dot h header '''file is used to create the''' character device structure.'''

The '''cdev structure''' is used to describe '''character devices''' in the''' Linux kernel.'''

Here,''' my_cdev''' represents our '''device cdev structure''' in the '''kernel. '''

|-
| style="border:1pt solid #000000;padding:0.176cm;"|
| style="border:1pt solid #000000;padding:0.176cm;"| Now let us see how to implement the '''device file operations.'''

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

'''struct file_operations structure'''
| style="border:1pt solid #000000;padding:0.176cm;"| * '''File operations''' are defined in the''' kernel''' as the instance of '''struct file_operation.'''
* This is the most important structure of a driver defined in the '''fs dot h file.'''
* Each field of this '''structure '''is a '''function pointer.'''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' struct file_operations structure'''

Highlight '''mydevice_open '''and '''mydevice_release'''
| style="border:1pt solid #000000;padding:0.176cm;"| Here, I have defined the''' file_operations structure '''for our '''device.'''

We will implement two functions''' mydevice_open '''and''' mydevice_release '''in a driver.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' function declarations.'''
| style="border:1pt solid #000000;padding:0.176cm;"| You have to declare the prototypes of these '''functions '''at the start of the '''driver.'''

You can get these '''functions '''declarations from the '''fs dot h header file'''.
|-
| style="border:1pt solid #000000;padding:0.176cm;"|
| style="border:1pt solid #000000;padding:0.176cm;"| Now let us see the''' kernels functions''' used to implement the file operations.

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

Highlight''' cdev'''

Highlight '''fops'''
| style="border:1pt solid #000000;padding:0.176cm;"| The '''cdev_init() function''' is used to initialize the members of the '''cdev structure.'''

'''cdev''' specifies a''' '''pointer to the''' cdev structure''' to initialize.

'''fops''' specifies a''' '''pointer to device '''file operation structure.'''

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

Highlight '''cdev_init(&my_cdev, &fops)'''

Highlight '''my_cdev''' and '''fops.'''
| style="border:1pt solid #000000;padding:0.176cm;"| In the '''init_function''', we have already created a device '''new_device '''and its '''class.'''

After that we have to initialize the '''cdev structure '''of a device as shown here.

It will establish a connection between '''cdev structure '''and '''file_operations.'''
|-
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''int cdev_add()'''

Highlight''' p'''
Highlight '''dev'''
Highlight '''count'''
| style="border:1pt solid #000000;padding:0.176cm;"| '''cdev_add()''' adds a '''cdev''' to the system to complete the registration of a device.

It returns a negative error code on failure.

'''p '''specifies the cdev structure for the device.

'''dev''' specifies a device number.

'''count '''specifies''' '''a number of consecutive minor numbers corresponding to this device.

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

Highlight my_cdev

Highlight the''' device_destroy(cl,device_num),'''

'''class_destroy(cl), unregister_chrdev_region(device_num,1);'''

Highlight''' printk'''
| style="border:1pt solid #000000;padding:0.176cm;"| I used this '''function''' to add the '''cdev structure''' of '''new_device '''as shown here.

If the registration fails then we have to destroy a '''device''' and its '''class. '''

Also unregister the device from the system as shown here.

This '''printk''' message will show the successful execution of the '''cdev_add()''' '''function'''.

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

Highlight '''printk''' message
| style="border:1pt solid #000000;padding:0.176cm;"| Now we will learn how to implement the''' device file '''functions'''.'''

Here, I have defined the '''open''' function with a '''printk''' message.

'''mydevice_open() '''function gets executed when the user program opens the device.

This''' printk''' message will display in the '''kernel log level.'''

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

Highlight '''printk message'''

| style="border:1pt solid #000000;padding:0.176cm;"| Similarly, I have defined the '''release '''function with a '''printk''' message.

'''mydevice_release() function''' gets executed when the '''user''' '''program''' closes the device.

This '''printk''' message will display in the''' kernel log level'''.

|-
| style="border:1pt solid #000000;padding:0.176cm;"|
| style="border:1pt solid #000000;padding:0.176cm;"| Let us see the '''exit function '''of a driver.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| '''void cdev_del (struct cdev * cdev)'''

Highlight''' cdev'''
| style="border:1pt solid #000000;padding:0.176cm;"| '''cdev_del() function''' will remove a''' cdev structure '''of a '''device '''from the kernel.

'''cdev '''specifies the '''cdev''' structure to be removed.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight '''cdev_del()'''
| style="border:1pt solid #000000;padding:0.176cm;"| Here, we remove the '''cdev structure '''of a '''new_device '''before removing its''' '''file'''.'''

|-
| style="border:1pt solid #000000;padding:0.176cm;"|
| style="border:1pt solid #000000;padding:0.176cm;"| Now let us write the program to perform the file operations on the '''device file.'''

Save and close the file.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''gedit user.c.'''

| style="border:1pt solid #000000;padding:0.176cm;"| Type '''gedit user dot c.'''

Here, I have created a simple''' user program''' which will open and close the '''device.'''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Highlight''' open() function'''

Highlight '''printf'''

Highlight '''close() function'''

| style="border:1pt solid #000000;padding:0.176cm;"| The '''open() system call '''will internally call the''' open function''' of '''new_device '''from its driver.

'''printf function''' will print the message if the '''open function''' fails to open the '''new_device.'''

'''close() system call''' will internally call the '''close function '''of a''' new_device''' from its driver.

Save and close the''' '''file'''.'''

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

Save the''' Makefile '''
| style="border:1pt solid #000000;padding:0.176cm;"| Let us create a '''Makefile''' to '''compile''' a '''driver.'''

Type''' gedit space Makefile.'''

Type this '''code''' in a '''Makefile '''or you can use the downloaded '''Makefile.'''

Save and close the file.

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

Type >> '''make all'''

| style="border:1pt solid #000000;padding:0.176cm;"| Let us '''compile''' the '''driver.'''
Type''' sudo su '''and''' password''' to be a superuser.
Type '''make space all.'''

Clear the screen.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >>''' insmod simple_driver.ko'''
| style="border:1pt solid #000000;padding:0.176cm;"| Now let us load the '''driver '''into the''' kernel.'''

For that, type '''insmod space simple_driver dot ko.'''

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

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

Highlight the output
| style="border:1pt solid #000000;padding:0.176cm;"| Let us see the loaded '''printk '''messages from the '''initialisation function.'''

Type '''dmesg space pipe space grep space simple_driver.'''

Here, you can see the''' cdev structure''' of a '''new_device '''registered successfully.
|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >>''' clear'''
| style="border:1pt solid #000000;padding:0.176cm;"| Clear the screen'''.'''

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''gcc -c user. c'''

Type >>''' gcc -o user user.o.'''

Type >>''' ./user'''

Highlight output
| style="border:1pt solid #000000;padding:0.176cm;"| Now let us compile the '''user.c file'''

Type '''gcc space hyphen c space user dot c'''

Then type''' gcc space hyphen o space user space user dot o'''

Now to execute the program type '''dot slash user.'''

Here, it indicates that the '''new_device '''opened successfully.
|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >>''' clear'''
| style="border:1pt solid #000000;padding:0.176cm;"| Clear the screen'''.'''

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

Highlight the '''respective messages'''

Type >>''' clear'''
| style="border:1pt solid #000000;padding:0.176cm;"| Type the command as shown here.

The output shows that '''open '''and''' close''' '''functions '''of the driver are executed successfully.

It indicates that the '''new_device''' is opened and closed by the '''user program.'''

Clear the '''screen.'''

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

Type '''dmesg | grep simple_driver'''

Highlight the '''output'''

Type >>''' clear'''
| style="border:1pt solid #000000;padding:0.176cm;"| Now let us unload the '''driver.'''

Type '''rmmod space simple_driver dot ko'''

To see the unloaded '''printk '''messages type this '''dmesg '''command.

It indicates that the''' cdev structure '''of a '''new_device '''removed from the '''kernel. '''

Clear the screen.

|-
| style="border:1pt solid #000000;padding:0.176cm;"| Type >> '''make clean'''
| style="border:1pt solid #000000;padding:0.176cm;"| Let us remove the '''object files''' created after the compilation'''.'''

Type '''make space clean.'''

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

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

* Implement the basic''' file operations '''such as '''open() '''and''' close''' on a device.

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

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

# Open the '''simple driver.c file.'''
# Write the different '''printk''' messages in the open and close functions.
# Compile and load the''' driver.'''
# Compile and execute the''' user program.'''
# Use '''dmesg command '''to check whether the device is opened or not.
# Unload the driver from the''' kernel.'''
|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 9 :

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 10:

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 11:

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

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

Forum for specific questions:
| style="border:1pt solid #000000;padding:0.176cm;"| * Do you have any general or technical questions on Embedded Linux Device Driver?
* Please visit the FOSSEE forum and post your question.
|-
| style="border:1pt solid #000000;padding:0.176cm;"| Slide 13 :

Acknowledgment:
| style="border:1pt solid #000000;padding:0.176cm;"| The 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.

|}

Embedded-Linux-Device-Driver/C3/File-Operations-on-a-Device/English - Revision history

Nancyvarkey at 08:21, 15 October 2020

Nancyvarkey at 10:08, 28 September 2020

Nirmala Venkat: Created page with " {| style="border-spacing:0;" | style="border:1pt solid #000000;padding:0.176cm;"| '''Visual cue :''' | style="border:1pt solid #000000;padding:0.176cm;"| '''Narration :''' |..."