Difference between revisions of "Embedded-Linux-Device-Driver/C3/Input-and-Output-Control/English"

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(Created page with " {| border="1" |- | align=center| '''Visual Cue''' | align=center| '''Narration''' |- || Slide 1: Welcome slide: | | Welcome to the spoken tutorial on''' Input and Output Co...")
 
 
Line 13: Line 13:
  
 
Learning objectives:
 
Learning objectives:
−
|| In this tutorial, we will learn about* '''Ioctl''' function''' '''and
+
|| In this tutorial, we will learn about
−
* Data transfer between userspace and kernel space using '''ioctl''' function
+
* '''Ioctl function''' and
 +
* '''Data transfer''' between '''userspace''' and '''kernel space''' using '''ioctl function'''
 
|-  
 
|-  
 
|| Slide 3 :
 
|| Slide 3 :
  
 
System Requirements:
 
System Requirements:
−
|| To record this tutorial, I am using,* VirtualBox 5.2.
+
|| To record this tutorial, I am using,
−
* Ubuntu Linux 18.04 LTS operating system.
+
* '''VirtualBox''' 5.2.
−
* Linux kernel version 5.0.0-31 generic.
+
* '''Ubuntu Linux''' 18.04 '''LTS''' operating system.
−
* gedit text editor.
+
* '''Linux kernel''' version 5.0.0-31 generic.
 +
* '''gedit text editor.'''
 
|-  
 
|-  
 
|| Slide 4:
 
|| Slide 4:
  
 
Prerequisites:
 
Prerequisites:
−
|| To follow this tutorial, you should be familiar with:* C programming language  
+
|| To follow this tutorial, you should be familiar with:
−
* Basics of Linux kernel
+
* '''C programming language'''
 +
* Basics of '''Linux kernel'''
  
 
If not, then go through the''' C/C++''' and '''Linux''' spoken tutorials on this website.
 
If not, then go through the''' C/C++''' and '''Linux''' spoken tutorials on this website.
Line 35: Line 38:
  
 
Ioctl (input/output control)
 
Ioctl (input/output control)
−
|| * It is mainly used to handle some specific operations of a device.
+
||  
 +
* It is mainly used to handle some specific operations of a '''device'''.
  
−
* For example, '''ioctl '''function''' '''can be used to rewind a tape drive.
+
* For example, '''ioctl function''' can be used to rewind a tape drive.
 
* By default, the '''kernel''' does not have a '''system call''' for such '''device operations.'''
 
* By default, the '''kernel''' does not have a '''system call''' for such '''device operations.'''
 
|-  
 
|-  
Line 44: Line 48:
 
'''IOCTl() - Example'''
 
'''IOCTl() - Example'''
  
−
|| In this tutorial, we will learn to transfer data to the driver using the '''ioctl '''function'''.'''
+
|| In this tutorial, we will learn to '''transfer data''' to the '''driver''' using the '''ioctl function.'''
−
The user program''' test.c''' will send and receive integer data to and from the driver.
+
The '''user program test.c''' will send and receive '''integer data''' to and from the '''driver'''.
 
|-  
 
|-  
 
||  
 
||  
Line 51: Line 55:
 
Point to the folder and file in '''desktop'''
 
Point to the folder and file in '''desktop'''
 
Point to the '''files.'''
 
Point to the '''files.'''
−
|| Go to the''' DeviceDriver folder''' in the '''desktop''' which we have created earlier.
+
|| Go to the''' DeviceDriver folder''' in the '''Desktop''' which we have created earlier.
−
I have created a directory named '''Ioctl.'''
+
I have created a '''directory''' named '''Ioctl.'''
 
I have saved '''simple_driver dot c, Makefile '''and''' test dot c files.'''
 
I have saved '''simple_driver dot c, Makefile '''and''' test dot c files.'''
  
Line 60: Line 64:
  
 
'''Code files:'''
 
'''Code files:'''
−
|| The files used in this tutorial are available in the '''Code Files '''link on this tutorial page.
+
||  
 +
*The files used in this tutorial are available in the '''Code Files '''link on this tutorial page.
 
* Please download and extract them
 
* Please download and extract them
 
* Make a copy and then use them while practising
 
* Make a copy and then use them while practising
Line 67: Line 72:
  
 
Type >> '''cd Desktop/DeviceDriver/Ioctl'''
 
Type >> '''cd Desktop/DeviceDriver/Ioctl'''
−
|| Open the terminal by pressing '''ALT+Ctrl+T keys '''simultaneously.
+
|| Open the '''terminal''' by pressing '''ALT+Ctrl+T keys '''simultaneously.
  
−
Go to the directory where '''Ioctl '''is saved on your system.
+
Go to the '''directory''' where '''Ioctl '''is saved on your system.
  
−
Press '''Enter''' key after every command.
+
Press '''Enter''' key after every '''command'''.
 
|-  
 
|-  
 
||  
 
||  
Line 78: Line 83:
 
|| Type '''gedit space simple_driver dot c.'''
 
|| Type '''gedit space simple_driver dot c.'''
  
−
We have already learned the''' open, close, read '''and''' write''' operations on a device'''.'''
+
We have already learnt the''' open, close, read '''and''' write''' operations on a device.
 
|-  
 
|-  
 
| |  
 
| |  
−
| | I have defined the required code to implement the '''ioctl''' functions.
+
| | I have defined the required '''code''' to implement the '''ioctl''' functions.
 
|-  
 
|-  
 
|| HIghlight :
 
|| HIghlight :
Line 92: Line 97:
 
|| We have to include the '''ioctl dot h header file.'''
 
|| We have to include the '''ioctl dot h header file.'''
  
−
The '''macros''' used in the '''ioctl''' '''functions''' are defined in this '''header file.'''
+
The '''macros''' used in the '''ioctl functions''' are defined in this '''header file.'''
−
'''Write''' and '''Read''' commands are defined with the macros as shown here.
+
'''Write''' and '''Read commands''' are defined with the '''macros''' as shown here.
 
|-  
 
|-  
 
|| Highlight
 
|| Highlight
Line 102: Line 107:
 
'''1u'''
 
'''1u'''
 
'''Int'''
 
'''Int'''
−
|| '''IOW''' specifies the '''write''' command operation.
+
|| '''IOW''' specifies the '''write command operation.'''
  
−
'''MAGIC''' is an 8-bit '''magic''' number which is unique to this driver.
+
'''MAGIC''' is an '''8-bit magic''' number which is unique to this '''driver'''.
  
−
'''1u '''specifies the unique command number.
+
'''1u '''specifies the unique '''command''' number.
  
−
It should not be used by any other driver.
+
It should not be used by any other '''driver'''.
  
−
'''Int''' represents the data type of the command argument.
+
'''Int''' represents the '''data type''' of the '''command argument.'''
 
|-  
 
|-  
 
|| Highlight : '''#define MAGIC 'M''''
 
|| Highlight : '''#define MAGIC 'M''''
Line 118: Line 123:
 
https://www.kernel.org/doc/Documentation/ioctl/ioctl-number.txt
 
https://www.kernel.org/doc/Documentation/ioctl/ioctl-number.txt
  
−
|| I have used '''M''' as the '''magic''' number in our driver.
+
|| I have used '''M''' as the '''magic''' number in our '''driver'''.
  
 
For other '''MAGIC''' numbers, refer to this website.
 
For other '''MAGIC''' numbers, refer to this website.
Line 128: Line 133:
 
static int y= 100;
 
static int y= 100;
  
−
|| I have declared two variables '''x''' and '''y'''.
+
|| I have declared two '''variables x''' and '''y'''.
  
−
Data from the user space will be stored in the variable''' x'''.
+
'''Data''' from the '''user space''' will be stored in the '''variable x'''.
  
−
Similarly, data stored in''' y''' variable is passed to the user space.
+
Similarly, '''data''' stored in''' y variable''' is passed to the '''user space'''.
 
|-  
 
|-  
 
|| Highlight
 
|| Highlight
Line 140: Line 145:
 
'''.unlocked_ioctl = mydevice_ioctl'''
 
'''.unlocked_ioctl = mydevice_ioctl'''
  
−
|| We have to write the''' ioctl function protocol''' at the start of the program.
+
|| We have to write the''' ioctl function protocol''' at the start of the '''program'''.
  
−
Add an '''ioctl''' function pointer '''mydevice_ioctl, '''in the '''file operations structure. '''
+
Add an '''ioctl function pointer mydevice_ioctl, '''in the '''file operations structure. '''
 
|-  
 
|-  
 
|| Highlight  
 
|| Highlight  
Line 153: Line 158:
 
|| Let us see the '''ioctl function '''now.  
 
|| Let us see the '''ioctl function '''now.  
  
−
It has three parameters as shown here.
+
It has three '''parameters''' as shown here.
 
'''f '''is the '''file descriptor''' of the appropriate''' device file'''.
 
'''f '''is the '''file descriptor''' of the appropriate''' device file'''.
 
'''ioctl_num''' is the '''ioctl command''' that is called from the''' userspace'''.
 
'''ioctl_num''' is the '''ioctl command''' that is called from the''' userspace'''.
−
'''ioctl_param''' is the argument passed from the '''userspace'''.
+
'''ioctl_param''' is the '''argument passed''' from the '''userspace'''.
 
|-  
 
|-  
 
| |  
 
| |  
−
| | According to the user''' ioctl function''' commands, the '''switch case''' will be executed.
+
| | According to the '''user ioctl function''' commands, the '''switch case''' will be executed.
 
|-  
 
|-  
 
|| HIghlight :
 
|| HIghlight :
 
'''SET_DATA'''
 
'''SET_DATA'''
 
'''copy_from_user()'''
 
'''copy_from_user()'''
−
| | '''copy_from_user '''will copy the user '''ioctl''' parameter to the '''kernel''' space variable''' x.'''
+
| | '''copy_from_user '''will copy the '''user ioctl parameter''' to the '''kernel space variable x.'''
 
|-  
 
|-  
 
|| HIghlight :
 
|| HIghlight :
Line 170: Line 175:
 
'''GET_DATA'''
 
'''GET_DATA'''
 
'''copy_to_user()'''
 
'''copy_to_user()'''
−
|| '''Copy_to_user function '''will copy the value of variable y from the '''kernel''' space to the user space.
+
|| '''Copy_to_user function '''will copy the value of '''variable y''' from the '''kernel space''' to the '''user space'''.
−
Our program is ready with '''ioctl''' function definitions.
+
Our '''program''' is ready with '''ioctl function''' definitions.
 
|-  
 
|-  
 
| | Open the''' terminal.'''
 
| | Open the''' terminal.'''
 
|| Save and close the file.
 
|| Save and close the file.
  
−
Switch back to the terminal.
+
Switch back to the '''terminal'''.
 
|-  
 
|-  
 
||  
 
||  
Line 192: Line 197:
  
 
'''#define GET_DATA _IOR(MAGIC,2u,int)'''
 
'''#define GET_DATA _IOR(MAGIC,2u,int)'''
−
|| This program will pass the arguments and commands to the driver.
+
|| This '''program''' will pass the '''arguments''' and '''commands''' to the '''driver'''.
  
−
We have to define these commands similar to the '''driver commands. '''
+
We have to define these '''commands''' similar to the '''driver commands. '''
  
−
We will use them in the '''ioctl '''function'''.'''
+
We will use them in the '''ioctl function'''.  
 
|-  
 
|-  
 
|| Highlight
 
|| Highlight
Line 203: Line 208:
  
 
'''Static unsigned int h = 0;'''
 
'''Static unsigned int h = 0;'''
−
|| The integer type variables '''g '''and''' h''' are defined as shown here.
+
|| The '''integer type variables g '''and''' h''' are defined as shown here.
  
−
We will use them later on in this code.
+
We will use them later on in this '''code'''.
 
|-  
 
|-  
 
|| Highlight : '''open()'''
 
|| Highlight : '''open()'''
Line 212: Line 217:
  
 
'''File open operation failed.'''
 
'''File open operation failed.'''
−
|| '''open '''function opens the '''new_device'''.
+
|| '''open function''' opens the '''new_device'''.
  
−
If it fails then it will display the failure message and terminate the program.
+
If it fails then it will display the failure message and '''terminate''' the '''program'''.
 
|-  
 
|-  
 
||  
 
||  
Line 232: Line 237:
 
'''SET_DATA'''
 
'''SET_DATA'''
 
'''g'''
 
'''g'''
−
|| The first parameter is the device '''file descriptor number.'''
+
|| The first '''parameter''' is the '''device file descriptor number.'''
  
−
And the second parameter is the command''' '''that needs to be executed.
+
And the second '''parameter''' is the '''command''' that needs to be '''executed'''.
−
 
+
−
The third parameter is the argument to the driver'''.'''
+
  
 +
The third '''parameter''' is the '''argument''' to the '''driver'''.
 
It will display the negative value on failure.
 
It will display the negative value on failure.
 
|-  
 
|-  
Line 247: Line 251:
 
||  
 
||  
  
−
We will pass any integer value at runtime to a '''driver''' using the argument''' g.'''
+
We will pass any '''integer valu'''e at '''runtime''' to a '''driver''' using the '''argument g.'''
−
Similarly, we pass the '''GET_DATA''' command to '''ioctl '''function'''.'''
+
Similarly, we '''pass''' the '''GET_DATA command''' to '''ioctl function'''.
  
−
After execution of this''' '''function, we will get the data from the '''driver''' in '''h '''variable.
+
After execution of this '''function''', we will get the '''data''' from the '''driver''' in '''h variable'''.
 
|-  
 
|-  
 
| | HIghlight '''close()'''
 
| | HIghlight '''close()'''
Line 258: Line 262:
  
 
the '''printf messages.'''
 
the '''printf messages.'''
−
| | The printf messages will display the respective information on the terminal.
+
| | The '''printf''' messages will display the respective information on the '''terminal'''.
 
|-  
 
|-  
 
|| Save the program.
 
|| Save the program.
Line 267: Line 271:
 
|| Save and close the file.
 
|| Save and close the file.
  
−
Switch back to the terminal.  
+
Switch back to the '''terminal'''.  
  
 
Clear the screen.
 
Clear the screen.
Line 276: Line 280:
 
Save a '''file'''.
 
Save a '''file'''.
 
Click on the '''close button.'''
 
Click on the '''close button.'''
−
|| Let us create a '''Makefile''' to compile our '''driver'''.
+
|| Let us create a '''Makefile''' to '''compile''' our '''driver'''.
  
 
Type '''gedit space Makefile.'''
 
Type '''gedit space Makefile.'''
  
−
Copy the code as shown or you can use downloaded '''Makefile'''.
+
Copy the '''code''' as shown or you can use downloaded '''Makefile'''.
  
−
Close the file and switch back to the terminal.
+
Close the file and switch back to the '''terminal'''.
 
|-  
 
|-  
 
|| Type >> '''make all'''
 
|| Type >> '''make all'''
Line 296: Line 300:
  
 
Type >>''' clear'''
 
Type >>''' clear'''
−
| | Type '''sudo space su '''to be a '''superuser''' and type the system '''password'''.
+
| | Type '''sudo space su '''to be a '''superuser''' and type the '''system password'''.
 
|-  
 
|-  
 
|| Type >> '''insmod simple_driver.ko '''
 
|| Type >> '''insmod simple_driver.ko '''
  
−
|| Let’s now load the driver'''.'''
+
|| Let’s now '''load''' the driver'''.'''
  
 
Type '''insmod space simple_driver dot ko '''
 
Type '''insmod space simple_driver dot ko '''
Line 315: Line 319:
 
Type >> '''./test.out'''
 
Type >> '''./test.out'''
  
−
|| Let’s '''compile''' and execute the '''user program.'''
+
|| Let’s '''compile''' and '''execute''' the '''user program.'''
  
 
Type '''gcc space hyphen c space test dot c.'''
 
Type '''gcc space hyphen c space test dot c.'''
Line 329: Line 333:
  
 
The '''printk messages.'''
 
The '''printk messages.'''
−
|| The output message shows that the device is opened successfully.
+
|| The '''output''' message shows that the '''device''' is opened successfully.
  
−
Now, type the integer value that you want to pass to the driver.
+
Now, type the '''integer value''' that you want to '''pass''' to the '''driver'''.
  
−
I’ll type 500.
+
I’ll type '''500'''.
  
−
The output shows the data copied from the '''driver''' to '''user space '''variable''' h'''.
+
The '''output''' shows the '''data''' copied from the '''driver''' to '''user space variable h'''.
−
The print message shows that the device is closed by '''close '''system call.''' '''
+
The '''print''' message shows that the '''device''' is closed by '''close system call.'''
 
|-  
 
|-  
 
| | Type >>''' clear'''
 
| | Type >>''' clear'''
Line 349: Line 353:
 
|| Type the '''dmesg command '''as shown here.
 
|| Type the '''dmesg command '''as shown here.
  
−
The output shows that the''' ioctl function''' of the '''driver''' is executed.
+
The '''output''' shows that the''' ioctl function''' of the '''driver''' is '''executed'''.
  
−
It shows the data from the '''user space '''is copied to the''' kernel space driver variable x.'''
+
It shows the '''data''' from the '''user space '''is copied to the''' kernel space driver variable x.'''
  
 
Clear the screen.
 
Clear the screen.
Line 358: Line 362:
  
 
Type >>''' clear'''
 
Type >>''' clear'''
−
|| Let us unload the '''driver'''.
+
|| Let us '''unload''' the '''driver'''.
  
 
Type '''rmmod simple_driver.ko'''
 
Type '''rmmod simple_driver.ko'''
  
−
Clear the screen. Type exit.
+
Clear the screen. Type '''exit'''.
 
|-  
 
|-  
 
|| Type:
 
|| Type:
Line 371: Line 375:
  
 
'''Highlight'''
 
'''Highlight'''
−
|| In this tutorial, we have discussed IOW and IOR macros.
+
|| In this tutorial, we have discussed '''IOW''' and '''IOR macros'''.
  
−
To know more about other commands, go to the directory '''asm hyphen generic '''as shown:
+
To know more about other '''commands''', go to the directory '''asm hyphen generic '''as shown.
  
 
Let us open the '''ioctl.h''' file.
 
Let us open the '''ioctl.h''' file.
Line 379: Line 383:
 
Type '''cat ioctl.h'''
 
Type '''cat ioctl.h'''
  
−
You can get more details about other commands from the '''ioctl.h file '''
+
You can get more details about other '''commands''' from the '''ioctl.h file '''
 
|-  
 
|-  
 
| |  
 
| |  
Line 387: Line 391:
  
 
Summary:
 
Summary:
−
|| In this tutorial, we learnt* Ioctl function()
+
|| In this tutorial, we learnt
−
* Data transfer between user space and kernel space using '''ioctl''' function
+
* '''Ioctl function()'''
 +
* '''Data transfer''' between '''user space''' and '''kernel space''' using '''ioctl function'''
 
|-  
 
|-  
 
|| Slide 9 :
 
|| Slide 9 :
  
 
Assignment :
 
Assignment :
−
|| As an assignment.# Compile and load '''simple_driver dot c'''
+
|| As an assignment.
−
# Compile and execute '''test.c'''
+
# '''Compile''' and '''load simple_driver dot c'''
−
# Pass a different integer value as per your choice
+
# '''Compile''' and '''execute test.c'''
−
# See the output using '''dmesg command.'''
+
# Pass a different '''integer values''' as per your choice
 +
# See the '''output''' using '''dmesg command.'''
 
|-  
 
|-  
 
|| Slide 10:
 
|| Slide 10:
  
 
About Spoken Tutorial Project:
 
About Spoken Tutorial Project:
−
|| * The video at the following link summarizes the Spoken Tutorial project.
+
||  
 +
* The video at the following link summarizes the Spoken Tutorial project.
 
* Please download and watch it.
 
* Please download and watch it.
 
|-  
 
|-  
Line 407: Line 414:
  
 
Spoken Tutorial workshops :
 
Spoken Tutorial workshops :
−
|| The Spoken Tutorial Project Team:* conducts workshops and
+
|| The Spoken Tutorial Project Team conducts workshops and gives certificates.
−
* gives certificates.
+
  
 
For more details, please write to us.
 
For more details, please write to us.
Line 415: Line 421:
  
 
Forum questions :
 
Forum questions :
−
|| * Please post your timed queries in this forum
+
||Please post your timed queries in this forum
 
|-  
 
|-  
 
|| Slide 13:
 
|| Slide 13:
  
 
Forum for specific questions :
 
Forum for specific questions :
−
|| * Do you have any general or technical questions on Embedded Linux Device Driver?
+
||  
 +
* Do you have any general or technical questions on Embedded Linux Device Driver?
 
* Please visit the FOSSEE forum and post your question.
 
* Please visit the FOSSEE forum and post your question.
 
|-  
 
|-  

Latest revision as of 16:36, 15 December 2020

Visual Cue Narration
Slide 1:

Welcome slide:

Welcome to the spoken tutorial on Input and Output Control
Slide 2:

Learning objectives:

In this tutorial, we will learn about
  • Ioctl function and
  • Data transfer between userspace and kernel space using ioctl function
Slide 3 :

System Requirements:

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
  • Basics of Linux kernel

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

Slide 5:

Ioctl (input/output control)

  • It is mainly used to handle some specific operations of a device.
  • For example, ioctl function can be used to rewind a tape drive.
  • By default, the kernel does not have a system call for such device operations.
Slide 6:

IOCTl() - Example

In this tutorial, we will learn to transfer data to the driver using the ioctl function.

The user program test.c will send and receive integer data to and from the driver.

Point to the folder and file in desktop Point to the files.

Go to the DeviceDriver folder in the Desktop which we have created earlier.

I have created a directory named Ioctl. I have saved simple_driver dot c, Makefile and test dot c files.

I’ll use these files for demonstration.

Slide 7 :

Code files:

  • 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
Open the terminal

Type >> cd Desktop/DeviceDriver/Ioctl

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

Go to the directory where Ioctl is saved on your system.

Press Enter key after every command.

Type >> gedit simple_driver.c

Type gedit space simple_driver dot c.

We have already learnt the open, close, read and write operations on a device.

I have defined the required code to implement the ioctl functions.
HIghlight :

<linux/ioctl.h>

#define MAGIC 'M'#defineSET_DATA_IOW(MAGIC,1u,int)

#defineGET_DATA_IOR(MAGIC,2u,int)

We have to include the ioctl dot h header file.

The macros used in the ioctl functions are defined in this header file. Write and Read commands are defined with the macros as shown here.

Highlight

#define SET_DATA_IOW(MAGIC,1u,int)

MAGIC 1u Int

IOW specifies the write command operation.

MAGIC is an 8-bit magic number which is unique to this driver.

1u specifies the unique command number.

It should not be used by any other driver.

Int represents the data type of the command argument.

Highlight : #define MAGIC 'M'

M

https://www.kernel.org/doc/Documentation/ioctl/ioctl-number.txt

I have used M as the magic number in our driver.

For other MAGIC numbers, refer to this website.

Highlight:

static int x = 0;

static int y= 100;

I have declared two variables x and y.

Data from the user space will be stored in the variable x.

Similarly, data stored in y variable is passed to the user space.

Highlight

static long mydevice_ioctl(struct file *f,unsigned int ioctl_num,unsigned long ioctl_param);

.unlocked_ioctl = mydevice_ioctl

We have to write the ioctl function protocol at the start of the program.

Add an ioctl function pointer mydevice_ioctl, in the file operations structure.

Highlight

static long mydevice_ioctl(struct file *f,unsigned int ioctl_num,unsigned long ioctl_param)

f Ioctl_num ioctl_param

Let us see the ioctl function now.

It has three parameters as shown here. f is the file descriptor of the appropriate device file. ioctl_num is the ioctl command that is called from the userspace. ioctl_param is the argument passed from the userspace.

According to the user ioctl function commands, the switch case will be executed.
HIghlight :

SET_DATA copy_from_user()

copy_from_user will copy the user ioctl parameter to the kernel space variable x.
HIghlight :

GET_DATA copy_to_user()

Copy_to_user function will copy the value of variable y from the kernel space to the user space.

Our program is ready with ioctl function definitions.

Open the terminal. Save and close the file.

Switch back to the terminal.

Type >> gedit test.c

Let’s open the user program.

Type gedit space test dot c.

Highlight

#define MAGIC 'M'

#define SET_DATA _IOW(MAGIC,1u,int)

#define GET_DATA _IOR(MAGIC,2u,int)

This program will pass the arguments and commands to the driver.

We have to define these commands similar to the driver commands.

We will use them in the ioctl function.

Highlight

Static unsigned int g = 0;

Static unsigned int h = 0;

The integer type variables g and h are defined as shown here.

We will use them later on in this code.

Highlight : open()

if(fd < 0)

File open operation failed.

open function opens the new_device.

If it fails then it will display the failure message and terminate the program.

Highlight

ioctl(fd, SET_DATA,&g)<0)

ioctl() function.

The user ioctl function will internally call the driver’s ioctl function.

You can use the ioctl system call only after opening the device file.

HIghlight:

fd SET_DATA g

The first parameter is the device file descriptor number.

And the second parameter is the command that needs to be executed.

The third parameter is the argument to the driver. It will display the negative value on failure.

Highlight

scanf() GET_DATA, h ioctl()

We will pass any integer value at runtime to a driver using the argument g. Similarly, we pass the GET_DATA command to ioctl function.

After execution of this function, we will get the data from the driver in h variable.

HIghlight close() The close system call will close the new_device file.
Highlight

the printf messages.

The printf messages will display the respective information on the terminal.
Save the program.

Open the terminal

Type >> clear

Save and close the file.

Switch back to the terminal.

Clear the screen.

Type >> gedit Makefile Save a file. Click on the close button.

Let us create a Makefile to compile our driver.

Type gedit space Makefile.

Copy the code as shown or you can use downloaded Makefile.

Close the file and switch back to the terminal.

Type >> make all Now, let us compile the driver.

Type make space all.

Type >> clear Clear the screen.
Type >> sudo su

Type >> clear

Type sudo space su to be a superuser and type the system password.
Type >> insmod simple_driver.ko Let’s now load the driver.

Type insmod space simple_driver dot ko

Type >> clear Clear the screen.

Type >> gcc -c test.c

Type >> gcc -o test.out test.o

Type >> ./test.out

Let’s compile and execute the user program.

Type gcc space hyphen c space test dot c.

Type gcc space hyphen o space test dot out space test dot o.

Type dot slash test dot out.

Highlight

the respective printk message

Type the integer value

The printk messages.

The output message shows that the device is opened successfully.

Now, type the integer value that you want to pass to the driver.

I’ll type 500.

The output shows the data copied from the driver to user space variable h. The print message shows that the device is closed by close system call.

Type >> clear Clear the screen.
Highlight

Type >> dmesg | grep simple_driver Highlight : Respective printk messages. Type >> clear

Type the dmesg command as shown here.

The output shows that the ioctl function of the driver is executed.

It shows the data from the user space is copied to the kernel space driver variable x.

Clear the screen.

Type rmmod simple_driver.ko

Type >> clear

Let us unload the driver.

Type rmmod simple_driver.ko

Clear the screen. Type exit.

Type:

cd /usr/include/asm-generic/

Cat ioctl.h

Highlight

In this tutorial, we have discussed IOW and IOR macros.

To know more about other commands, go to the directory asm hyphen generic as shown.

Let us open the ioctl.h file.

Type cat ioctl.h

You can get more details about other commands from the ioctl.h file

With this we come to the end of this tutorial. Let us summarize.
Slide 8 :

Summary:

In this tutorial, we learnt
  • Ioctl function()
  • Data transfer between user space and kernel space using ioctl function
Slide 9 :

Assignment :

As an assignment.
  1. Compile and load simple_driver dot c
  2. Compile and execute test.c
  3. Pass a different integer values as per your choice
  4. See the output using dmesg command.
Slide 10:

About Spoken Tutorial Project:

  • The video at the following link summarizes the Spoken Tutorial project.
  • Please download and watch it.
Slide 11:

Spoken Tutorial workshops :

The Spoken Tutorial Project Team conducts workshops and gives certificates.

For more details, please write to us.

Slide 12:

Forum questions :

Please post your timed queries in this forum
Slide 13:

Forum for specific questions :

  • Do you have any general or technical questions on Embedded Linux Device Driver?
  • Please visit the FOSSEE forum and post your question.
Slide 14:

Acknowledgment:

The Spoken Tutorial Project is funded by MHRD, Government of India.
Slide 15:

Thank you slide:

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

This is usha signing off.

Thanks for watching.

Contributors and Content Editors

Nancyvarkey, Nirmala Venkat

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