Create a character device in the Linux 2.6 kernel, automatically obtain the device number, and create a simple example of a device Node

 

I forgot a very simple C code from where I found it a long time ago, completed the character device registration, automatically obtained the device number (Master/Slave), and automatically created the device node.

I have posted some similar questions for your reference.

Thanks to the original author of the Code: zengxiaolong

The following code is compiled in the 6.35-22 kernel.

Create_chrdev.c:

// Create_chrdev.c
//---------------------------------------------
# Include <Linux/types. h> // dev_t
# Include <Linux/cdev. h> // struct cdev
# Include <Linux/fs. h> // alloc_chrdev_region ()
# Include <Linux/device. h> // class_create ()

Dev_t devid;
Static struct cdev * led_cdev;
Static int led_major = 0;
Static int led_minor = 0;
Static struct class * led_class;

Static struct file_operations led_fops = {
. Owner = this_module,
};

Static int _ init hello_init (void)
{
Int err;

// Initialize cdev
Led_cdev = cdev_alloc ();
Cdev_init (led_cdev, & led_fops );
Led_cdev-> owner = this_module;

// Obtain the master device number dynamically (dev_t devid contains the "master device number" and "sub-device number" Information)
Alloc_chrdev_region (& devid, 66, 1, "led"); // assign one device number from 66
Led_major = major (devid );
Led_minor = minor (devid );
Printk (kern_info "I was assigned major Number % d. \ n", led_major );
Printk (kern_info "I was assigned minor Number % d. \ n", led_minor );

// Register character devices (1)
Err = cdev_add (led_cdev, devid, 1 );
If (ERR ){
Printk (kern_notice "error % d adding device \ n", err );
Return-1;
}

Led_class = class_create (this_module, "led_class1"); // a directory named led_class1 is created under the/sys directory.
If (is_err (led_class )){
Printk (kern_info "create class error \ n ");
Return-1;
}
Device_create (led_class, null, devid, null, "led" "% d", minor (devid ));

// Class_device_create should be used in earlier versions 2.6, before 2.6.27? 2.6.29? Forgot. In this step, an led66 device file is created under the/dev directory.

Return 0;
}

Static void _ exit hello_exit (void)
{
Unregister_chrdev_region (devid, 1 );
Cdev_del (led_cdev );

Device_destroy (led_class, devid); // class_device_destroy should be used in earlier versions than 2.6.27? 2.6.29? Forgot.
Class_destroy (led_class );
}

Module_init (hello_init );
Module_exit (hello_exit );

Module_license ("GPL ");
Module_author ("zengxiaolong ");
Module_description ("A sample driver ");
Module_supported_device ("testdevice ");

 

Makefile (for PC ):

OBJ-M: = create_chrdev.o
Kerneldir: =/lib/modules/$ (shell uname-R)/build
Default:
Make-C $ (kerneldir) M = $ (shell PWD) Modules
Install:
Insmod create_chrdev.ko
Uninstall:
Rmmod create_chrdev
Clean:
Make-C $ (kerneldir) M = $ (shell PWD) clean

Makefile (for ARM ):

OBJ-M: = create_chrdev.o
Kerneldir: =/usr/local/src/arm2440/kernel-2.6.29 # It is your arm Kernel folder
Default:
Make-C $ (kerneldir) M = $ (shell PWD) Modules
Install:
Insmod create_chrdev.ko
Uninstall:
Rmmod create_chrdev
Clean:
Make-C $ (kerneldir) M = $ (shell PWD) clean