How to create a device in /dev automatically upon loading of the kernel module for a device driver?

Question

I am attempting to develop Linux device drivers and as my first attempt I am trying to develop a char device driver that has the following file options,

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Answer 1

• Include the header file linux/device.h and linux/kdev_t.h

• static struct class c_dev;

• static struct dev_t dev;

Add the below API 's inside __init fuction of the driver

• cl = class_create(THIS_MODULE ,"x");

where x - Name to be displayed inside /sys/class/ when driver is loaded.

• Use device_create () kernel api with device_create(cl, NULL, dev, NULL, "d");

where d - device file to be created under /dev.

where dev is variable for the first device number that is initialized during the usage of alloc_chrdev_region API for dynamic allocation of major number for the driver

For Further reference please go through the link http://opensourceforu.com/2011/04/character-device-files-creation-operations/

Answer 2

I could see entries within /dev after creating node by running following command at console.

sudo mknod -m 0666 /dev/msio c 22 0

The user was not root, so I had to use sudo. My entry name was msio, a character device with major and minor number 22, 0 respectively.

I will let you know if this can be achieved programatically.

Answer 3

There are two ways to create the device file in /dev

• Manually creation of a device file using mknod
$ mknod -m <permission> <name> <device_type> <major> <minor>
  here
  name is the name of device driver,
  device_type is the type of the device (b-> block devices , c-> char devices),
  major & minor are the device numbers,
  permission is optional you can change it after creation, by using chmod.
  
• Dynamic creation using .
  

dev_t dev=0;
static struct class *devicefileClass;
deviceFileClass=class_create(THIS_MODULE,"device_name");
device_create( deviceFileClass , NULL , dev ,"device_name")

NOTE class_create , device_create function call should be in your __init function. and inlude <linux/device.h>,<linux/kdev_t>.

Answer 4

CONFIG_DEVTMPFS is quite nice if you can use that with your distro. You can have the kernel automount that for you at boot (CONFIG_DEVTMPFS_MOUNT) or mount it manually (mount -t devtmpfs none /dev).

Answer 5

First you have to use : sudo mknod /dev/devicename c 81 0

It creates device file in /dev but you have to give it read/write permission. to do so,

sudo chmod 777 /dev/devicename

Done !!!

Answer 6

You may have to create some udev rules to tell the system what device node(s) you need it to create.