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Exercise 1: Pseudo Character Driver (Single Device) - Requirements

Requirements

• Write a character driver to deal with a pseudo character device

• The pseudo-device is a memory buffer of some size

• The driver you write must support reading, writing and seeking to this driver

• Test the driver functionality by running user-level command such as echo, dd, cat and by writing user level programs

Connection Establishment between Device File Access and the Driver

1. Create device number

   • Request the kernel to dynamically allocate the device numbers(s)

2. Make a char device registration with the Virtual File System (VFS). (CDEV_ADD)

3. Create device files

4. Implement the driver's file operation methods for open, close, read, write, llseek, etc.

Expected Outcome

• Do make host and see if you are getting pcd.ko from pcd.c.

• Insert the LKM (sudo insmod pcd.ko), run dmesg and see if the messages are getting printed.

• Check /sys/class/ if you see pcd_class/ which should be created by the class_create() kernel function.

  • pcd_class/ directory should contain pcd (the same name as your LKM) directory

  • pcd_class/pcd/ directory should contain dev file whose contents is the device number <major:minor>

  • pcd_class/pcd/ directory should also contain uevent whose contents is major number, minor number and devname.

  udev creates the device file under /dev directory according to these details which are created and populated by the device_create() kernel function.

• Check /dev/ if you see the device file pcd.

• Remove the LKM (sudo rmmod pcd.ko), run dmesg and see if the messages are getting printed.