SYS-205 Assessment 1 - Building a driver for heartydev

The goal of this assessment is to evaluate whether you briefly understand how applications and operating systems interact with devices. You will implement a simple character device driver to demonstrate this knowledge.

Setting up

Step 1 - Build a driver module

In this task, you will need to simply build a driver using the Makefile. Even though you can type the following commands, I would recommend you look at the commands in the Makefile to see how the compilation process works.

make

If you are not sure what is the kernel module, you can read more at https://sysprog21.github.io/lkmpg/.

Step 2 - Load a driver

Since your driver is a C module, you can use insmod to load it as follows.

sudo insmod heartydev.ko

To verify, you can use the following commands.

cat /proc/modules | grep heartydev
cat /proc/devices | grep heartydev

Also, the heartydev_init function will be executed. The output will be printed out in the /var/log/syslog file. You can use the following commands to see.

tail /var/log/syslog

If you want to remove the module, you can use the following command.

sudo rmmod heartydev

Code Quality (20 points)

You should follow a good coding convention. In this class, please stick with the CMU 15-213's Code Style.

https://www.cs.cmu.edu/afs/cs/academic/class/15213-f24/www/codeStyle.html

Task 1 - Implement heartydev's write and read (20 points)

Since we do not have a real device, interacting with the device will be to read/write to the driver buffer instead.

Task 1.1 - Implement heartydev_write (10 points)

Your task is to implement the heartydev_write by copying the text from the user buffer (buf) into the driver buffer. Note that you may need to create the driver buffer by yourself.

To verify, you should be able to call heartydev_write through the following command.

echo 'hello, heartydev!' > /dev/heartydev

Task 1.2 - Implement heartydev_read (10 points)

Your task is to implement the heartydev_read by copying the text from the driver buffer into the user buffer. However, all the lowercase English letters must be capitalized.

To verify, you should be able to call heartydev_read through the following command.

cat /dev/heartydev

Task 2 - Implement heartydev's ioctl (30 points)

You need to implement four ioctl commands and show that user applications can call this driver command. The commands are listed as follows:

Task 2.1 - Implement the HEARTYDEV_READ_CNT command (10 points)

HEARTYDEV_READ_CNT must show the current number of heartydev_read function calls.

Task 2.2 - Implement the HEARTYDEV_WRITE_CNT command (10 points)

HEARTYDEV_WRITE_CNT must show the current number of heartydev_write function calls.

Task 2.3 - Implement the HEARTYDEV_BUF_LEN command (10 points)

HEARTYDEV_BUF_LEN must show the current length of the driver buffer. If there is nothing in the buffer, it should show 0.

Task 3 - Implement device modes (30 points)

You will need to implement two more device modes using the prior knowledge you learned.

Task 3.1 - ioctl for changing the device's mode (10 points)

Your task is to implement the ioctl command that changes the device's mode. There will be in total of three modes. The driver we previously implemented should be in the mode called UPPER.

Task 3.2 - Implement the NORMAL mode (10 points)

Your task is to implement the NORMAL mode, where the driver should not capitalize the text while doing heartydev_read.

Task 3.3 - Implement the LOWER mode (10 points)

Your task is to implement the LOWER mode, where the driver should, instead of doing capitalization, change all capitalized English letters into lowercase letters while doing heartydev_read.

Grading

• 20% - Task 1
• 30% - Task 2 (If task 1 is not complete, task 2 will not be graded.)
• 30% - Task 3 (If tasks 1 and 2 are not complete, task 3 will not be graded.)
• 20% - Code Style (If tasks 1, 2, and 3 are not complete, the code style will not be graded.)

References

• https://olegkutkov.me/2018/03/14/simple-linux-character-device-driver/
• https://github.com/backendeveloper/Linux-Character-Device
• https://embetronicx.com/tutorials/linux/device-drivers/ioctl-tutorial-in-linux/