OS Lab — Exercise 2: lunix:TNG (NTUA 2023–24)

This README covers Exercise 2, which involved writing a character device (chrdev) driver for the Linux kernel. The full report is in ex2-lunix/ex2-lunix-report.pdf.

Goal

Implement and document the character-device side of lunix:TNG so that sensor readings are exposed correctly to user space.

Key changes (in lunix-chrdev.c)

• lunix_chrdev_state_needs_refresh() — Check the state timestamp against the sensor’s last update to decide if a refresh is needed.
• lunix_chrdev_state_update() —
  • Uses: sensor, new_data, raw data, looked_up_data, ret, digit, i.
  • Inside the spinlock: verify refresh need, pull raw data from the sensor struct, update timestamp and new_data.
  • Outside the lock: convert raw data via lookup tables, format, and write into the state buffer.
• lunix_chrdev_open() — Get minor with iminor, derive sensor type (e.g., minor/8), kzalloc a per-file state, store in file->private_data, set type/number, init the semaphore.
• lunix_chrdev_read() — down_interruptible on the state semaphore; if at *f_pos == 0 wait for fresh data (signal-aware); compute bytes to return, copy_to_user, release the semaphore, return count.
• lunix_chrdev_release() — Free the per-file state with kfree.
• lunix_chrdev_init() — Register device numbers with register_chrdev_region and add the device with cdev_add.