File Operations on Character Devices (Screenplay)

Hooks Necessary

# cat /dev/my_driver-0
cat: /dev/my_driver-0: Invalid argument
# strace cat /dev/my_driver-0
openat(AT_FDCWD, "/dev/my_driver-0", O_RDONLY) = 3
read(3, 0x7f3d11330000, 131072)         = -1 EINVAL (Invalid argument)

Implement open(), read(), write()

  • Only debug output; no access to device (or any state held by it)

  • read() and write() initially just like /dev/null


  • request parameter: like protocol identifier

  • ignore data for now

Userspace test program

  • Use request = 666 as ioctl request ⟶ Inappropriate ioctl for device (ENOTTY)