RANDOM NUMBERS GENERATING KERNEL MODULE

I - Descriptions:

1. Feature: This module generate random numbers in a range of (-limit, limit).
2. Files and Folders:
   • randnum_mod.c: main source
   • Makefile and Kbuild: this module is built using Kbuild method
   • README.md
   • ~/user_app: contains randnum.c and its Makefile (for the user to get random numbers)
   • ~/test (not recommended): contains randnum_mod.ko and randnum.exe that are already built

   Built and tested successfully on:

   • ubuntu 16.04 LTS 64-bit
   • kernel version: 4.15.0-70-generic

3. Funtions in randnum_mod.c:
   • number_len(int num) : get number of digits
   • mypow(int base, int exp) : simple power function
   • number_to_str(int num, char* str) : convert from int to char* - equivalent to string::itoa()
   • str_to_number(int *num, char str)* : convert from char* to int - equivalent to string::atoi()
   • randnum_open(struct inode *i, struct file *f) : will be assigned to syscall "open"
   • randnum_close(struct inode *i, struct file *f) : will be assigned to syscall "release"
   • randnum_read(struct file *f, char __user *buf, size_t len, loff_t *off) : will be assigned to syscall "read"
   • randnum_write(struct file *f, const char __user *buf, size_t len, loff_t *off) : will be assigned to syscall "write" (in this program, its specific task is to change the range of generation)
   • __init randnum_init(void) : initialize the module
   • __exit randnum_exit(void) : exit the module

II - Makefiles:

1. randnum_mod.c

• $ ~/Randnum$ make
• The result should look like:

   make -C /lib/modules/``uname -r``/build M=``pwd`` modules
   make[1]: Entering directory '/usr/src/linux-headers-4.15.0-70-generic'
   CC [M]  /home/osboxes/Modules/randnum_mod.o
   Building modules, stage 2.
   MODPOST 1 modules
     CC      /home/osboxes/Modules/randnum_mod.mod.o
     LD [M]  /home/osboxes/Modules/randnum_mod.ko
   make[1]: Leaving directory '/usr/src/linux-headers-4.15.0-70-generic'
  

2. randnum.c

• $ ~/Randnum/user_app$ make
• The result should look like:

  cc -o randnum randnum.c

III - Module manipulations:

1. insert:
   • $ ~/Randnum$ sudo insmod randnum_mod.ko
2. remove:
   • $ ~/Randnum$ sudo rmmod randnum_mod.ko
3. get permission to access device file:
   • $ ~/Randnum$ sudo chmod 666 dev/randnum_dev

IV - Use the app:

1. Run:

• $ ~/Randnum/user_app$ ./randnum
• The result should look like:

   Select options:
   	o (to open a device node)
   	c (to close the device node)
   	r (to read data from device node)
   	s (to set a new random range, max = 1000000)
   	q (to quit the application)
   Enter your option:
  

2. Commands:

• o : open the device file
• c : close the device file
• r : read data from device file
• s : set a new random range, max = 1000000
• q : quit the application

V - References:

1. Core knowledges and user interface:

   https://vimentor.com/vi/course/linux-device-driver?type=lesson

2. randnum_mod.c is based on:

   https://sites.google.com/site/embedded247/ddcourse/device-drivers-phan-5-character-device-files

Nguyen Minh Vu - Nov, 2019