DeveloperGuide

@@ This LKM Developer Guide created for simple kernel modules. @@

Testing on ubuntu 18.04

@Install package:

    # os's spesific kernel source and developer kit  
    $ sudo apt-get install build-essential linux-headers-$(uname -r)
 
@Makefile parameters for used compile lkm

    make -C /lib/modules/$(shell uname -r)/build/ M=$(PWD) modules

@Programming main requires

     ## Headers 
	#include <linux/module.h> /* included all modules */
	#include <linux/kernel.h> /* KERN_INFO */
	#include <linux/init.h>	 /* for macro */
	#include <linux/fs.h>     /* for filp */
	#include <asm/uaccess.h>  /* for segment descriptors */
	#include <linux/kthread.h> /* for thread */	
	#include <linux/delay.h> /* for delay msec */


     ## Macros
         MODULE_LICENSE("GPL") -> LKM's type of licanse
         MODULE_AUTHOR("Atakan Akbulut") -> author
	 MODULE_DESCRIPTION("Hello from LKM") -> you can explain lkm's descr.
	 MODULE_VERSION("0.1"); -> version info

     ## Install, remove, get lkm'm info 
        sudo insmod module.ko -> run lkm to kernel
        sudo rmmod module.ko -> remove from kernel
        sudo modinfo module.ko -> get info


@Debugging
      ## Kernel use printk instead of printf
	 KERN_EMERG -> mostly emergency crash
         KERN_ALERT -> immediate action
         KERN_CRIT
         KERN_ERR -> for examle cannot find FUZE
         KERN_WARNING
         KERN_NOTICE
	 KERN_INFO
	 KERN_DEBUG
      ## logs inside dmesg or /var/log/kern.log

@@@@@ KERNEL_DS is instead of set_fs(get_fs()) probability higher than 5 kernel version

@@@@@ read / write  functions vfs_read and vfs_write good..

@@@@@ filp_open -> file open like fopen offset perhaps 0 ..

@@@@@ filp_open modes -> O_RDONLY, O_CREAT, O_RDWR, ...

@@@@@ threading -> struct task_struct *ts1; (create task and start kthread) 
		kthread_run(kthread_func, NULL, "thread-pool-name")

@@@@@ current -> current->comm, current->pid return pool name and pid