A simple example of a Linux kernel module

1. The overall structure of the Linux kernel is very large and contains many components, using these components in two ways:

① directly into the kernel file, either Zimage or bzimage (problem: excessive memory consumption)

② Dynamic Additions

* The module itself is not compiled into the kernel file

* Dynamically install or uninstall during kernel runtime, as required

2. Dynamic installation and uninstallation of kernel modules

① installation Insmod

Example: Insmod/home/dnw_usb.ko

② Uninstalling Rmmod

Example: Rmmod dnw_usb

③ View Lsmod

Example: Lsmod

3. Module declaration

①module_license ()

②module_author ()

③module_description ()

④module_version ()

4. Module parameters

The ① module parameter is used to pass parameters to the module when the module is loaded

② specifying variables to save module parameters via macro Module_param

Module_param (name, type, perm)

* Name: Names of variables

* Type: Variable type. BOOL: boolean, int: integer, Charp: String

* Perm is access rights. S_irugo: Read permission, s_iwusr: Write permission

③ Simple Example

int 3  int, sirugo);

Command line: insmod Xxx.ko a = 10

5. Symbol Export

① if a function or global variable in a kernel module wants to be used by another module, it must be exported

② kernel symbol export using macros

Export_symbol (symbol name)

EXPORT_SYMBOL_GPL (symbol name)

Note: Where EXPORT_SYMBOL_GPL can only be used for modules that contain GPL licenses

6. Kernel Module Simple Example

① Module Code:

#include <linux/init.h><linux/module.h>staticint  hello_init () {    PRINTK (kern_warning"Hello World initlizing\n");     return 0 ;    } Static void Hello_exit () {    printk (kern_warning"Hello World exiting\n");    } Module_init (Hello_init); Module_exit (hello_exit);

②makefile:

Obj-m: = helloworld.okdir:=/home/linux/kernal/linux-2.6.  in All :     -C $ (Kdir) m=$ (PWD) modules cross_compile=arm-linux-arch=arm clean    :    -F *.o *.ko *.order *. symvers    

A simple example of a Linux kernel module