Linux Kernel Module Parameters

Reference :
1.  http://tldp.org/LDP/lkmpg/2.6/html/x323.html
2.  http://makelinux.com/ldd3/chp-2-sect-8

前言：
        這個文章是我最近在寫Linux Kernel Device Driver遇到的問題，所以想說寫下來才不會忘記，也順便分享出來讓有需要的人更快可以上手，如果對於我寫的文章有問題或是有更好的想法，也請大家一起交流。

相關參數介紹：

        在寫Linux Kernel Module的時候，我們用insmod或 modprobe安裝的時候，可以對module填入我們想要的參數，例如：
               
            $> sudo  insmod mymod.ko number=10


       這樣的好處讓你的Kernel modules在設計的時候會比較有彈性，然後這些參數在Kernel module是經過module_param這個Macro來處理。以下是對module_param的介紹：


module_param( param name, data type, permissions bits);


 1. param name : 參數名稱
 2. data type       : 資料型態

• bool
• invbool
• A boolean (true or false) value (the associated variable should be of type int). The invbool type inverts the value, so that true values become false and vice versa.
• charp
• A char pointer value. Memory is allocated for user-provided strings, and the pointer is set accordingly.
• int
• long
• short
• uint
• ulong
• ushort

3. permissions bits : The final module_param field is a permission value; you should use the definitions found in . This value controls who can access the representation of the module parameter in sysfs. If perm is set to 0, there is no sysfs entry at all
(有關參數的權限，但我還不太懂之後比較瞭解再補充。)


        再另外補充一下macro就是MODULE_PARM_DESC，這個marco主要就是讓你可以用modinfo這個工具去讀取kernel module的資訊時顯示這個module參數的資訊。以下是例子：


static short int myshort = 1;

module_param(myshort, short, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
MODULE_PARM_DESC(myshort, "A short integer");


完整的範例：


# Makefile




  obj-m += hello-5.o
  
   all:
           make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
   
   clean:
           make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
                                                                       

# hello-5.c (這是由Reference 1的網頁中直接拿來做範例)

/* * hello-5.c - Demonstrates command line argument passing to a module. */ #include #include #include #include #include MODULE_LICENSE("GPL"); MODULE_AUTHOR("Peter Jay Salzman"); static short int myshort = 1; static int myint = 420; static long int mylong = 9999; static char *mystring = "blah"; static int myintArray[2] = { -1, -1 }; static int arr_argc = 0; /* * module_param(foo, int, 0000) * The first param is the parameters name * The second param is it's data type * The final argument is the permissions bits, * for exposing parameters in sysfs (if non-zero) at a later stage. */ module_param(myshort, short, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP); MODULE_PARM_DESC(myshort, "A short integer"); module_param(myint, int, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH); MODULE_PARM_DESC(myint, "An integer"); module_param(mylong, long, S_IRUSR); MODULE_PARM_DESC(mylong, "A long integer"); module_param(mystring, charp, 0000); MODULE_PARM_DESC(mystring, "A character string"); /* * module_param_array(name, type, num, perm); * The first param is the parameter's (in this case the array's) name * The second param is the data type of the elements of the array * The third argument is a pointer to the variable that will store the number * of elements of the array initialized by the user at module loading time * The fourth argument is the permission bits */ module_param_array(myintArray, int, &arr_argc, 0000); MODULE_PARM_DESC(myintArray, "An array of integers"); static int __init hello_5_init(void) { int i; printk(KERN_INFO "Hello, world 5\n=============\n"); printk(KERN_INFO "myshort is a short integer: %hd\n", myshort); printk(KERN_INFO "myint is an integer: %d\n", myint); printk(KERN_INFO "mylong is a long integer: %ld\n", mylong); printk(KERN_INFO "mystring is a string: %s\n", mystring); for (i = 0; i < (sizeof myintArray / sizeof (int)); i++) { printk(KERN_INFO "myintArray[%d] = %d\n", i, myintArray[i]); } printk(KERN_INFO "got %d arguments for myintArray.\n", arr_argc); return 0; } static void __exit hello_5_exit(void) { printk(KERN_INFO "Goodbye, world 5\n"); } module_init(hello_5_init); module_exit(hello_5_exit);

     $> make
     $> sudo insmod hello_5.ko

用dmesg去看一下，Kernel Module秀出什麼資訊 。
     $> dmesg


[ 6532.204976] Hello, world 5
[ 6532.204979] =============
[ 6532.204983] myshort is a short integer: 1
[ 6532.204986] myint is an integer: 420
[ 6532.204989] mylong is a long integer: 9999
[ 6532.204991] mystring is a string: blah
[ 6532.204994] myintArray[0] = -1
[ 6532.204996] myintArray[1] = -1
[ 6532.204999] got 0 arguments for myintArray.

   $> sudo rmmod hello_5.ko

   $>  sudo insmod hello_5.ko  mystring="abcde" myintArray=1,12

[ 6915.780582] Hello, world 5

[ 6915.780585] =============

[ 6915.780592] myshort is a short integer: 1

[ 6915.780597] myint is an integer: 420

[ 6915.780601] mylong is a long integer: 9999

[ 6915.780605] mystring is a string: abcde

[ 6915.780609] myintArray[0] = 1

[ 6915.780613] myintArray[1] = 12

[ 6915.780617] got 1 arguments for myintArray.

如果你想要看Kernel module的相關訊息的話，請使用:

     $> modinfo hello_5.ko


filename:       hello_5.ko
author:         Peter Jay Salzman
license:        GPL
srcversion:     A704327C32F7F311666C13C
depends:    
vermagic:       3.0.0-12-generic SMP mod_unload modversions
parm:           myshort:A short integer (short)
parm:           myint:An integer (int)
parm:           mylong:A long integer (long)
parm:           mystring:A character string (charp)
parm:           myintArray:An array of integers (array of int)