取得 wifi parameters for linux kernel

想抓取wifi的資訊可利用linux kernel的struct netdev
所提供的struct iw_handler_def wireless_handlers來拿取
這是透過wireless_handlers內有個standard的指標函數,
可提供wireless device driver實作,
因此我們可透過standard指標函數來拿取wireless相關資訊

struct net_device
{
...
const struct iw_handler_def * wireless_handlers;
...
}


struct iw_handler_def
{
...
/* Array of handlers for standard ioctls
* We will call dev->wireless_handlers->standard[ioctl - SIOCSIWCOMMIT]
*/
const iw_handler * standard;
...
}


typedef int (*iw_handler)(struct net_device *dev, struct iw_request_info *info, union iwreq_data *wrqu, char *extra);


以zd1211rw driver為例：

#define WX(x) [(x)-SIOCIWFIRST]

static const iw_handler zd_standard_iw_handlers[] = {
WX(SIOCGIWNAME) = iw_get_name,
WX(SIOCGIWNICKN) = iw_get_nick,
WX(SIOCSIWFREQ) = iw_set_freq,
WX(SIOCGIWFREQ) = iw_get_freq,
...
};


可以看到這些Wireless Identification的定義：

/* Wireless Identification */
#define SIOCSIWCOMMIT 0x8B00
#define SIOCGIWNAME 0x8B01

#define SIOCSIWNWID 0x8B02 /* set network id (pre-802.11) */
#define SIOCGIWNWID 0x8B03 /* get network id (the cell) */
#define SIOCSIWFREQ 0x8B04 /* set channel/frequency (Hz) */
#define SIOCGIWFREQ 0x8B05 /* get channel/frequency (Hz) */
...
wireless.h:335:#define SIOCIWFIRSTPRIV 0x8BE0
wireless.h:351:#define SIOCIWFIRST 0x8B00


倘若我們想抓取frequency(channel) of current link ，

可直接call function
net_dev -> wireless_handlers ->
standard[SIOCGIWFREQ - SIOCSIWCOMMIT](net_dev, NULL, (void *) & my_freq, NULL);


然後透過my_freq.m就能抓取現在的freq

struct iw_freq my_freq;

struct iw_freq
{
__s32 m; /* Mantissa */
__s16 e; /* Exponent */
__u8 i; /* List index (when in range struct) */
__u8 flags; /* Flags (fixed/auto) */
};


進而推出wifi的rssi

COSCUP 2010

今天的[COSCUP]在中研院舉辦,
去了第四年XD,還是一樣熱血,
而且今年參加人數大爆炸XD

今年的議程主要以Open Web and Mobile Technologies為主

以下為一些議程的心得:

Frontend Development Enviornment, josephj

這個議程滿有趣的,
透過將HTML/CSS/JavaScript 的模組化與自動化
可很嚴謹的制定模組policy
這個design pattern或許也可用於其他地方

Debugging: Linux Kernel by Ftrace, AceLan

Ftrace的工具, 可透過/proc的檔案系統來進行trace kernel function
但很可惜, 目前只僅次於function, 誰call誰, 誰被call

Be 「Android」, Tick Chen + Matt Hsu

很cool的機器人, 透過馬達 <-I2C-> ARM <-buletooth-> Android
來控制機器人, 可惜沒看到開全速的樣子XD

打造特製的 Android Toolchain, jserv

透過"搞系統程式絕對不是「不入流」"開場, 超high
jserv前輩很強~~
一路trace GNU Toolchain發展開發並發現android toolchain的git中無說明
無法自制android toolchain，因此開始打造從無到有的android toolchain,
超cool

Add new system call

kernel版本:2.6.33-rc2

新增自行定義的system call步驟如下:

1. edit arch/x86/kernel/syscall_table_32.S, add

.long sys_mysystemcall /* 338 */

2. edit include/asm-i386/unistd.h, add

#define __NR_mysystemcall 338

3. create new file, arch/x86/kernel/systemcall.c
(defined filename yourself)

#include <linux/linkage.h>
#include <linux/kernel.h>

asmlinkage int sys_mysystemcall(void)
{
printk("mysystemcall\n");
return 0;
}

4. edit arch/x86/kernel/Makefile, add

obj-y += systemcall.o


5. compiler kernel

root@shulong-desktop:/home/shulong/linux-2.6.33-rc2# make clean && make


6. writing code for user mode, create new file test.c

#include <linux/unistd.h>
#include <sys/syscall.h>
#include <sys/types.h>

#define __NR_mysystemcall 338
#define mysystemcall() syscall(__NR_mysystemcall);

int main ()
{
mysystemcall();
return 0;
}

7. compiler test.c

root@shulong-desktop:~# gcc -Wall test.c -o systemcall

8. execute systemcall

root@shulong-desktop:~# ./systemcall
[ 39.289669] mysystemcall


就可順利加入自行定義的system call。