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linux 自动连接无限,hotplug应用实例：自动连接无线网

發布時間：2023/12/10 linux 43 豆豆

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Linux內核提供了一種機制，使得有熱插拔事件(比如插入或拔出U盤)發生時可以執行一個程序，在本文中我稱之為hotplug程序。內核在調用

hotplug程序時會傳遞一個命令行參數，這個參數是發生熱插拔事件的子系統名稱，常見的有usb, module, drivers,

net等。此外內核在調用hotplug程序是還會設置一些環境變量，如SUBSYSTEM, ACTION, PRODUCT, TYPE,

INTERFACE, DEVPATH等。

下面是一系列實際的熱插拔事件的例子，每一行表示hotplug程序被調用一次：

1 SUBSYSTEM=net, ACTION=linkup, PRODUCT=, TYPE=, INTERFACE=eth0, DEVPATH=/class/net/eth0

2 SUBSYSTEM=module, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/module/ehci_hcd

3 SUBSYSTEM=platform, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/devices/platform/ehci_hcd

4 SUBSYSTEM=drivers, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/bus/platform/drivers/ehci_hcd

5 SUBSYSTEM=usb_host, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/class/usb_host/usb1

6 SUBSYSTEM=usb, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/devices/platform/ehci_hcd/usb1

7 SUBSYSTEM=module, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/module/ohci_hcd

8 SUBSYSTEM=platform, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/devices/platform/ohci_hcd

9 SUBSYSTEM=drivers, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/bus/platform/drivers/ohci_hcd

10 SUBSYSTEM=usb_host, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/class/usb_host/usb2

11 SUBSYSTEM=usb, ACTION=add, PRODUCT=0/0/206, TYPE=9/0/1, INTERFACE=9/0/0, DEVPATH=/devices/platform/ehci_hcd/usb1/1-0:1.0

12 SUBSYSTEM=usb, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/devices/platform/ohci_hcd/usb2

13 SUBSYSTEM=scsi_host, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/class/scsi_host/host0

14 SUBSYSTEM=usb, ACTION=add, PRODUCT=18a5/216/112, TYPE=0/0/0, INTERFACE=8/6/80, DEVPATH=/devices/platform/ehci_hcd/usb1/1-1/1-1:1.0

15 SUBSYSTEM=usb, ACTION=add, PRODUCT=0/0/206, TYPE=9/0/0, INTERFACE=9/0/0, DEVPATH=/devices/platform/ohci_hcd/usb2/2-0:1.0

16 SUBSYSTEM=usb, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/devices/platform/ehci_hcd/usb1/1-1

17 SUBSYSTEM=scsi_generic, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/class/scsi_generic/sg0

18 SUBSYSTEM=scsi_device, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/class/scsi_device/0:0:0:0

19 SUBSYSTEM=scsi, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/devices/platform/ehci_hcd/usb1/1-1/1-1:1.0/host0/target0:0:0/0:0:0:0

20 SUBSYSTEM=block, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/block/sda

21 SUBSYSTEM=module, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/module/ufsd

22 SUBSYSTEM=block, ACTION=add, PRODUCT=, TYPE=, INTERFACE=, DEVPATH=/block/sda/sda1

系統默認的熱插拔處理程序是/sbin/hotplug。在MP800H上/sbin/hotplug用的是diethotplug-0.4，在華

碩公開的源碼中有它的源代碼。這是一個瘦身版的hotplug程序，它的主要工作是在usb存儲設備插入時進行自動掛載，掛載目錄在/tmp

/usbmounts下面，如/tmp/usbmounts/sda1。

我們可以通過修改/proc/sys/kernel/hotplug來重新指定hotplug程序，通過定制hotplug程序，我們可以按我們希望的方式來處理熱插拔事件，比如插入無線網卡時自動連接無線網。下面我將給出一個實現此功能的程序實例。

程序由兩個shell腳本和一個配置文件組成：hotplug腳本是我們定制的hotplug程序，wifi_monitor腳本是無線網絡監控程

序，它們都放在/usr/local/sbin下。wifi.conf是無線網絡配置文件，放在/usr/local/etc下。

首先用我們的hotplug程序替換系統默認的/sbin/hotplug

$ echo /usr/local/sbin/hotplug > /proc/sys/kernel/hotplug

程序是這樣工作的：熱插拔事件發生時，內核執行我們的hotplug程序，即/usr/local/sbin/hotplug。hotplug程序先調用

/sbin/hotplug，讓它完成它該做的工作。然后判斷該事件是否為usb無線網卡插入事件，如果是則執行wifi_monitor，如果是無線網

絡連接事件則通過DHCP獲取IP地址。wifi_monitor根據wifi.conf配置文件嘗試連接無線網絡。它先掃描可用無線網絡，如果找到指定

的網絡則進行連接，否則等5秒鐘再重新掃描。如果掃描3次都沒有找到，則等待10秒鐘后重新讀入配置文件再次開始掃描循環。wifi_monitor還可

以處理無線網絡斷線的情況，即發現無線網絡斷開時重新開始掃描循環。

/usr/local/sbin/hotplug

#!/bin/sh

# let /sbin/hotplug do the dirty work first

/sbin/hotplug $1

#define log file. set to /dev/null if you want to suppress logging

LOG=/var/log/hotplug.log

# log the event

echo "[`date`] hotplug SUBSYSTEM=$SUBSYSTEM, ACTION=$ACTION, PRODUCT=$PRODUCT, TYPE=$TYPE, INTERFACE=$INTERFACE, DEVPATH=$DEVPATH" >> $LOG

EVENT="$SUBSYSTEM.$INTERFACE.$ACTION";

if [ "$EVENT" = "net.wlan0.add" ] ; then

# start wifi monitor

/usr/local/sbin/wifi_monitor $INTERFACE &

elif [ "$EVENT" = "net.wlan0.linkup" ] ; then

/sbin/udhcpc -i $INTERFACE -t 15 -b -q -s /etc/udhcpc.script >> $LOG 2>&1

/usr/local/sbin/wifi_monitor

#!/bin/sh

PATH=/sbin:/usr/sbin:/bin:/usr/bin:/usr/local/sbin:/usr/local/bin

WPA_CTRL_INTERFACE=/var/lock/wpa_supplicant

WPA_SUPPLICANT_PID=/var/lock/wpa_supplicant.pid

WPA_SUPPLICANT_CONF=/tmp/wpa_supplicant.conf

WIFI_CONF=/usr/local/etc/wifi.conf

if [ -z "$1" ] ; then

echo "Usage: wifi_monitor "

exit 1

IFACE=$1

PIDFILE=/var/lock/wifi_monitor.$IFACE.pid

SYSFS="/sys/class/net/$IFACE"

if [ -e $PIDFILE ] && grep -q wifi_monitor /proc/`cat $PIDFILE`/cmdline ; then

echo "wifi_monitor: another instance is running, quiting..."

exit

read_conf() {

for v in ESSID SECURITY WEP_AUTH WEP_KEYINDEX WEP_KEY WPA_PASSPHRASE ; do unset CONF_$v ; done

for line in `grep -E '^ *[A-Z_]+ *= *[^ #]+' $WIFI_CONF|sed -e 's/#.*//' -e 's/ *//g'` ; do eval CONF_$line ; done

}

reload() {

echo "wifi_monitor: reloading..."

ifconfig $IFACE down

iwconfig $IFACE essid off

}

quit() { exit; }

cleanup() {

[ -e $WPA_SUPPLICANT_PID ] && pkill -x wpa_supplicant

rm -f $WPA_SUPPLICANT_PID

rm -rf $WPA_CTRL_INTERFACE

rm -f $PIDFILE

}

setup_wifi() {

[ -n "$CONF_ESSID" ] || { echo "Error: ESSID not defined!" ; return; }

# scan for AP

ifconfig $IFACE up

local count=0

until [ $count -ge 3 ] || iwlist $IFACE scanning|grep -q $CONF_ESSID ;

echo "AP $CONF_ESSID not found, sleeping...";

sleep 5;

let 'count=count+1';

done

if [ $count -lt 3 ] ; then

[ "x$CONF_SECURITY" != "xWPA" ] && [ -e $WPA_SUPPLICANT_PID ] && kill `cat $WPA_SUPPLICANT_PID`

case "$CONF_SECURITY" in

NONE)

iwconfig $IFACE key off

iwconfig $IFACE essid "$CONF_ESSID"

;;

WEP)

[ -n "$CONF_WEP_KEY" ] || { echo "Error: WEP_KEY not defined!" ; return; }

if [ -n "$CONF_WEP_KEYINDEX" ] ; then

iwconfig $IFACE key $CONF_WEP_AUTH [$CONF_WEP_KEYINDEX] "$CONF_WEP_KEY"

else

iwconfig $IFACE key $CONF_WEP_AUTH "$CONF_WEP_KEY"

iwconfig $IFACE essid "$CONF_ESSID"

;;

WPA)

[ -n "$CONF_WPA_PASSPHRASE" ] || { echo "Error: WPA_PASSPHRASE not defined!" ; return; }

if [ ! -e $WPA_SUPPLICANT_PID ] || ! pgrep -x wpa_supplicant > /dev/null ; then

# generate the wpa_supplicant.conf

if [ "x$LAST_WPA_PASSPHRASE" != "x$CONF_ESSID.$CONF_WPA_PASSPHRASE" ] ; then

WPA_PSK=`wpa_passphrase "$CONF_ESSID" "$CONF_WPA_PASSPHRASE"|grep -o 'psk=[0-9a-z]\{64\}'`

LAST_WPA_PASSPHRASE="$CONF_ESSID.$CONF_WPA_PASSPHRASE"

cat >$WPA_SUPPLICANT_CONF<

ctrl_interface=$WPA_CTRL_INTERFACE

network={

ssid="$CONF_ESSID"

scan_ssid=1

proto=WPA RSN

key_mgmt=WPA-PSK

pairwise=CCMP TKIP

group=CCMP TKIP

$WPA_PSK

}

EOF

wpa_supplicant -B -Dwext -i$IFACE -c$WPA_SUPPLICANT_CONF -P$WPA_SUPPLICANT_PID

;;

esac

}

trap 'reload' HUP

trap 'quit' INT QUIT TERM

trap 'cleanup' EXIT

echo $$ > $PIDFILE

# wait until the kernel structure is ready. FIXME: Is this really necessary?

until [ -d $SYSFS ] ; do sleep 1; done

while [ -d $SYSFS ] ; do

carrier=`cat $SYSFS/carrier 2>/dev/null`

if [ "x$carrier" != "x1" ] ; then

# reload configuration

read_conf

setup_wifi

sleep 10

done

/usr/local/etc/wifi.conf - WEP實例

ESSID=MYESSID

# wireless security: NONE, WEP or WPA

SECURITY=WEP

# WEP security mode: open or restricted

WEP_AUTH=restricted

WEP_KEYINDEX=1

WEP_KEY="06af3154902d96506b3cbe6bae"

/usr/local/etc/wifi.conf - WPA實例

ESSID=MYESSID

# wireless security: NONE, WEP or WPA

SECURITY=WPA

WPA_PASSPHRASE="testtest"

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