linux内核态获取ip地址,嵌入式linux通过DHCP自动获取IP地址

虽然还不太懂，但先记录摸索过程，后续懂了再来完善。

1．编译内核选项

在内核中添加以下选项：

Networking --->

[*]

Networking

support

Networking options --->

Packet socket //添加.配置CONFIG_PACKET

[ *

] IP: DHCP

support //添加

[ * ] Network packet filtering (replaces

ipchains) ---> //添加，后面子选项可不选，配置CONFIG_NETFILTER

说明：若没选 Packet

socket, [ * ] Network packet filtering (replaces

ipchains) --->选项，在执行udhcpc命令时出现如下错误：

#

udhcpc

udhcpc (v0.9.9-pre)

started

udhcpc[208]: udhcpc

(v0.9.9-pre) started

FATAL: couldn't

listen on socket, Address family not supported by

protocol

udhcpc[208]: FATAL:

couldn't listen on socket, Address family not supported by

protocol

2．编译udhcpc

Busybox中添加以下选项：

Networking

Utilities

--->

udhcp

Server/Client --->

[] udhcp Server

(udhcpd) //在此不作服务端，故不选。生成udhcpd命令

[*] udhcp Client

(udhcpc) //生成udhcpc命令

[ ] Lease display utility

(dumpleases)

[ ] Log udhcp messages to

syslog (instead of

stdout)

[ ] Compile udhcp with noisy

debugging messages

若busybox没编译相应选项，也可从网上下载相应文件，用arm-linux交叉编译得到udhcpd,udhcpc命令copy到usr/sbin下就可以了。

我从网上下的udhcp_0.9.8cvs20050303.orig.tar.gz文件，解压后修改Makefile文件。在19行添加CROSS_COMPILE=arm-linux-，注释12行的COMBINED_BINARY=1，否则不生成udhcpc命令。

3．建相关配置文件

在文件/usr/share/udhcpc/default.script下编写脚本程序

#!/bin/sh

exec run-parts -a

"$1" /etc/udhcpc.d

//运行此目录下的所有程序

在/etc/udhcpc.d/50default文件中编写如下代码：

#!/bin/sh

# udhcpc script

edited by Tim Riker

[ -z "$1" ]

&& echo "Error: should be called from udhcpc" &&

exit 1

RESOLV_CONF="/etc/resolv.conf"

[ -n "$broadcast" ]

&& BROADCAST="broadcast $broadcast"

[ -n "$subnet" ]

&& NETMASK="netmask $subnet"

# return 0 if root

is mounted on a network filesystem

root_is_nfs()

{

sed -n 's/^[^ ]* $[^ ]*$ $[^ ]*$ .*$/\1 \2/p' /proc/mounts

|

grep -q "^/ $nfs\|smbfs\|ncp\|coda$$"

}

have_bin_ip=0

if [ -x /sbin/ip ];

then

have_bin_ip=1

fi

case "$1"

in

deconfig)

if [ -x /sbin/resolvconf ]; then

/sbin/resolvconf -d "${interface}.udhcpc"

fi

if ! root_is_nfs ; then

if [ $have_bin_ip -eq 1 ]; then

ip addr flush dev $interface

ip link set dev $interface up

else

/sbin/ifconfig $interface 0.0.0.0

fi

fi

;;

renew|bound)

if [ $have_bin_ip -eq 1 ]; then

ip addr add dev $interface local $ip/$mask

$BROADCAST

else

/sbin/ifconfig $interface $ip $BROADCAST $NETMASK

fi

if [ -n "$router" ] ; then

if

! root_is_nfs ; then

if [ $have_bin_ip -eq 1 ]; then

while ip route del default 2>/dev/null ; do

:

done

else

while route del default gw 0.0.0.0 dev $interface 2>/dev/null ;

do

:

done

fi

fi

metric=0

for i in $router ; do

if [ $have_bin_ip -eq 1 ]; then

ip route add default via $i metric $metric

else

route add default gw $i dev $interface metric $metric

2>/dev/null

fi

metric=$(($metric + 1))

done

fi

# Update resolver configuration file

R=""

[ -n "$domain" ] && R="domain $domain"

for i in $dns; do

echo "$0: Adding DNS $i"

R="${R}nameserver

$i"

done

if [ -x /sbin/resolvconf ]; then

echo -n "$R" | /sbin/resolvconf -a

"${interface}.udhcpc"

else

echo -n "$R" > "$RESOLV_CONF"

fi

;;

esac

exit

0

4．/etc/rc5.d中有一个关于网络的启动文件，当嵌入式Linux启动时会进入rc5.d文件执行(因为inittab文件中The default runlevel=5)。其中网络启动脚本S01networking如下：

root@am335x-evm:/etc/rc5.d# cat

S01networking

#!/bin/sh

#

### BEGIN INIT

INFO

#

Provides: networking

#

Required-Start: $local_fs mountvirtfs

#

Required-Stop: $local_fs

#

Default-Start: S

#

Default-Stop: 0 6

#

Short-Description: Raise network interfaces and configure

them

### END INIT

INFO

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

if ! [ -x

/sbin/ifup ]; then

exit 0

fi

case "$1"

in

start)

if sed -n 's/^[^ ]* $[^ ]*$ $[^ ]*$ .*$/\1 \2/p' /proc/mounts

|

grep -q "^/ nfs$"; then

echo "NOT configuring network interfaces: / is an NFS

mount"

elif sed -n 's/^[^ ]* $[^ ]*$ $[^ ]*$ .*$/\1 \2/p' /proc/mounts

|

grep -q "^/ smbfs$"; then

echo "NOT configuring network interfaces: / is an SMB

mount"

elif sed -n 's/^[^ ]* $[^ ]*$ $[^ ]*$ .*$/\2/p' /proc/mounts

|

grep -qE '^(nfs|smbfs|ncp|coda)$'; then

echo "NOT configuring network interfaces: network shares still

mounted."

else

echo -n "Configuring network interfaces... "

ifup -a

echo "done."

fi

;;

stop)

if sed -n 's/^[^ ]* $[^ ]*$ $[^ ]*$ .*$/\1 \2/p' /proc/mounts

|

grep -q "^/ nfs$"; then

echo "NOT deconfiguring network interfaces: / is an NFS

mount"

elif sed -n 's/^[^ ]* $[^ ]*$ $[^ ]*$ .*$/\1 \2/p' /proc/mounts

|

grep -q "^/ smbfs$"; then

echo "NOT deconfiguring network interfaces: / is an SMB

mount"

elif sed -n 's/^[^ ]* $[^ ]*$ $[^ ]*$ .*$/\2/p' /proc/mounts

|

grep -qE

'^(nfs|smbfs|ncp|coda)$'; then

echo "NOT deconfiguring network interfaces: network shares still

mounted."

else

echo -n "Deconfiguring network interfaces... "

ifdown -a

echo "done."

fi

;;

force-reload|restart)

echo -n "Reconfiguring network interfaces... "

ifdown -a

ifup -a

echo "done."

;;

*)

echo "Usage: /etc/init.d/networking

{start|stop|restart|force-reload}"

exit 1

;;

esac

exit

0

执行此脚本和执行 /etc/init.d/networking是一样的，包括start|stop|restart|force-reload。

其中，ifup -a 会执行/etc/network/interfaces程序(If given to ifup, affect

all interfaces marked auto.

Interfaces are brought up in the order in which they are defined

in)。

/etc/network/interfaces下的程序如下所示，应该是声明和启动各种类型的网卡。我这里使用eth0，初始声明为静态static，后面根据配置参数在选择是动态分配dhcp还是静态分配static。

root@am335x-evm:/etc/rc5.d# cat

/etc/network/interfaces

#

/etc/network/interfaces -- configuration file for ifup(8),

ifdown(8)

# The loopback

interface

auto

lo

iface lo inet

loopback

# Wireless

interfaces

iface wlan0 inet

dhcp

wireless_mode managed

wireless_essid any

wpa-driver wext

wpa-conf /etc/wpa_supplicant.conf

iface tiwlan0 inet

dhcp

wireless_mode managed

wireless_essid any

iface atml0 inet

dhcp

# Wired or wireless

interfaces

auto

eth0

iface eth0 inet

static

# pre-up /bin/grep -v -e "ip=[0-9]\+\.[0-9]\+\.[0-9]\+\.[0-9]\+"

/proc/cmdline > /dev/null

iface eth1 inet

dhcp

# Ethernet/RNDIS

gadget (g_ether)

# ... or on host

side, usbnet and random hwaddr

iface usb0 inet

dhcp

# Bluetooth

networking

iface bnep0 inet

dhcp

#dns-nameservers

114.114.114.114 8.8.8.8

可直接在此文件中配置动态分配dhcp和静态分配static，以及DNS等。配置方法如下：

Ø

以DHCP方式配置网卡

auto eth0

iface eth0 inet dhcp

Ø

为网卡配置静态IP地址

auto eth0

iface eth0 inet static

address 192.168.3.90

gateway 192.168.3.1

netmask 255.255.255.0

#network 192.168.3.0

#broadcast 192.168.3.255

我根据用户配置文件来选择动态还是静态，当选择动态dhcp分配时，使用如下命令：

root@am335x-evm:/etc/rc5.d# udhcpc -b -i eth0 -p

/var/run/udhcpc.Rpid

udhcpc (v1.22.1)

started

Sending

discover...

Sending select for

188.188.181.175...

Lease of

188.188.181.175 obtained, lease time 86400

/etc/udhcpc.d/50default: Adding DNS

202.96.209.5

/etc/udhcpc.d/50default: Adding DNS

202.96.209.133

注：解释一下，-b就是切换到后台指令，-i是指定使用哪个网络接口，双网卡的时候一定要使用它来指定eth0 or

eth1。

udhcpc -R -q 退出DHCP并且释放IP地址。

root@am335x-evm:/etc/rc5.d# udhcpc -R

-q

udhcpc (v1.22.1)

started

Sending

discover...

Sending select for

188.188.181.175...

Lease of

188.188.181.175 obtained, lease time 86400

/etc/udhcpc.d/50default: Adding DNS

202.96.209.5

/etc/udhcpc.d/50default: Adding DNS

202.96.209.133

Unicasting a

release of 188.188.181.175 to 188.188.181.1

Sending

release...

Entering released

state

系统启动后，当用户选择静态分配IP时，使用ifconfig和route来设置IP地址、掩码地址和网关地址，并在/etc/resolv.conf文件中写入dns解析地址，这样就可以ping通百度了。

echo nameserver

114.114.114.114 > /etc/resolv.conf

echo nameserver

8.8.8.8 >> /etc/resolv.conf

ifconfig eth0

$gateway_ip netmask $gateway_mk

route add default

gw $gateway_gw

参考文章：