为 cable modem 接入配置 LFS network dhcp client

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LFS 可用的 dhcp client 有两个：dhcp 和 dhcpcd，前者包括一个服务器，因为没有必要安装服务，所以我选择后者：
# cat usr/src/dhcpcd/.config

pkgname = "dhcpcd";
version = "1.3.22";
group = "dhcpcd";
user = "dhcpcd";
archive = "dhcpcd-1.3.22-pl4.tar.gz";
patch = "dhcpcd-1.3.22-pl4-fhs-1.patch";
command = "tar xfz dhcpcd-1.3.22-pl4.tar.gz";
command = "cd dhcpcd-1.3.22-pl4";
command = "patch -Np1 -i ../dhcpcd-1.3.22-pl4-fhs-1.patch";
command = "./configure --prefix="" --sysconfdir=/var/lib";
command = "make";
command = "make install";
command = "cd ..";
command = "rm -rf dhcpcd-1.3.22-p14";  
time = "20061125 19:34:15 Sat";

然后安装 blfs-bootscripts-6.1 的 dhcpcd script：
# tar xfj blfs-bootscripts-6.1.tar.bz2
# cd blfs-bootscripts-6.1
# make install-service-dhcpcd
这会在 /etc/sysconfig/network-devices/services 下安装一个 dhcpcd 脚本。

然后移除 /etc/sysconfig/network-devices/ifconfig.eth0/ipv4，编写:
cat > /etc/sysconfig/network-devices/ifconfig.eth0/dhcpcd << "EOF"

ONBOOT="yes"
SERVICE="dhcpcd"
# DHCP_START="[insert appropriate start options here]"
# DHCP_STOP="-k [insert additional stop options here]"
DHCP_STOP="-k"

# Set PRINTIP="yes" to have the script print
# the DHCP assigned IP address
PRINTIP="yes"

# Set PRINTALL="yes" to print the DHCP assigned values for
# IP, SM, DG, and 1st NS. This requires PRINTIP="yes".
PRINTALL="no"
EOF

然后运行 /etc/rc.d/init.d/network restart。

其基本机制是，/etc/rc.d/init.d/network 脚本会首先查找 /etc/sysconfig/network-devices/ifconfig.*，针对每个接口运行 /etc/sysconfig/network-devices/ifup，而这个脚本又会查找所有的配置文件逐一启用，例如 ifconfig.eth0，则会查看 ifconfig.eth0/*，所以如果有 ipv4 和 dhcpcd 则都会运行，所以前面移除 ipv4。对 dhcpcd，则会检查 ONBOOT 和 SERVICE 等参数，对 SERVICE="dhcpcd"，则会寻找 /etc/sysconfig/network-devices/services/dhcpcd 以运行之。