【linux】network服务启动网卡流程

1、介绍

network服务的核心由/etc/sysconfig/network-scripts/下一堆脚本配置来生效，其中启动网卡就是通过ifup脚本来实现的，下面就讲一下ifup如何恢复ip和route的流程。

2、ifup流程

【1】与NetworkManager兼容

ifup有一段内容为如果网卡被NetworkManager接管就通过nmcli去激活连接，内容如下：

if is_true "$_use_nm" && [ -n "$UUID" ] && [ "$REALDEVICE" != "lo" ]; then
    if [ "foo$2" = "fooboot" ] && [ "${TYPE}" = "Wireless" ]; then
        exit 0
    fi
    [ -n "${DEVICE}" ] && is_nm_handling ${DEVICE} && exit 0
    echo ${DEVICE} ${UUID}
    nmcli con up uuid "$UUID" #通过nmcli去激活连接
    exit $?
fi

否则就会走到对应接口类型的脚本中去，比如以太网就会执行ifup-eth，内容如下：

OTHERSCRIPT="/etc/sysconfig/network-scripts/ifup-${DEVICETYPE}"

if [ ! -x ${OTHERSCRIPT} ]; then
    OTHERSCRIPT="/etc/sysconfig/network-scripts/ifup-${TYPE}"
fi

if [ ! -x ${OTHERSCRIPT} ]; then
    OTHERSCRIPT="/etc/sysconfig/network-scripts/ifup-eth" #以太网接口对应的脚本
fi

exec ${OTHERSCRIPT} ${CONFIG} $2

【2】ifup-eth设置ip

网卡上的ip设置就是通过ifup-eth来设置的，读取ifcfg-xxx配置，通过ip addr add设置，内容如下：

if ! ip addr add ${ipaddr[$idx]}/${prefix[$idx]} \
    brd ${broadcast[$idx]:-+} dev ${REALDEVICE} ${SCOPE} label ${DEVICE}; then
    net_log $"Error adding address ${ipaddr[$idx]} for ${DEVICE}."
 else
    echo "ip addr add ${ipaddr[$idx]}/${prefix[$idx]} dev {REALDEVICE}"
 fi

如果ifcfg-xxx中有配置GATEWAY就会去设置默认路由，通过ip route reolace去设置，内容如下：

# Set a default route.
if ! is_false "${DEFROUTE}" && [ -z "${GATEWAYDEV}" -o "${GATEWAYDEV}" = "${REALDEVICE}" ]; then
    # set up default gateway. replace if one already exists
    if [ -n "${GATEWAY}" ] && [ "$(ipcalc --network ${GATEWAY} ${netmask[0]} 2>/dev/null)" = "NETWORK=${NETWORK}" ]; then
       	ip route replace default ${METRIC:+metric $METRIC} \
        ${EXTRA_ROUTE_OPTS} \
        via ${GATEWAY} ${WINDOW:+window $WINDOW} ${SRC} \
        ${GATEWAYDEV:+dev $GATEWAYDEV} ||
        net_log $"Error adding default gateway ${GATEWAY} for ${DEVICE}."
    elif [ "${GATEWAYDEV}" = "${DEVICE}" ]; then
        ip route replace default ${METRIC:+metric $METRIC} \
        ${EXTRA_ROUTE_OPTS} \
        ${SRC} ${WINDOW:+window $WINDOW} dev ${REALDEVICE} ||
        net_log $"Error adding default gateway for ${REALDEVICE}."
    fi
fi

【3】ifup-routes设置路由

网卡上的路由恢复是通过ifup-routes来设置的，读去route-xxx的配置，通过ip route add设置，根据不同的格式执行不同的函数，内容如下：

handle_file () {
    . $1
    routenum=0
    while [ "x$(eval echo '$'ADDRESS$routenum)x" != "xx" ]; do
        eval $(ipcalc -p $(eval echo '$'ADDRESS$routenum) $(eval echo '$'NETMASK$routenum))
        line="$(eval echo '$'ADDRESS$routenum)/$PREFIX"
        if [ "x$(eval echo '$'GATEWAY$routenum)x" != "xx" ]; then
            line="$line via $(eval echo '$'GATEWAY$routenum)"
        fi
        line="$line dev $2"
        echo $line
        /sbin/ip route add $line #设置路由
        routenum=$(($routenum+1))
    done
}

handle_ip_file() {
    local f t type= file=$1 proto="-4"
    f=${file##*/}
    t=${f%%-*}
    type=${t%%6}
    if [ "$type" != "$t" ]; then
        proto="-6"
    fi
    { cat "$file" ; echo ; } | while read line; do
        if [[ ! "$line" =~ $MATCH ]]; then
            echo $proto $type $line     
            /sbin/ip $proto $type add $line #设置路由
        fi
    done
}

FILES="/etc/sysconfig/network-scripts/route-$1 /etc/sysconfig/network-scripts/route6-$1"
if [ -n "$2" -a "$2" != "$1" ]; then
    FILES="$FILES /etc/sysconfig/network-scripts/route-$2 /etc/sysconfig/network-scripts/route6-$2"
fi

for file in $FILES; do
    if [ -f "$file" ]; then
        if grep -Eq '^[[:space:]]*ADDRESS[0-9]+=' $file ; then
            # new format
            handle_file $file ${1%:*}
        else
            # older format
            handle_ip_file $file
        fi
    fi
done