深入linux系统network服务机制

通过查看centos5系统下/etc/sysconfig/network-scripts/network-functions文件，了解linux系统network服务机制和原理。（对设置双线路由，添加新网卡都是有帮助的）。
系统是不断更新的，原理是老成的，当你遇到老系统添加新硬件时，还是掌握系统原理最主要。
以下是network-functions配置文件内容。我会重要的地方加载红色注释。

# -*-Shell-script-*-
#
# This file is not a stand-alone shell script; it provides functions
# to network scripts that source it.

# Set up a default search path.
PATH="/sbin:/usr/sbin:/bin:/usr/bin"
export PATH

[ -z "$__sed_discard_ignored_files" ] && . /etc/init.d/functions

get_hwaddr ()得到网卡mac地址信息的文件和目录
{
    if [ -f /sys/class/net/${1}/address ]; then
    awk '{ print toupper($0) }' < /sys/class/net/${1}/address
    elif [ -d "/sys/class/net/${1}" ]; then
    LC_ALL= LANG= ip -o link show ${1} 2>/dev/null | \
              awk '{ print toupper(gensub(/.*link\/[^ ]* ([[:alnum:]:]*).*/,
                    "\\1", 1)); }'
    fi
}

get_config_by_hwaddr ()配置MAC地址的文件和目录
{
    LANG=C grep -il "^[[:space:]]*HWADDR=${1}\([[:space:]#]\|$\)" /etc/sysconfig/network-scripts/ifcfg-* \
    | LC_ALL=C sed -e "$__sed_discard_ignored_files"
}

get_config_by_subchannel ()
{
    LANG=C grep -il "^[[:space:]]*SUBCHANNELS=${1}\([[:space:]#]\|$\|,\)" /etc/sysconfig/network-scripts/ifcfg-* \
    | LC_ALL=C sed -e "$__sed_discard_ignored_files"
}

get_device_by_hwaddr ()获得网卡设备信息
{
    LANG=C ip -o link | grep -v link/ieee802.11 | awk -F ': ' -vIGNORECASE=1 "/$1/ { print \$2 }"
}

need_config ()
{
    local nconfig

    CONFIG="ifcfg-${1}"
    [ -f "${CONFIG}" ] && return
    CONFIG="${1}"
    [ -f "${CONFIG}" ] && return
    local addr=`get_hwaddr ${1}`
    if [ -n "$addr" ]; then
      nconfig=`get_config_by_hwaddr ${addr}`
      if [ -n "$nconfig" ] ; then
        CONFIG=${nconfig##*/}
    [ -f "${CONFIG}" ] && return
      fi
    fi
    nconfig=$(LANG=C grep -l "^[[:space:]]*DEVICE=${1}\([[:space:]#]\|$\)" \
    /etc/sysconfig/network-scripts/ifcfg-* \
    | LC_ALL=C sed -e "$__sed_discard_ignored_files")
    if [ -n "$nconfig" -a -f "$nconfig" ]; then
      CONFIG=${nconfig##*/}
      return
    fi
}

source_config ()
{
    DEVNAME=`basename $CONFIG | sed 's/^ifcfg-//g'`
    if echo ${CONFIG##*/} | grep -q '[^g]-' ; then
    PARENTCONFIG=`echo $CONFIG | sed 's/-[^-]*$//g'`
    PARENTDEVNAME=${PARENTCONFIG##*/ifcfg-}
    [ -f $PARENTCONFIG ] || {
        echo $"Missing config file $PARENTCONFIG." >&2
        exit 1
    }
    . $PARENTCONFIG
    [ -r "keys-$PARENTDEVNAME" ] && . keys-$PARENTDEVNAME
    fi
    . $CONFIG
    [ -r "keys-$DEVNAME" ] && . keys-$DEVNAME
    case "$TYPE" in
        Ethernet)
        DEVICETYPE="eth"
        ;;
    CIPE)
        DEVICETYPE="cipcb"
        ;;
    IPSEC)
        DEVICETYPE="ipsec"
        ;;
    Modem)
        DEVICETYPE="ppp"
        ;;
    xDSL)
        DEVICETYPE="ppp"
        ;;
    ISDN)
        DEVICETYPE="ippp"
        ;;
    Wireless)
        DEVICETYPE="eth"
        ;;
    "Token Ring")
        DEVICETYPE="eth"
        ;;
    CTC)
        DEVICETYPE="ctc"
        ;;
    IUCV)
        DEVICETYPE="iucv"
        ;;
    GRE | IPIP)
        DEVICETYPE="tunnel"
        ;;
    esac
    [ -z "$DEVICETYPE" ] && DEVICETYPE=`echo ${DEVICE} | sed "s/[0-9]*$//"`
    [ -z "$REALDEVICE" -a -n "$PARENTDEVICE" ] && REALDEVICE=$PARENTDEVICE
    [ -z "$REALDEVICE" ] && REALDEVICE=${DEVICE%%:*}
    if [ "${DEVICE}" != "${REALDEVICE}" ]; then
        ISALIAS=yes
    else
    ISALIAS=no
    fi
    if [ -n "$HWADDR" ]; then
        HWADDR=`echo $HWADDR | awk '{ print toupper($0) }'`
    fi
    if [ -n "$MACADDR" ]; then
        MACADDR=`echo $MACADDR | awk '{ print toupper($0) }'`
    fi
}



expand_config ()
{
    if [ -z "${NETMASK}" ]; then
    eval `/bin/ipcalc --netmask ${IPADDR}`
    fi

    if [ -z "${PREFIX}" ]; then
    eval `/bin/ipcalc --prefix ${IPADDR} ${NETMASK}`
    fi

    if [ -z "${BROADCAST}" ]; then
    eval `/bin/ipcalc --broadcast ${IPADDR} ${NETMASK}`
    fi

    if [ -z "${NETWORK}" ]; then
    eval `/bin/ipcalc --network ${IPADDR} ${NETMASK}`
    fi
}

toggle_value ()
{
    if [ "$2" = "yes"  -o "$2" = "YES" ] ; then
    echo "$1 on"
    elif [ "$2" = "no"  -o "$2" = "NO" ] ; then
    echo "$1 off"
    else
    echo ''
    fi
}
 
do_netreport ()
{
  # Notify programs that have requested notification
  ( cd /var/run/netreport || exit
    for i in * ; do
      if [ -f $i ]; then
        OWNER=`ls -l $i | awk '{ print $3 }'`
   
        if [ "`id -u`" = "0" ]; then
      su -s /bin/bash $OWNER -c "kill -SIGIO $i >/dev/null 2>&1 || rm -f $i >/dev/null 2>&1" > /dev/null 2>&1
    else
      kill -SIGIO $i >/dev/null 2>&1 || rm -f $i >/dev/null 2>&1
    fi
      fi
    done
  )
}

# rename_device() - Rename a network device to something else
# $1 - desired name
# $2 - hardware address to name (no longer used)
# $3 - '/' separated list of devices that are already in use
#      (for general calls, use the current device you're trying to
#       change to $1)

rename_device()
{
    local target=${3##*/}

    /sbin/ip link set "$target" name "$1" 2>/dev/null || {
      local hw2=`get_hwaddr ${1}`
      local nconfig=`get_config_by_hwaddr ${hw2}`
      local curdev=`get_device_by_hwaddr ${hw2}`
      local dev=
      [ -z "${hw2}" ] && return
      if [ -n "$nconfig"  ]; then
         dev=$(. $nconfig ; echo $DEVICE)
     oldifs=$IFS
     IFS=/
         for device in $3 ; do
        [ "$dev" = "$device" ] && unset dev
         done
     IFS=$oldifs
      fi
      [ -z "$dev" ] && dev=dev$RANDOM
     
      rename_device $dev $hw2 "$3/$curdev"
      /sbin/ip link set "$target" name $1 2>/dev/null
    }
}

# Sets $alias to the device module if $? != 0
is_available ()
{
    LC_ALL= LANG= ip -o link | grep -q $1
    [ "$?" = "1" ] || return 0

    alias=$(modprobe -c | awk \
'BEGIN { alias = ""; }
$1 == "alias" && $2 == "'"$1"'" { alias = $3; }
$1 == "install" { install[$2] = $3; }
END {
    cmd = install[alias];
    print alias;
    if (alias == "" || alias == "off" || cmd == "/bin/true" || cmd == ":")
        exit 1;
    exit 0;
}')
    [ $? -eq 0 ] || return 2

    modprobe $1 > /dev/null 2>&1 || {
      return 1
    }
    if [ -n "$HWADDR" ]; then
       local curdev=`get_device_by_hwaddr "$HWADDR"`
       if [ -z "$curdev" ]; then
          return 1
       fi
       rename_device "$1" "$HWADDR" "$curdev"
    fi

    if [ ${alias} == "bonding" ]; then
    install_bonding_driver $1
    fi

    LC_ALL= LANG= ip -o link | grep -q $1
    return $?
}

need_hostname ()
{
    CHECK_HOSTNAME=`hostname`
    if [ "$CHECK_HOSTNAME" = "(none)" -o "$CHECK_HOSTNAME" = "localhost" -o \
    "$CHECK_HOSTNAME" = "localhost.localdomain" ]; then
    return 0
    else
    return 1
    fi
}

set_hostname ()
{
    hostname $1
    if ! grep search /etc/resolv.conf >/dev/null 2>&1; then
    domain=`echo $1 | sed 's/^[^\.]*\.//'`
    if [ -n "$domain" ]; then
        rsctmp=`mktemp /tmp/XXXXXX`;
        cat /etc/resolv.conf > $rsctmp
        echo "search $domain" >> $rsctmp
        change_resolv_conf $rsctmp
        /bin/rm -f $rsctmp
    fi   
    fi
}

check_device_down ()
{
    if echo $1 | grep -q ':' ; then
     if LC_ALL=C ifconfig -a 2>/dev/null | grep -q $1 ; then
      return 1
     else
      return 0
     fi
    else
     if LC_ALL=C ip -o link 2>/dev/null | grep -q "$1[:@].*,UP" ; then
    return 1
     else
    return 0
     fi
    fi
}

check_mii_tool ()
{
   [ -x /sbin/mii-tool ] || return 2
   output=`LC_ALL=C mii-tool $1 2>&1`
   echo $output | LC_ALL=C grep -q "link ok" && return 1
   echo $output | LC_ALL=C grep -q "no link" && return 0 || return 2
}

check_ethtool ()
{
   [ -x /sbin/ethtool ] || return 2
   output=`LC_ALL=C ethtool $1 2>&1`
   echo $output | LC_ALL=C grep -q "Link detected: yes" && return 1
   echo $output | LC_ALL=C grep -q "Link detected: no" && return 0 || return 2
}


check_link_down ()
{
    if [ -x /sbin/mii-tool -o -x /sbin/ethtool ]; then
        if ! LC_ALL=C ip link show dev $1 2>/dev/null| grep -q UP ; then
       ip link set dev $1 up >/dev/null 2>&1
    fi
    timeout=0
    delay=10
    [ -n "$LINKDELAY" ] && delay=$(($LINKDELAY * 2))
    while [ $timeout -le $delay ]; do
        check_mii_tool $1
        m=$?
        check_ethtool $1
        e=$?
        if [ $m -eq 1 ] || [ $e -eq 1 ] ; then
        return 1
        fi
        if [ $m -eq 2 ] && [ $e -eq 2 ] ; then
        return 1
        fi
        usleep 500000
        timeout=$((timeout+1))
    done
    return 0
    fi
    return 1
}

check_default_route ()
{
    LC_ALL=C ip route list match 0/0 | grep -q default
}

find_gateway_dev ()
{
    . /etc/sysconfig/network
    if [ -n "${GATEWAY}" -a "${GATEWAY}" != "none" ] ; then
    dev=$(LC_ALL=C /sbin/ip route get to "${GATEWAY}" 2>/dev/null | \
        sed -n 's/.* dev \([[:alnum:]]*\) .*/\1/p')
    if [ -n "$dev" ]; then
        GATEWAYDEV="$dev"
        fi
    fi
}

# After the device $1 goes away, restore the standard default route; typically
# used for ppp with DEFROUTE temporarily replacing the "standard" default
# route.
# FIXME: This function doesn't support some newer features (GATEWAY in ifcfg,
# $WINDOW, $METRIC)
add_default_route ()
{
    . /etc/sysconfig/network
    check_default_route && return 0
    find_gateway_dev
    if [ "$GATEWAYDEV" != "" -a -n "${GATEWAY}" -a \
         "${GATEWAY}" != "none" ]; then
        if ! check_device_down $1; then
            if [ "$GATEWAY" = "0.0.0.0" ]; then
                /sbin/ip route add default dev ${GATEWAYDEV}
            else
                /sbin/ip route add default via ${GATEWAY}
            fi
        fi
    elif [ -f /etc/default-routes ]; then
    while read spec; do
        /sbin/ip route add $spec
    done < /etc/default-routes
    rm -f /etc/default-routes
    fi
}

is_wireless_device ()
{
    [ -x /sbin/iwconfig ] || return 1
    LC_ALL=C iwconfig $1 2>&1 | grep -q "no wireless extensions" || return 0
    return 1
}

install_bonding_driver ()
{
   ethtool -i $1 2>/dev/null | grep -q "driver: bonding" && return 0
   [ ! -f /sys/class/net/bonding_masters ] && ( modprobe bonding || return 1 )
   echo "+$1" > /sys/class/net/bonding_masters
   return 0
}

is_bonding_device ()
{
   [ -f "/sys/class/net/$1/bonding/slaves" ]
}

# Invoke this when /etc/resolv.conf has changed:
change_resolv_conf ()
{
    s=`/bin/grep '^[\ \    ]*option' /etc/resolv.conf 2>/dev/null`;
    if [ "x$s" != "x" ]; then
       s="$s"$'\n';
    fi;
    if [ $# -gt 1 ]; then
       let n_args=$#;
       while [ $n_args -gt 0 ];
     do
        if [[ "$s" = *$1* ]]; then
           shift;
           let n_args=n_args-1;
               continue;
            fi;
        s="$s$1";
            shift;
        if [ $# -gt 0 ]; then
        s="$s"$'\n';
        fi;
        let n_args=n_args-1;
         done;      
    elif [ $# -eq 1 ]; then
       if [ "x$s" != "x" ]; then
      s="$s"`/bin/grep -vF "$s" $1`;
       else
      s=`cat $1`;
       fi;
    fi;
    (echo "$s" > /etc/resolv.conf;) >/dev/null 2>&1;
    r=$?
    if [ $r -eq 0 ]; then
    logger -p local7.notice -t "NET" -i "$0 : updated /etc/resolv.conf";
    [ -e /var/lock/subsys/nscd ] && /usr/sbin/nscd -i hosts; # invalidate cache
    fi;
    return $r;
}