Get netconsole options to send logs to a given IP.

get_netconsole_options.sh

#!/bin/bash
# gnco.sh: Get netconsole options to send logs to a given IP.
# Author: Joe Stringer
#
# v1.1: Minor script tidyups.
# v1.0: Initial post.

# $1: L3 destination
function get_l2()
{
    ping -c 1 $1 > /dev/null
    arp -n $1 | tail -n 1 | sed 's/  */ /g' | cut -d' ' -f3
}

# $1: Output of 'ip route get foo'
# $2: Parameter to search for, eg "via", "dev"
function get_route_param()
{
    EXPR="s/.*\($2 [^ ]*\)/\1/"

    echo $1 | sed -e "$EXPR" -e 's/  */ /' | cut -d' ' -f2
}

# $1: MAC address
function is_mac_valid()
{
    echo $1 | grep ":" 2>&1>/dev/null
}

function main()
{
    if [ $# -lt 1 ] || [ $# -gt 1 ]; then
        echo "Usage: $0 <dst-ip>"
        exit 1;
    fi

    L2_DST="???"
    L3_DST=$1
    L4_SRC=6666
    L4_DST=6666
    GATEWAY=$L3_DST
    ROUTE=`ip route get $L3_DST`
    IFACE=`get_route_param "$ROUTE" "dev"`
    L3_SRC=`get_route_param "$ROUTE" "src"`

    if ! echo "$ROUTE" | grep "via" 2>&1>/dev/null; then
        GATEWAY=`get_route_param $ROUTE "via"`
    fi

    L2_DST=`get_l2 $GATEWAY`
    if ! is_mac_valid $L2_DST; then
        # Fall back to default route
        GATEWAY=`netstat -rn | grep ^0.0.0.0 | sed 's/  */ /' | cut -d' ' -f2`
        L2_DST=`get_l2 $GATEWAY`

        if ! is_mac_valid $L2_DST; then
            echo "Couldn't resolve gateway '$GATEWAY'" 1>&2
            exit 1
        fi
    fi

    echo netconsole=${L4_SRC}@${L3_SRC}/${IFACE},${L4_DST}@${L3_DST}/${L2_DST}
}

main $*