This file is indexed.

/usr/bin/qemu-ifup is in qemu-common 1.0+noroms-0ubuntu13.

This file is owned by root:root, with mode 0o755.

The actual contents of the file can be viewed below.

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#!/bin/sh

nic=$1

if [ -f /etc/default/qemu-kvm ]; then
    . /etc/default/qemu-kvm
fi

if [ -z "$TAPBR" ]; then
    switch=$(ip route list | awk '/^default / { print $5 }')
    if [ ! -d "/sys/class/net/${switch}/bridge" ]; then
        switch=virbr0
    fi
else
    switch=$TAPBR
fi

ifconfig $nic 0.0.0.0 up
brctl addif ${switch} $nic