ref: c690c0b9f3074708f33c4d982e26b67de1dfcb95
dir: /rc/bin/ethermultilink/
#!/bin/rc
# ethermultilink outpus bridge(3) commands to switch
# between multiple ethernet (or wifi) interfaces
# depending on their link status.
# the first argument is the primary interface,
# which is permanently added to the bridge
# while the following arguments are for secondary
# interfaces in increasing priority order.
# only the highest priority active interface is bound.
rfork e
fn usage {
echo 'Usage: ' $0 'primaryether secondaryether1 [secondaryether2 ....] > /net/bridgeX/ctl' >[1=2]
exit 'usage'
}
fn missing {
echo 'missing: ' $1 >[1=2]
exit 'missing'
}
~ $#* 0 1 && usage
# make sure arguments are ethernets
for(i){
test -r $i/stats || missing $i/stats
}
# first interface is the primary
primary=$1
shift
ea=`{cat $primary/addr} || missing $primary/addr
net=`{echo $primary | sed 's!/*[^/]*$!!g'}
test -r $net/arp || missing $net/arp
# insert the primary to bridge
echo bind ether primary 0 $primary || exit
# now select secondary from the list depending on link status
@{
type=none
old=/dev/null
while(){
# interfaces are in increasing priority order
for(i){
if(! ~ $i $primary && grep -s 'link: 1' $i/stats)
secondary=$i
}
if(! ~ $secondary $old){
echo $primary is switching from $old to $secondary >[1=2]
if(! ~ $type none){
echo unbind $type secondary 0
}
# if the secondary has the same ea as the primary,
# we need to bind it in non-bridge mode
type=ether
if(~ $ea `{cat $secondary/addr})
type=ethermac
echo bind $type secondary 0 $secondary
# make switches aware of the new path
echo flush > $net/arp
}
old=$secondary
sleep 1
}
} </dev/null &
exit ''