[PATCH] eth-multiplxer: Implement ds_device_close()

[Joan Lledó]

Hello,

One difference between pfinet and lwip translators is that pfinet doesn't 
delete interfaces (or I haven't found how to do it) while lwip does. For 
instance, if one starts pfinet with:

settrans -fga /servers/socket/2 /hurd/pfinet -i /dev/eth1 -a 192.168.123.178 -m 
255.255.255.0 -g 192.168.123.1

and then runs:

fsysopts /servers/socket/2 --interface=/dev/eth2 --address=192.168.124.178 
--netmask=255.255.255.0 --gateway=192.168.124.1

the result is this:

root@hurd:/home/jlledom# fsysopts /servers/socket/2
/hurd/pfinet --interface=/dev/eth1 --address=192.168.123.178 
--netmask=255.255.255.0 --address6=fc00:123::5054:ff:feb6:1ab3/64 
--address6=fe80::5254:b6:1ab3/10 --address6=fe80::5054:ff:feb6:1ab3/10 
--gateway6=fe80::5054:ff:fef6:d496 --interface=/dev/eth2 
--address=192.168.124.178 --netmask=255.255.255.0 --gateway=192.168.124.1 
--address6=fe80::5254:4b:ad11/10 --address6=fe80::5054:ff:fe4b:ad11/10

fsysopts added a new interface. But doing the same with lwip leads to this:

root@hurd:/home/jlledom# fsysopts /servers/socket/2
/hurd/lwip --interface=/dev/eth2 --address=192.168.124.178 
--netmask=255.255.255.0 --gateway=192.168.124.1 
--address6=FE80::5054:FF:FE4B:AD11/64 --address6=FC00:124::5054:FF:FE4B:AD11/64

The stack is reset and reconfigured, and only the given interface is added. I 
implemented this by simply removing all interfaces anytime somebody calls 
fsysopts, and adding the new ones. If some interface already exists, it's 
deleted and created again.

This behaviour generated a problem when working with eth-multiplexer. Adding a 
new interface calls ds_device_open in eth-multiplexer and that returns a port 
name, whereas deleting the interface deallocates the port name in lwip, but 
nothing happens in eth-multiplexer since ds_device_close is unimplemented, when 
lwip tries to create the same interface again, eth-multiplexer returns the same 
port name, and trying to use it leads to a MIG_SERVER_DIED error. This use to 
happen when ifupdown uses dhclient to get an address and is not a problem in 
pfinet since it doesn't remove the interface.

I wrote a little patch to implement ds_device_close(). This patch is working 
for me, but I'm not sure whether it's the right way to do it or may affect 
other servers. I'd appreciate some feedback.

Regards,

Joan