ifupdown problem

[Martin Townsend]

Hi Denys,

On Tue, Sep 20, 2016 at 4:34 PM, Denys Vlasenko
<vda.linux at googlemail.com> wrote:
> On Tue, Sep 6, 2016 at 3:11 PM, Martin Townsend <mtownsend1973 at gmail.com> wrote:
>> Hi,
>>
>> I'm using busybox with ENABLE_FEATURE_IFUPDOWN_IP and when using
>> ifdown with a virtual interface it takes down the primary interface as
>> well.  For our board we setup eth0:0 on a 10.10.10.x/29 network and
>> using ifup eth0:0 does the following:
>> ip addr add 10.10.10.9/29 dev eth0:0 label eth0:0
>> ip link set eth0:0 up
>> run-parts /etc/network/if-up.d
>>
>> and ip addr show gives us
>> ...
>> 2 : eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
>> state UP group default qlen 1000
>>     link/ether a0:f6:fd:18:2b:13 brd ff:ff:ff:ff:ff:ff
>>     inet 172.27.105.10/22 brd 172.27.107.255 scope global eth0
>>        valid_lft forever preferred_lft forever
>>     inet 10.10.10.9/29 scope global eth0:0
>>        valid_lft forever preferred_lft forever
>>     inet6 fe80::a2f6:fdff:fe18:2b13/64 scope link
>>        valid_lft forever preferred_lft forever
>>
>>
>> Taking it down runs
>>
>> ip addr flush dev eth0:0
>> ip link set eth0:0 down
>> run-parts /etc/network/if-post-down.d
>>
>> The problem is ip addr flush dev eth0:0 removes all ip addresses from
>> eth0.  You can see this if you run
>> ip -stat -stat addr flush dev eth0:0
>>
>> 2: eth0    inet 172.27.105.10/22 brd 172.27.107.255 scope global eth0
>>        valid_lft forever preferred_lft forever
>> 2: eth0    inet 10.10.10.9/29 scope global eth0:0
>>        valid_lft forever preferred_lft forever
>> 2: eth0    inet6 fe80::a2f6:fdff:fe18:2b13/64 scope link
>>        valid_lft forever preferred_lft forever
>>
>> *** Round 1, deleting 3 addresses ***
>> *** Flush is complete after 1 round ***
>>
>> To work around this I have added the following patch which adds a
>> label to the flush command so only flush the eth0:0 address:
>>
>> As I'm no networking expert is this a valid fix? if not what's the
>> correct way to handle virtual interfaces.
>>
>> I've also tried the switch to use ifconfig and this also fails for a
>> completely different reason and it's because you can't run 'if config
>> eth0:0 up' before using ifconfig eth0:0 10.10.10.9 etc.."
>> You get "SIOCSIFFLAGS: Cannot assign requested address".  As it
>> attempts to run all commands you do actually get the interface and if
>> you run ifup eth0:0 again it will work.  I see there is a reason for
>> running the commands in this order so I don't know what the fix would
>> be for this one.
>>
>> Best Regards,
>> Martin.
>>
>> Index: busybox-1.24.1/networking/ifupdown.c
>> ===================================================================
>> --- busybox-1.24.1.orig/networking/ifupdown.c 2016-09-06
>> 13:39:03.264378441 +0100
>> +++ busybox-1.24.1/networking/ifupdown.c 2016-09-06 13:39:59.288380571 +0100
>> @@ -501,7 +501,7 @@
>>  {
>>   int result;
>>  # if ENABLE_FEATURE_IFUPDOWN_IP
>> - result = execute("ip addr flush dev %iface%", ifd, exec);
>> + result = execute("ip addr flush dev %iface% [[ label %label%]]", ifd, exec);
>>   result += execute("ip link set %iface% down", ifd, exec);
>>  # else
>>   /* result = execute("[[route del default gw %gateway% %iface%]]",
>> ifd, exec); */
>
> This looks correct, applied to git.
>
> However, the entire ifup/down thing is a bad idea.
> It's too inflexible. I suggest using something else.

I'm using ifplugd which uses ifup/down it does seem to now work but
out of interest what are the alternatives? and I will take a look at
them as I have to support an Ethernet gadget interface soon so I have
the option of moving to something different.

Cheers,
Martin.