Subject: Re: [PATCH] bonding: correct the MAC address for "follow" fail_over_mac policy

From: Ding Tianhong <[email-masked]>
Date: Thu, 16 Jul 2015 19:48:07 +0800

On 2015/7/16 17:24, Nikolay Aleksandrov wrote:
> On 07/16/2015 10:30 AM, Ding Tianhong wrote:
>> The "follow" fail_over_mac policy is useful for multiport devices that
>> either become confused or incur a performance penalty when multiple
>> ports are programmed with the same MAC address, but the same MAC
>> address still may happened by this steps for this policy:
>>
>> 1) echo +eth0 > /sys/class/net/bond0/bonding/slaves
>>    bond0 has the same mac address with eth0, it is MAC1.
>>
>> 2) echo +eth1 > /sys/class/net/bond0/bonding/slaves
>>    eth1 is backup, eth1 has MAC2.
>>
>> 3) ifconfig eth0 down
>>    eth1 became active slave, bond will swap MAC for eth0 and eth1,
>>    so eth1 has MAC1, and eth0 has MAC2.
>>
>> 4) ifconfig eth1 down
>>    there is no active slave, and eth1 still has MAC1, eth2 has MAC2.
>>
>> 5) ifconfig eth0 up
>>    the eth0 became active slave again, the bond set eth0 to MAC1.
>>
>> Something wrong here, then if you set eth1 up, the eth0 and eth1 will have the same
>> MAC address, it will break this policy for ACTIVE_BACKUP mode.
>>
>> This patch will fix this problem by finding the old active slave and
>> swap them MAC address before change active slave.
>>
>> Signed-off-by: Ding Tianhong <[email-masked]>
>> ---
>>  drivers/net/bonding/bond_main.c | 20 ++++++++++++++++++++
>>  1 file changed, 20 insertions(+)
>>
> 
> This doesn't seem to be true:
> ~# cat /sys/class/net/bond0/bonding/fail_over_mac 
> follow 2
> root@debian:~# ip l sh eth1
> 3: eth1: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT group default qlen 1000
>     link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
> root@debian:~# ip l sh eth2
> 4: eth2: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT group default qlen 1000
>     link/ether 52:54:00:4f:a5:99 brd ff:ff:ff:ff:ff:ff
> root@debian:~# ip l sh bond0
> 26: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default 
>     link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
> 
> *eth1 is the first and active slave and bond0 has taken its mac.
> Now trying your steps:
> Step 3) (bringing down the active eth1)
> root@debian:~# ip l set eth1 down
> root@debian:~# ip l sh bond0
> 26: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default 
>     link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
> root@debian:~# ip l sh eth1
> 3: eth1: <BROADCAST,MULTICAST,SLAVE> mtu 1500 qdisc pfifo_fast master bond0 state DOWN mode DEFAULT group default qlen 1000
>     link/ether 52:54:00:4f:a5:99 brd ff:ff:ff:ff:ff:ff
> root@debian:~# ip l sh eth2
> 4: eth2: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT group default qlen 1000
>     link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
> 
> *The mac addresses of eth1 and eth2 are correctly swapped, so far so good.
> 
> Step 4) (bringing down the active eth2)
> root@debian:~# ip l set eth2 down
> 3: eth1: <BROADCAST,MULTICAST,SLAVE> mtu 1500 qdisc pfifo_fast master bond0 state DOWN mode DEFAULT group default qlen 1000
>     link/ether 52:54:00:4f:a5:99 brd ff:ff:ff:ff:ff:ff
> 4: eth2: <BROADCAST,MULTICAST,SLAVE> mtu 1500 qdisc pfifo_fast master bond0 state DOWN mode DEFAULT group default qlen 1000
>     link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
> 26: bond0: <NO-CARRIER,BROADCAST,MULTICAST,MASTER,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default 
>     link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
> 
> *eth2 has kept the mac address of the bond and they're both down now
> 
> Step 5) (bring eth1 up again and observe the macs)
> ~# ip l set eth1 up
> 3: eth1: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT group default qlen 1000
>     link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
> 4: eth2: <BROADCAST,MULTICAST,SLAVE> mtu 1500 qdisc pfifo_fast master bond0 state DOWN mode DEFAULT group default qlen 1000
>     link/ether 52:54:00:4f:a5:99 brd ff:ff:ff:ff:ff:ff
> 26: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default 
>     link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
> 
> *The macs are correctly swapped and there's no such bug. 
> 
> Step 6(?) bring eth2 up
> ~# ip l set eth2 up
> 3: eth1: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT group default qlen 1000
>     link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
> 4: eth2: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT group default qlen 1000
>     link/ether 52:54:00:4f:a5:99 brd ff:ff:ff:ff:ff:ff
> 26: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default 
>     link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
> 
> *Still correct.
> 
> Also the mac address that gets set is dev_addr which is changed when
> the swapping is done, if you'd like to get the original mac address
> you should be using slave->perm_hwaddr.
> 

Hi Nik:

Which kernel version do you use, I test this on kernel 3.19.8 and 4.2-rc2, this problem exist on both version,
maybe I miss something?

Ding

> Cheers,
>  Nik
> .