Subject: Re: [PATCH] bonding: Allow tun-interfaces as slaves

From: Ding Tianhong <[email-masked]>
Date: Tue, 30 Aug 2016 09:44:36 +0800

On 2016/8/12 2:24, Jörn Engel wrote:
> On Wed, Aug 10, 2016 at 05:58:38PM -0700, Jay Vosburgh wrote:
>> Jörn Engel <[email-masked]> wrote:
>>> On Wed, Aug 10, 2016 at 02:26:49PM -0700, Jörn Engel wrote:
>>>>
>>>> Having to set one more parameter is a bit annoying.  It would have to be
>>>> documented in a prominent place and people would still often miss it.
>>>> So I wonder if we can make the interface a little nicer.
>>>>
>>>> Options:
>>>> - If there are no slaves yet and the first slave added is tun, we trust
>>>>   the users to know what they are doing.  Automatically set
>>>>   bond->params.fail_over_mac = BOND_FOM_KEEPMAC
>>>>   Maybe do a printk to inform the user in case of a mistake.
>>
>> 	I don't think this is feasible, as I don't see a reliable way to
>> test for a slave being a tun device (ARPHRD_NONE is not just tun, and we
>> cannot check the ops as they are not statically built into the kernel).
>> I'm also not sure that heuristics are the proper way to enable this
>> functionality in general.
> 
> I was looking for a slightly more generic thing than "is this device
> tun?".  Something along the lines of "is this device L3 only?".  We can
> always introduce a new flag and have tun set the flag.  Naïve me thought
> ARPHRD_NONE might already match what I was looking for.
> 

I think there is no such flag to distinguish the tun device, if you insistent on to support new flag
for Tun device, you could send a patch and we could review it, otherwise BOND_FOM_KEEPMAC is enough to
fix this problem.

Thanks
Ding

> But if such an approach causes problems for others, it is a non-starter.
> 
>>>> - If we get an error and the slave device is tun, do a printk giving the
>>>>   user enough information to find this parameter.
>>
>> 	This could probably be done as a change the existing logic, e.g.,
>>
>> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>> index 1f276fa30ba6..019c1a689aae 100644
>> --- a/drivers/net/bonding/bond_main.c
>> +++ b/drivers/net/bonding/bond_main.c
>> @@ -1443,6 +1443,9 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
>>  				res = -EOPNOTSUPP;
>>  				goto err_undo_flags;
>>  			}
>> +		} else if (BOND_MODE(bond) != BOND_MODE_ACTIVEBACKUP &&
>> +			   bond->params.fail_over_mac != BOND_FOM_KEEPMAC) {
>> +				netdev_err(bond_dev, "The slave device specified does not support setting the MAC address, but fail_over_mac is not set to keepmac\n");
>>  		}
>>  	}
>>  
>> 	I haven't tested this, and I'm not sure it will get all corner
>> cases correct, but this should basically cover it.
> 
> Nit: Indentation is wrong (two tabs instead of one).
> 
> It should provide enough information for anyone that reads kernel messages.
> Works for me.
> 
> [588380.721349] bond1: Adding slave tun0
> [588380.721402] bond1: The slave device specified does not support setting the MAC address
> [588380.721404] bond1: The slave device specified does not support setting the MAC address, but fail_over_mac is not set to keepmac
> 
> Jörn
> 
> --
> It is easier to lead men to combat, stirring up their passion, than to
> restrain them and direct them toward the patient labours of peace.
> -- Andre Gide
> 
> .
>