netdev - Re: [PATCH] vxlan: Accept user specified MTU value when create new vxlan link

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Date:	Sat, 28 May 2016 23:22:28 +0800
From:	oc <oc@...ify.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH] vxlan: Accept user specified MTU value when create new
 vxlan link

On 2016/05/28 00:09, Cong Wang wrote:
> On Thu, May 26, 2016 at 7:49 PM, Chen Haiquan <oc@...ify.com> wrote:
>> When create a new vxlan link, example:
>>    ip link add vtap mtu 1440 type vxlan vni 1 dev eth0
>>
>> The argument "mtu" has no effect, because it is not set to conf->mtu. The
>> default value is used in vxlan_dev_configure function.
>>
>> This problem was introduced by commit 0dfbdf4102b9 (vxlan: Factor out device
>> configuration).
>>
>> Fixes: 0dfbdf4102b9 (vxlan: Factor out device configuration)
>>
>> Signed-off-by:  Chen Haiquan <oc@...ify.com>
>> ---
>>   drivers/net/vxlan.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
>> index 8ff30c3..f999db2 100644
>> --- a/drivers/net/vxlan.c
>> +++ b/drivers/net/vxlan.c
>> @@ -3086,6 +3086,9 @@ static int vxlan_newlink(struct net *src_net, struct net_device *dev,
>>          if (data[IFLA_VXLAN_REMCSUM_NOPARTIAL])
>>                  conf.flags |= VXLAN_F_REMCSUM_NOPARTIAL;
>>
>> +       if (tb[IFLA_MTU])
>> +               conf.mtu = nla_get_u32(tb[IFLA_MTU]);
>> +
> IFLA_MTU is already parsed in rtnl_create_link(),
> so just use dev->mtu here? conf.mtu = dev->mtu?
Two reasons:
1. vxlan_dev_configure function check conf->mtu to determine if it need 
to change value of dev->mtu.
The logical looks better to get conf->mtu from IFLA_MTU directly.
2. This problem is a regression. The old code check tb[IFLA_MTU]. I want 
to use the same way as the past.