netdev - Re: [net] net_sched: make dev_trans_start return vlan's real dev trans

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Date:	Sat, 3 Aug 2013 20:25:01 +0200
From:	Veaceslav Falico <vfalico@...hat.com>
To:	Nikolay Aleksandrov <nikolay@...hat.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, fubar@...ibm.com,
	jhs@...atatu.com
Subject: Re: [net] net_sched: make dev_trans_start return vlan's real dev
 trans_start

On Sat, Aug 03, 2013 at 08:19:10PM +0200, Nikolay Aleksandrov wrote:
>On 08/03/2013 08:13 PM, Nikolay Aleksandrov wrote:
>> On 08/03/2013 07:07 PM, Veaceslav Falico wrote:
>>> On Sat, Aug 03, 2013 at 05:07:51PM +0200, nikolay@...hat.com wrote:
>>> ...snip...
>>>> +    while (is_vlan_dev(dev))
>>>> +        dev = vlan_dev_real_dev(dev);
>>>
>>> While at it - I've checked a few users (mainly network drivers) of
>>> vlan_dev_real_dev(dev) and they all rely on that the return device would be
>>> the *real* device, but not another vlan.
>>>
>>> So maybe we should move this while loop to vlan_dev_real_dev() instead?
><snip>
>> Not really, there're users that rely to get only 1 level of real_dev (e.g.
>> netxen ip config which expects a configuration like vlan -> bond -> netxen,
>> and it needs to go from vlan to bond only) which will be broken, there're
>Scratch this part, I need to get some sleep :-)

:)

Yeah, it only modifies the QinQ scenario. I've never used it personally,
though.

Here you go, I think the code is more readable than my english:

diff --git a/net/8021q/vlan_core.c b/net/8021q/vlan_core.c
index 4a78c4d..6ee48aa 100644
--- a/net/8021q/vlan_core.c
+++ b/net/8021q/vlan_core.c
@@ -91,7 +91,12 @@ EXPORT_SYMBOL(__vlan_find_dev_deep);
  
  struct net_device *vlan_dev_real_dev(const struct net_device *dev)
  {
-	return vlan_dev_priv(dev)->real_dev;
+	struct net_device *ret = vlan_dev_priv(dev)->real_dev;
+
+	while (is_vlan_dev(ret))
+		ret = vlan_dev_priv(ret)->real_dev;
+
+	return ret;
  }
  EXPORT_SYMBOL(vlan_dev_real_dev);
  

>
>
>> also many non-ethernet users which may rely on similar behaviour.
>> Most of the network drivers don't expect a *real* device, they check if the
>> returned device is one of their own after using that function.

True, and in case of vlan -> vlan -> dev they'll won't find themselves,
which is bad.

>> I'd suggest using a helper that uses vlan_dev_real_dev so we will have both
>> without breaking anything.

I don't have any preference in that, tbh, I don't know the vlan part that
good :).

>>
>> Nik
>> --
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>
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