netdev - Re: [PATCH] net: clear iflink when moving to a new netns

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Date:	Wed, 12 Feb 2014 08:33:22 -0800
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Cong Wang <cwang@...pensource.com>
Subject: Re: [PATCH] net: clear iflink when moving to a new netns

On Tue, 11 Feb 2014 15:51:28 -0800
Cong Wang <xiyou.wangcong@...il.com> wrote:

> From: Cong Wang <cwang@...pensource.com>
> 
> BZ: https://bugzilla.kernel.org/show_bug.cgi?id=66691
> 
> macvlan and vlan both use iflink to identify its lower device,
> however, after such device is moved to the new netns, its iflink
> would become meaningless as ifindex is per netns. So, instead of
> forbid them moving to another netns, just clear this field so that
> it will not be dumped at least.
> 
> Cc: David S. Miller <davem@...emloft.net>
> Cc: Eric W. Biederman <ebiederm@...ssion.com>
> Cc: Eric Dumazet <eric.dumazet@...il.com>
> Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>,
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> Signed-off-by: Cong Wang <cwang@...pensource.com>
> ---
>  net/core/dev.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 4ad1b78..5e88b0c2 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -6608,12 +6608,11 @@ int dev_change_net_namespace(struct net_device *dev, struct net *net, const char
>  	dev_net_set(dev, net);
>  
>  	/* If there is an ifindex conflict assign a new one */
> -	if (__dev_get_by_index(net, dev->ifindex)) {
> -		int iflink = (dev->iflink == dev->ifindex);
> +	if (__dev_get_by_index(net, dev->ifindex))
>  		dev->ifindex = dev_new_index(net);
> -		if (iflink)
> -			dev->iflink = dev->ifindex;
> -	}
> +
> +	/* Old iflink is meaningless in the new namespace */
> +	dev->iflink = dev->ifindex;
>  
>  	/* Send a netdev-add uevent to the new namespace */
>  	kobject_uevent(&dev->dev.kobj, KOBJ_ADD);

This also breaks propogation of state changes from lower device
to upper device. Things like carrier and up/down.

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