Re: [PATCH] net: skb_set_dev do not unconditionally drop ref to dst

[Eric Dumazet <eric.dumazet@gmail.com>]

On Mon, 2012-04-30 at 07:38 +0200, Frank Blaschka wrote:
> From: Frank Blaschka <frank.blaschka@de.ibm.com>
> 
> commit 8a83a00b0735190384a348156837918271034144 unconditionally
> drops dst reference when skb->dev is set. This causes a regression
> with VLAN and the qeth_l3 network driver. qeth_l3 can not get gw
> information from the skb coming from the vlan driver. It is only
> valid to drop the dst in case of different name spaces.
> 
> Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
> ---
>  net/core/dev.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1881,8 +1881,8 @@ EXPORT_SYMBOL(netif_device_attach);
>  #ifdef CONFIG_NET_NS
>  void skb_set_dev(struct sk_buff *skb, struct net_device *dev)
>  {
> -	skb_dst_drop(skb);
>  	if (skb->dev && !net_eq(dev_net(skb->dev), dev_net(dev))) {
> +		skb_dst_drop(skb);
>  		secpath_reset(skb);
>  		nf_reset(skb);
>  		skb_init_secmark(skb);
> 

You forgot CC Arnd Bergmann <arnd@arndb.de> ?

But we do want to do the skb_dst_drop() in dev_forward_skb()

Your patch breaks dev_forward_skb() then.

But apparently this forward path was alredy broken in Arnd patch...