Subject: Re: [PATCH] net: Handle gso packets in dev_forward_skb

From: Daniel Lezcano <[email-masked]>
Date: Tue, 29 Mar 2011 14:54:43 +0200

On 03/28/2011 09:20 PM, Eric Dumazet wrote:
> Le dimanche 27 mars 2011 à 18:09 -0700, David Miller a écrit :
>> From: [email-masked] (Eric W. Biederman)
>> Date: Mon, 21 Mar 2011 15:00:56 -0700
>>
>>> Eric Dumazet<[email-masked]>  writes:
>>>
>>>> Hmm, did you follow http://patchwork.ozlabs.org/patch/86815/
>>>> discussion ?
>>> No.  It seems I missed it, but I do have the same problem, and
>>> essentially the same fix.
>> Can someone work on getting this straightened out and resubmit the
>> final patch so I can apply something?
>>
> Apparently Daniel is busy.

Yes, sorry for the delay.
I would like to fix it but I am not sure to understand the different 
solutions proposed.

On 03/28/2011 09:20 PM, Eric Dumazet wrote:
> Le dimanche 27 mars 2011 à 18:09 -0700, David Miller a écrit :
>> From: [email-masked] (Eric W. Biederman)
>> Date: Mon, 21 Mar 2011 15:00:56 -0700
>>
>>> Eric Dumazet<[email-masked]>  writes:
>>>
>>>> Hmm, did you follow http://patchwork.ozlabs.org/patch/86815/
>>>> discussion ?
>>> No.  It seems I missed it, but I do have the same problem, and
>>> essentially the same fix.
>> Can someone work on getting this straightened out and resubmit the
>> final patch so I can apply something?
>>
> Apparently Daniel is busy.

Yes, sorry for the delay.
I would like to fix it, but my knowledge in limited on offloading.

I did the following patch, it fixes the problem. If it looks good I can 
resend it in patch format:

Index: net-2.6/net/core/dev.c
===================================================================
--- net-2.6.orig/net/core/dev.c 2011-03-29 14:50:00.047646000 +0200
+++ net-2.6/net/core/dev.c      2011-03-29 14:50:35.587646000 +0200
@@ -1454,6 +1454,27 @@ static inline void net_timestamp_check(s
                 __net_timestamp(skb);
  }

+static inline bool is_skb_forwardable(struct net_device *dev,
+                                     struct sk_buff *skb)
+{
+       unsigned int len;
+
+       if (!(dev->flags & IFF_UP))
+               return false;
+
+       len = dev->mtu + dev->hard_header_len + VLAN_HLEN;
+       if (skb->len <= len)
+               return true;
+
+       /* if TSO is enabled, we don't care about the length as the packet
+        * could be forwarded without being segmented before
+        */
+       if (skb_is_gso(skb))
+               return true;
+
+       return false;
+}
+
  /**
   * dev_forward_skb - loopback an skb to another netif
   *
@@ -1477,8 +1498,7 @@ int dev_forward_skb(struct net_device *d
         skb_orphan(skb);
         nf_reset(skb);

-       if (unlikely(!(dev->flags & IFF_UP) ||
-                    (skb->len > (dev->mtu + dev->hard_header_len + 
VLAN_HLEN)))) {
+       if (unlikely(!is_skb_forwardable(dev, skb))) {
                 atomic_long_inc(&dev->rx_dropped);
                 kfree_skb(skb);
                 return NET_RX_DROP;