netdev - Re: GSO and IPv4 forwarding

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Message-ID: <1288124114.2652.25.camel@edumazet-laptop>
Date:	Tue, 26 Oct 2010 22:15:14 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Kevin Wilson <wkevils@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: GSO and IPv4 forwarding

Le mardi 26 octobre 2010 à 22:02 +0200, Kevin Wilson a écrit :
> Hi,
> When we set a netdevice to support forwarding, we disable LRO.
> This is done because we don't want to forward an SKB which has been
> processed by LRO.
> 
> This is done in inet_forward_change() in net/ipv4/devinet.c:
> We call dev_disable_lro(dev) in this method, when setting forwarding
> for the device.
> As a result, in ip_forward(), the packet will be dropped. (because
> skb_warn_if_lro(), called by this method,  returns TRUE)
> 
> My question is:
> dev_disable_lro(dev) disable the LRO feature (NETIF_F_LRO) of the
> device. But suppose I have a device where GRO is enabled (and LRO is
> not). And let's say I set forwarding on this device.
> 
> it seems to me that is such case, calling dev_disable_lro(dev)  in
> net_forward_change() to disable the LRO feature of the device (which
> is already disabled) is not enough, and in such case , GRO packets,
> which want to be forwarded,  will **not** be dropped in ip_forward().
> (since kb_warn_if_lro() will return false in this case)
> 
> Is it so ? I am ready to send a patch fixing it, but I am a newbie in
> kernel, so I want to ask first.

GRO packets can be forwarded just fine.



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