netdev - Re: [PATCH net 2/2] net: bcmgenet: fix skb_len in bcmgenet_xmit

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Date:	Wed, 23 Mar 2016 14:24:37 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Petri Gynther <pgynther@...gle.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, f.fainelli@...il.com,
	jaedon.shin@...il.com, edumazet@...gle.com
Subject: Re: [PATCH net 2/2] net: bcmgenet: fix skb_len in
 bcmgenet_xmit_single()

On Wed, 2016-03-23 at 13:01 -0700, Petri Gynther wrote:
> skb_len needs to be skb_headlen(skb) in bcmgenet_xmit_single().
> 
> Fragmented skbs can have only Ethernet + IP + TCP headers (14+20+20=54 bytes)
> in the linear buffer, followed by the rest in fragments. Bumping skb_len to
> ETH_ZLEN would be incorrect for this case, as it would introduce garbage
> between TCP header and the fragment data.
> 
> This also works with regular/non-fragmented small packets < ETH_ZLEN bytes.
> Successfully tested this on GENETv3 with 42-byte ARP frames.
> 
> For testing, I used:
> ethtool -K eth0 tx-checksum-ipv4 off
> ethtool -K eth0 tx-checksum-ipv6 off
> echo 0 > /proc/sys/net/ipv4/tcp_timestamps
> 
> Signed-off-by: Petri Gynther <pgynther@...gle.com>
> ---
>  drivers/net/ethernet/broadcom/genet/bcmgenet.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> index 9990582..00da239 100644
> --- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> +++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> @@ -1298,7 +1298,7 @@ static int bcmgenet_xmit_single(struct net_device *dev,
>  
>  	tx_cb_ptr->skb = skb;
>  
> -	skb_len = skb_headlen(skb) < ETH_ZLEN ? ETH_ZLEN : skb_headlen(skb);
> +	skb_len = skb_headlen(skb);
>  
>  	mapping = dma_map_single(kdev, skb->data, skb_len, DMA_TO_DEVICE);
>  	ret = dma_mapping_error(kdev, mapping);

Acked-by: Eric Dumazet <edumazet@...gle.com>