Re: [net-next 2/5] tuntap: set transport header before passing it to kernel

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

On Tue, 2013-03-26 at 14:19 +0800, Jason Wang wrote:
> Currently, for the packets receives from tuntap, before doing header check,
> kernel just reset the transport header in netif_receive_skb() which pretends no
> l4 header. This is suboptimal for precise packet length estimation (introduced
> in 1def9238) which needs correct l4 header for gso packets.
> 
> So this patch set the transport header to csum_start for partial checksum
> packets, otherwise it first try skb_flow_dissect(), if it fails, just reset the
> transport header.
> 
> Cc: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  drivers/net/tun.c |   10 ++++++++++
>  1 files changed, 10 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 95837c1..48cd73a 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -70,6 +70,7 @@
>  #include <net/sock.h>
>  
>  #include <asm/uaccess.h>
> +#include <net/flow_keys.h>
>  
>  /* Uncomment to enable debugging */
>  /* #define TUN_DEBUG 1 */
> @@ -1049,6 +1050,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
>  	bool zerocopy = false;
>  	int err;
>  	u32 rxhash;
> +	struct flow_keys keys;
>  
>  	if (!(tun->flags & TUN_NO_PI)) {
>  		if ((len -= sizeof(pi)) > total_len)
> @@ -1203,6 +1205,14 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
>  	}
>  
>  	skb_reset_network_header(skb);
> +
> +	if (skb->ip_summed == CHECKSUM_PARTIAL)
> +		skb_set_transport_header(skb, skb_checksum_start_offset(skb));
> +	else if (skb_flow_dissect(skb, &keys))
> +		skb_set_transport_header(skb, keys.thoff);
> +	else
> +		skb_reset_transport_header(skb);
> +
>  	rxhash = skb_get_rxhash(skb);
>  	netif_rx_ni(skb);
>  

Another call for a common helper.