netdev - Re: [net-next 1/5] macvtap: set transport header before passing skb to lower device

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Date:	Tue, 26 Mar 2013 08:06:47 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, mst@...hat.com,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [net-next 1/5] macvtap: set transport header before passing skb
 to lower device

On Tue, 2013-03-26 at 14:19 +0800, Jason Wang wrote:
> Set the transport header for 1) some drivers (e.g ixgbe) needs l4 header 2)
> precise packet length estimation (introduced in 1def9238) needs l4 header to
> compute header length.
> 
> For the packets with partial checksum, the patch just set the transport header
> to csum_start. Otherwise tries to use skb_flow_dissect() to get l4 offset, if it
> fails, just pretend no l4 header.
> 
> Cc: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/net/macvtap.c |    9 +++++++++
>  1 files changed, 9 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index a449439..acf6450 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -21,6 +21,7 @@
>  #include <net/rtnetlink.h>
>  #include <net/sock.h>
>  #include <linux/virtio_net.h>
> +#include <net/flow_keys.h>
>  
>  /*
>   * A macvtap queue is the central object of this driver, it connects
> @@ -645,6 +646,7 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
>  	int vnet_hdr_len = 0;
>  	int copylen = 0;
>  	bool zerocopy = false;
> +	struct flow_keys keys;
>  
>  	if (q->flags & IFF_VNET_HDR) {
>  		vnet_hdr_len = q->vnet_hdr_sz;
> @@ -725,6 +727,13 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
>  			goto err_kfree;
>  	}
>  
> +	if (skb->ip_summed == CHECKSUM_PARTIAL)

where ip_summed is set to this value ?

> +		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_set_transport_header(skb, ETH_HLEN);
> +
>  	rcu_read_lock_bh();
>  	vlan = rcu_dereference_bh(q->vlan);
>  	/* copy skb_ubuf_info for callback when skb has no error */

This driver has nice helpers.

You should add this code in a helper as well.

Because its not clear at this point if csum_start/csum_offset/ip_summed
are consistent.



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