netdev - Re: [PATCH net-next 2/3] udp: move logic out of udp[46]_ufo_send

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Date:	Sat, 20 Sep 2014 18:12:34 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/3] udp: move logic out of
 udp[46]_ufo_send_check

On Sat, 2014-09-20 at 14:52 -0700, Tom Herbert wrote:
> In udp[46]_ufo_send_check the UDP checksum initialized to the pseudo
> header checksum. We can move this logic into udp[46]_ufo_fragment.
> After this change udp[64]_ufo_send_check is a no-op.
> 
> Signed-off-by: Tom Herbert <therbert@...gle.com>
> ---
>  net/ipv4/udp_offload.c | 37 +++++++++++++++----------------------
>  net/ipv6/udp_offload.c | 40 ++++++++++++++++++----------------------
>  2 files changed, 33 insertions(+), 44 deletions(-)
> 
> diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
> index d7c43f7..2918cc9 100644
> --- a/net/ipv4/udp_offload.c
> +++ b/net/ipv4/udp_offload.c
> @@ -27,23 +27,6 @@ struct udp_offload_priv {
>  
>  static int udp4_ufo_send_check(struct sk_buff *skb)
>  {
> -	if (!pskb_may_pull(skb, sizeof(struct udphdr)))
> -		return -EINVAL;
> -
> -	if (likely(!skb->encapsulation)) {
> -		const struct iphdr *iph;
> -		struct udphdr *uh;
> -
> -		iph = ip_hdr(skb);
> -		uh = udp_hdr(skb);
> -
> -		uh->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr, skb->len,
> -				IPPROTO_UDP, 0);
> -		skb->csum_start = skb_transport_header(skb) - skb->head;
> -		skb->csum_offset = offsetof(struct udphdr, check);
> -		skb->ip_summed = CHECKSUM_PARTIAL;
> -	}
> -
>  	return 0;
>  }
>  
> @@ -128,8 +111,9 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
>  {
>  	struct sk_buff *segs = ERR_PTR(-EINVAL);
>  	unsigned int mss;
> -	int offset;
>  	__wsum csum;
> +	struct udphdr *uh;
> +	struct iphdr *iph;
>  
>  	if (skb->encapsulation &&
>  	    (skb_shinfo(skb)->gso_type &
> @@ -138,6 +122,9 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
>  		goto out;
>  	}
>  
> +	if (!pskb_may_pull(skb, sizeof(struct udphdr)))
> +		goto out;
> +
>  	mss = skb_shinfo(skb)->gso_size;
>  	if (unlikely(skb->len <= mss))
>  		goto out;
> @@ -165,10 +152,16 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
>  	 * HW cannot do checksum of UDP packets sent as multiple
>  	 * IP fragments.
>  	 */
> -	offset = skb_checksum_start_offset(skb);
> -	csum = skb_checksum(skb, offset, skb->len - offset, 0);
> -	offset += skb->csum_offset;
> -	*(__sum16 *)(skb->data + offset) = csum_fold(csum);
> +
> +	uh = udp_hdr(skb);
> +	iph = ip_hdr(skb);
> +
> +	uh->check = 0;
> +	csum = skb_checksum(skb, 0, skb->len, 0);
> +	uh->check = udp_v4_check(skb->len, iph->saddr, iph->daddr, csum);
> +	if (uh->check == 0)
> +		uh->check = CSUM_MANGLED_0;
> +
>  	skb->ip_summed = CHECKSUM_NONE;


Shouldn't it be changed to CHECKSUM_PARTIAL or something ?

udp4_ufo_send_check() was able to fill CHECKSUM_PARTIAL,
I fear I do not understand enough this part.





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