netdev - Re: data is truncated in skb

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Date:	Fri, 2 Mar 2012 16:25:25 +0500
From:	Syed Muhammad Mohsin Kazmi <08beesmmkazmi@...cs.edu.pk>
To:	Stephen Hemminger <shemminger@...tta.com>, netdev@...r.kernel.org
Subject: Re: data is truncated in skb

here is the code of encapsulation...!

struct sk_buff *create_trill_header(struct sk_buff *skb,bool
trill_header_ok,size_t msglen)
{

	unsigned int extra_header_length;
	uint16_t ether_type;
	struct trill_header *push1;
	struct ethhdr *push2;
	struct ethhdr *push3;

	ether_type = msglen > 0 ? (uint16_t)msglen : ETHERTYPE_TRILL;

	extra_header_length = trill_header_ok ? 0 : sizeof (struct trill_header);

	struct ethhdr *mac_header = eth_hdr(skb);

	if (mac_header == NULL)
	{
		// error handling
		printk("mac_header Error\n");
	}
	
	printk("\t\t\tOriginal Buffer\n");
	
	trill_testing(skb);

	if ( skb_headroom(skb) < 2*sizeof(struct ethhdr ) + sizeof(struct
trill_header) )
	{
		skb = skb_realloc_headroom(skb,34);
		printk("\t\t\tHEADROOM ALLOCATION\n");
	}
	
	push2 = (struct ethhdr *)skb_push(skb,ETH_HLEN);
	
	memcpy(push2->h_dest,mac_header->h_dest,ETH_ALEN);
	
	memcpy(push2->h_source,mac_header->h_source,ETH_ALEN);
	
	push2->h_proto = htons(0x0800); // ether_type IP
	
	push1 = (struct trill_header *)skb_push(skb,extra_header_length);
	
	push1->th_version =  TRILL_PROTOCOL_VERSION;
	
	push1->th_reserved = TRILL_RESERVED_BITS;
	
	push1->th_multidest =  TRILL_UNICAST;
	
	push1->th_optslen_hi = 0;

	push1->th_optslen_lo = 0;
	
	push1->th_hopcount = DEFAULT_HOPCOUNT;
	
	push1->th_egressnick = htons(0x1600);
	
	push1->th_ingressnick = htons(0x1500);
	
	push3 = (struct ethhdr *)skb_push(skb,ETH_HLEN);
	
	memcpy(push3->h_dest,mac_header->h_dest,ETH_ALEN);
	
	memcpy(push3->h_source,mac_header->h_source,ETH_ALEN);
	
	push3->h_proto = htons(ether_type); // ether_type Trill
	
	if(skb->data == push3)
	{
		skb_set_mac_header(skb,0);
	
		skb_pull(skb,ETH_HLEN);
	
		mac_header = eth_hdr(skb);
	
	}
	
	printk("\t\t\tencapsulated Buffer\n");
	
	trill_testing(skb);
	
	return skb;
	
}

On Fri, Mar 2, 2012 at 9:07 AM, Stephen Hemminger <shemminger@...tta.com> wrote:
> On Fri, 2 Mar 2012 07:17:16 +0500
> Syed Muhammad Mohsin Kazmi <08beesmmkazmi@...cs.edu.pk> wrote:
>
>> hi,
>>   I have written a code which encapsulates the packets GOINGOUT or
>> OTHERHOST in bridging module. Encapsulation is done fine. But data at
>> the end of buffer is truncated by the size of encapsulation. What
>> should i do to avoid truncation of data?
>
>
> No idea. Post question and code to netdev list
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