Re: Pushing a stray sk_buff to the NIC

[Rui Sousa]

On Thu, 9 Jan 2003, Joshua Stewart wrote:

Hi,

> I'm trying to take "hand-built" sk_buffs with little more than some data
> and a dev member and push them to the NIC for transmission.  I would
> like to simply give them to dev_queue_xmit.  Does anybody know what
> state I should have them in before handing them to dev_queue_xmit? 

In a driver I wrote I setup (for a newly allocated skb and a 2.4 kernel):

	some_header = (struct some_header *) skb_push(skb, sizeof(struct some_header));

	skb->nh.raw = (unsigned char *) some_header;

	this_eth_hdr = (struct ethhdr *) skb_push(skb, ETH_HLEN);

	this_eth_hdr->h_proto = __constant_htons(ETH_P_SOME_HEADER);
	memcpy(this_eth_hdr->h_source, dev->dev_addr, ETH_ALEN);

	skb->dev = dev;
        skb->protocol = __constant_htons(ETH_P_CSM_ENCAPS);

	dev_queue_xmit(skb);

where some_header for you is probably an IP header and dev is the "struct 
net_device" of the device you are using to send the packet out on the 
wire.

> Should skb->data point to the start of a MAC header or an IP header?

MAC
 
> Also, given an IP address in skb->nh.iph->daddr, what's the easiest way
> to get the appropriate MAC address?

First you need to get the device, then the MAC address is easy. This 
should be what normal IP routing code does...

> J
> 
> 

Rui

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