The function is called like this- dev->hard_header(skb, dev, ptype,
dest_hw, src_hw, skb->len); where "skb->protocol" is same as "ptype",
but the former is expected to be in network byte order before calling
hard_header, while latter in host byte order (eth_header internally
does its own conversion of ptype). Is this deliberate? or a bug?
We've a driver, which sends pkt over ethernet. Here's the sample send routine-
my_eth_send(struct sk_buff * mp, struct net_device *dev, int linkno)
{
<snip>
mp->protocol = link->ln_sap;
mp->nh.raw = mp->data;
dev->hard_header(mp, mp->dev, ntohs(link->ln_sap),
dest_node->n_linkinfo[linkno].n_addr,
src_node->n_linkinfo[linkno].n_addr,
mp->len);
dev_queue_xmit(mp);
}
We store the type field (i.e., link->ln_sap) in our driver in network
byte order only (as skb->protocol is expected to be in network byte
order), but as eth_header internally does the conversion again, we've
to un-convert it (for every outgoing pkt!!) unnecessarily. We can get
away with this by using two different variables for ptype- one in n/w
order, other in host order; but unless there's some hidden magic
behind the current behavior, I'd like to send a patch to fix this in
kernel. Or if you think it would touch too many files, might break too
many things...we can let it be.
Regards,
-Kalash
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