From: Feyd <[EMAIL PROTECTED]>
Date: Mon, 11 Jul 2005 07:43:10 +0200
> can I assume that hard_start_xmit will always get skbs with hard_header_len
> reserved? I need two more bytes at the start of the packet and I'm getting
> spurious panics in skb_push.
Typically, no. ->hard_start_xmit() has a fully built packet, hardware
headers and all.
Protocols push the hardware header and copy it into the packet
long before you get called. For example, look at
net/ipv4/ip_output.c:ip_finish_output2(), it takes the cached
ARP response hardware header and copies it into the packet like
so:
read_lock_bh(&hh->hh_lock);
hh_alen = HH_DATA_ALIGN(hh->hh_len);
memcpy(skb->data - hh_alen, hh->hh_data, hh_alen);
read_unlock_bh(&hh->hh_lock);
skb_push(skb, hh->hh_len);
return hh->hh_output(skb);
Your driver's ->hard_start_xmit() gets the packet after this
has occured.
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