Re: [PATCH] gianfar: reallocate skb when headroom is not enough for fcb

[David Miller <davem@davemloft.net>]

From: Stephen Hemminger <shemminger@vyatta.com>
Date: Wed, 25 Mar 2009 08:53:33 -0700

> Overall, this looks like the wrong code (not copying back new skb)
> and in awkward place. Also your version doesn't handle case where
> skb headroom is not writable.

headroom is always writable and usable by the driver, this
is the exact same code sequence we use in drivers/net/niu.c
for this purpose:

	len = sizeof(struct tx_pkt_hdr) + 15;
	if (skb_headroom(skb) < len) {
		struct sk_buff *skb_new;

		skb_new = skb_realloc_headroom(skb, len);
		if (!skb_new) {
			rp->tx_errors++;
			goto out_drop;
		}
		kfree_skb(skb);
		skb = skb_new;

otherwise the code we just came from wouldn't be able
to push even the ethernet header there.