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

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Message-Id: <20090325.144959.02893509.davem@davemloft.net>
Date:	Wed, 25 Mar 2009 14:49:59 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	shemminger@...tta.com
Cc:	leoli@...escale.com, netdev@...r.kernel.org
Subject: Re: [PATCH] gianfar: reallocate skb when headroom is not enough
 for fcb

From: Stephen Hemminger <shemminger@...tta.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.
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