linux-kernel - Re: [PATCH ref0] net: add Faraday FTMAC100 10/100 Ethernet driver

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Date:	Thu, 24 Feb 2011 18:48:05 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Po-Yu Chuang <ratbert.chuang@...il.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	bhutchings@...arflare.com, joe@...ches.com, dilinger@...ued.net,
	mirqus@...il.com, davem@...emloft.net,
	Po-Yu Chuang <ratbert@...aday-tech.com>
Subject: Re: [PATCH ref0] net: add Faraday FTMAC100 10/100 Ethernet driver

Le jeudi 24 février 2011 à 18:39 +0100, Eric Dumazet a écrit :
> Le jeudi 24 février 2011 à 17:29 +0800, Po-Yu Chuang a écrit :
> > From: Po-Yu Chuang <ratbert@...aday-tech.com>
> > 
> 
> 
> > +
> > +static bool ftmac100_rx_packet(struct ftmac100 *priv, int *processed)
> > +{
> > +	struct net_device *netdev = priv->netdev;
> > +	struct ftmac100_rxdes *rxdes;
> > +	struct sk_buff *skb;
> > +	struct page *page;
> > +	dma_addr_t map;
> > +	int length;
> > +
> > +	rxdes = ftmac100_rx_locate_first_segment(priv);
> > +	if (!rxdes)
> > +		return false;
> > +
> > +	if (unlikely(ftmac100_rx_packet_error(priv, rxdes))) {
> > +		ftmac100_rx_drop_packet(priv);
> > +		return true;
> > +	}
> > +
> > +	/*
> > +	 * It is impossible to get multi-segment packets
> > +	 * because we always provide big enough receive buffers.
> > +	 */
> > +	if (unlikely(!ftmac100_rxdes_last_segment(rxdes)))
> > +		BUG();
> > +
> > +	/* start processing */
> > +	skb = netdev_alloc_skb_ip_align(netdev, ETH_HLEN);
> 
> Oh I see... You should allocate a bigger head (say... 128 bytes)
> 
> And copy in it up to 128 bytes of first part... this to avoid upper
> stack to reallocate skb head (because IP/TCP processing need to get
> their headers in skb head)

Take a look at drivers/net/niu.c :

#define RX_SKB_ALLOC_SIZE   128 + NET_IP_ALIGN

static int niu_process_rx_pkt(...)
{
	...
	skb = netdev_alloc_skb(np->dev, RX_SKB_ALLOC_SIZE);
	...
	while (1) {
	 	...
		niu_rx_skb_append(skb, page, off, append_size);
	}
}



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