netdev - Re: [PATCH v2] net: add Faraday FTMAC100 10/100 Ethernet driver

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Date:	Mon, 17 Jan 2011 18:58:38 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Po-Yu Chuang <ratbert.chuang@...il.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, ratbert@...aday-tech.com,
	joe@...ches.com, dilinger@...ued.net
Subject: Re: [PATCH v2] net: add Faraday FTMAC100 10/100 Ethernet driver

On Mon, 2011-01-17 at 18:29 +0100, Eric Dumazet wrote:
> Le lundi 17 janvier 2011 à 17:21 +0800, Po-Yu Chuang a écrit :
> 
> 
> > +static int ftmac100_rx_packet(struct ftmac100 *priv, int *processed)
> > +{
> > +	struct net_device *netdev = priv->netdev;
> > +	struct ftmac100_rxdes *rxdes;
> > +	struct sk_buff *skb;
> > +	int length;
> > +	int copied = 0;
> > +	int done = 0;
> > +
> > +	rxdes = ftmac100_rx_locate_first_segment(priv);
> > +	if (!rxdes)
> > +		return 0;
> > +
> > +	length = ftmac100_rxdes_frame_length(rxdes);
> > +
> > +	netdev->stats.rx_packets++;
> > +	netdev->stats.rx_bytes += length;
> > +
> > +	if (unlikely(ftmac100_rx_packet_error(priv, rxdes))) {
> > +		ftmac100_rx_drop_packet(priv);
> > +		return 1;
> > +	}
> > +
> > +	/* start processing */
> > +	skb = netdev_alloc_skb_ip_align(netdev, length);
> > +	if (unlikely(!skb)) {
> > +		if (net_ratelimit())
> > +			netdev_err(netdev, "rx skb alloc failed\n");
> > +
> > +		ftmac100_rx_drop_packet(priv);
> > +		return 1;
> > +	}
> > +
> 
> Please dont increase rx_packets/rx_bytes before the
> netdev_alloc_skb_ip_align().
> 
> In case of mem allocation failure, it would be better not pretending we
> handled a packet.
>
> drivers/net/r8169.c for example does the rx_packets/rx_bytes only if
> packet is delivered to upper stack.

That's news to me.  I specifically advised Po-Yu Chuang to increment
these earlier because my understanding is that all packets/bytes should
be counted.  And drivers which use hardware MAC stats will generally do
that, so I really don't think it makes sense to make other drivers
different deliberately.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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