netdev - Re: [PATCH] Virtual ethernet tunnel (v.2)

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Date:	Thu, 07 Jun 2007 08:23:09 -0700
From:	Ben Greear <greearb@...delatech.com>
To:	Pavel Emelianov <xemul@...nvz.org>
CC:	David Miller <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Patrick McHardy <kaber@...sh.net>,
	Daniel Lezcano <dlezcano@...ibm.com>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	Kirill Korotaev <dev@...nvz.org>,
	Linux Containers <containers@...ts.osdl.org>
Subject: Re: [PATCH] Virtual ethernet tunnel (v.2)

Pavel Emelianov wrote:
> Veth stands for Virtual ETHernet. It is a simple tunnel driver
> that works at the link layer and looks like a pair of ethernet
> devices interconnected with each other.
>   
As Dave mentioned, there is already a driver known as 'veth'.  Maybe borrow
the etun name as well?

I would also like some way to identify veth from other device types, 
preferably
something like a value in sysfs.   However, that should not hold up 
consideration of
this patch, and I am willing to submit a patch after this goes in to add 
the functionality
I want...

> +/*
> + * xmit
> + */
> +
> +static int veth_xmit(struct sk_buff *skb, struct net_device *dev)
> +{
> +	struct net_device *rcv = NULL;
> +	struct veth_device_stats *stats;
> +	struct veth_priv *priv, *rcv_priv;
> +	int length, cpu;
> +
> +	skb_orphan(skb);
> +
> +	priv = netdev_priv(dev);
> +	cpu = smp_processor_id();
> +	stats = per_cpu_ptr(priv->stats, cpu);
> +	rcv = priv->peer;
> +
> +	if (!(rcv->flags & IFF_UP))
> +		goto outf;
>   
I think you need at least the option to zero out the time-stamp, 
otherwise it will
not be re-calculated when received on the peer, and it potentially spent 
significant
time since it was last calculated (think netem delay or similar).

+        /* Zero out the time-stamp so that receiving code is forced
+         * to recalculate it.
+         */
+        skb->tstamp.off_sec = 0;
+        skb->tstamp.off_usec = 0;

> +
> +	rcv_priv = netdev_priv(rcv);
> +	skb->pkt_type = PACKET_HOST;
> +	skb->protocol = eth_type_trans(skb, rcv);
> +	if (dev->features & NETIF_F_NO_CSUM)
> +		skb->ip_summed = rcv_priv->ip_summed;
> +
> +	dst_release(skb->dst);
> +	skb->dst = NULL;
> +	secpath_reset(skb);
> +	nf_reset(skb);
> +	skb->mark = 0;
> +
> +	length = skb->len;
>   
This should be done before you do the eth_type_trans, as that pulls the 
header and your
byte counters will be off.

> +
> +	stats->tx_bytes += length;
> +	stats->tx_packets++;
>   
> +
> +	stats = per_cpu_ptr(rcv_priv->stats, cpu);
> +	stats->rx_bytes += length;
> +	stats->rx_packets++;
> +
> +	netif_rx(skb);
> +	return 0;
> +
> +outf:
> +	kfree_skb(skb);
> +	stats->tx_dropped++;
> +	return 0;
> +}
>   
Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com> 
Candela Technologies Inc  http://www.candelatech.com


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