Subject: Re: [PATCH] net: packet: option to only pass skb protocol

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 6 Jan 2010 11:12:57 +0200

On Tue, Jan 05, 2010 at 03:51:50PM -0800, David Miller wrote:
> From: "Chris Friesen" <[email-masked]>
> Date: Tue, 05 Jan 2010 16:13:29 -0600
> 
> > If SOCK_RAW packets are being sent, the protocol number is embedded in
> > the packet data
> 
> Where exactly is that protocol value?  Not every link level protocol
> is ethernet.
> 
> We support FDDI, HIPPI, wireless, VLAN, PPP, and a host of others.
> 
> So you can't know for sure unless you assume ethernet, which you
> can't do.

You are right.  This is TX though so the socket is bound to a specific
device, and devices know which link protocol they use.  So we could add a
get_protocol operation to each device type, and call it if the protocol
passed is ETH_P_ALL to get the real one.

Like this: except I only added this for ethernet, and I would have to
add this for the rest of device types. But I would like to hear what
others think about this before I do the rest of the work for the rest of
device types.

Does the below look sane?

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index a3fccc8..99d7801 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -319,6 +319,7 @@ struct header_ops {
 	void	(*cache_update)(struct hh_cache *hh,
 				const struct net_device *dev,
 				const unsigned char *haddr);
+	__be16	(*get_protocol)(struct sk_buff *skb, struct net_device *dev)
 };
 
 /* These flag bits are private to the generic network queueing
diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index 205a1c1..3e7761d 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -231,6 +231,17 @@ int eth_header_parse(const struct sk_buff *skb, unsigned char *haddr)
 EXPORT_SYMBOL(eth_header_parse);
 
 /**
+ * eth_get_protocol - extract protocol value from packet
+ * @skb: packet to extract protocol from
+ * @dev: source device
+ */
+__be16 eth_get_protocol(const struct sk_buff *skb, struct net_device *dev)
+{
+	const struct ethhdr *eth = eth_hdr(skb);
+	return eth->h_proto
+}
+
+/**
  * eth_header_cache - fill cache entry from neighbour
  * @neigh: source neighbour
  * @hh: destination cache entry
@@ -324,6 +335,7 @@ EXPORT_SYMBOL(eth_validate_addr);
 const struct header_ops eth_header_ops ____cacheline_aligned = {
 	.create		= eth_header,
 	.parse		= eth_header_parse,
+	.get_protocol   = eth_get_protocol,
 	.rebuild	= eth_rebuild_header,
 	.cache		= eth_header_cache,
 	.cache_update	= eth_header_cache_update,
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index a81dae8..492e580 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -845,7 +845,6 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
 
 	ph.raw = frame;
 
-	skb->protocol = proto;
 	skb->dev = dev;
 	skb->priority = po->sk.sk_priority;
 	skb->mark = po->sk.sk_mark;
@@ -924,6 +923,14 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
 		len = ((to_write > len_max) ? len_max : to_write);
 	}
 
+	if (proto == htons(ETH_P_ALL) && dev->header_ops->get_protocol) {
+		skb->protocol = dev->header_ops->get_protocol(dev, skb);
+		if (unlikely(skb->protocol == htons(ETH_P_ALL)))
+			return -EINVAL;
+	} else {
+		skb->protocol = proto;
+	}
+
 	return tp_len;
 }
 
@@ -1113,7 +1120,13 @@ static int packet_snd(struct socket *sock,
 	if (err)
 		goto out_free;
 
-	skb->protocol = proto;
+	if (proto == htons(ETH_P_ALL) && dev->header_ops->get_protocol) {
+		skb->protocol = dev->header_ops->get_protocol(dev, skb);
+		if (unlikely(skb->protocol == htons(ETH_P_ALL)))
+			return -EINVAL;
+	} else {
+		skb->protocol = proto;
+	}
 	skb->dev = dev;
 	skb->priority = sk->sk_priority;
 	skb->mark = sk->sk_mark;

-- 
MST