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SubjectRe: [PATCH] net: packet: option to only pass skb protocol
On Tue, Jan 05, 2010 at 03:51:50PM -0800, David Miller wrote:
> From: "Chris Friesen" <cfriesen@nortel.com>
> 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


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