flow_dissector: introduce programable flow_dissector

Introduce dissector infrastructure which allows user to specify which
parts of skb he wants to dissect.
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/flow_dissector.h

 #ifndef _NET_FLOW_DISSECTOR_H
 #define _NET_FLOW_DISSECTOR_H
 
+/**
+ * struct flow_dissector_key_basic:
+ * @thoff: Transport header offset
+ * @n_proto: Network header protocol (eg. IPv4/IPv6)
+ * @ip_proto: Transport header protocol (eg. TCP/UDP)
+ */
+struct flow_dissector_key_basic {
+	u16	thoff;
+	__be16	n_proto;
+	u8	ip_proto;
+};
+
+/**
+ * struct flow_dissector_key_addrs:
+ * @src: source ip address in case of IPv4
+ *	 For IPv6 it contains 32bit hash of src address
+ * @dst: destination ip address in case of IPv4
+ *	 For IPv6 it contains 32bit hash of dst address
+ */
+struct flow_dissector_key_addrs {
+	/* (src,dst) must be grouped, in the same way than in IP header */
+	__be32 src;
+	__be32 dst;
+};
+
+/**
+ * flow_dissector_key_tp_ports:
+ *	@ports: port numbers of Transport header
+ *		port16[0]: src port number
+ *		port16[1]: dst port number
+ */
+struct flow_dissector_key_ports {
+	union {
+		__be32 ports;
+		__be16 port16[2];
+	};
+};
+
+enum flow_dissector_key_id {
+	FLOW_DISSECTOR_KEY_BASIC, /* struct flow_dissector_key_basic */
+	FLOW_DISSECTOR_KEY_IPV4_ADDRS, /* struct flow_dissector_key_addrs */
+	FLOW_DISSECTOR_KEY_IPV6_HASH_ADDRS, /* struct flow_dissector_key_addrs */
+	FLOW_DISSECTOR_KEY_PORTS, /* struct flow_dissector_key_ports */
+
+	FLOW_DISSECTOR_KEY_MAX,
+};
+
+struct flow_dissector_key {
+	enum flow_dissector_key_id key_id;
+	size_t offset; /* offset of struct flow_dissector_key_*
+			  in target the struct */
+};
+
+struct flow_dissector {
+	unsigned int used_keys; /* each bit repesents presence of one key id */
+	unsigned short int offset[FLOW_DISSECTOR_KEY_MAX];
+};
+
 /* struct flow_keys:
  *	@src: source ip address in case of IPv4
  *	      For IPv6 it contains 32bit hash of src address
@@ -27,6 +85,9 @@ struct flow_keys {
 	u8	ip_proto;
 };
 
+void skb_flow_dissector_init(struct flow_dissector *flow_dissector,
+			     const struct flow_dissector_key *key,
+			     unsigned int key_count);
 bool __skb_flow_dissect(const struct sk_buff *skb, struct flow_keys *flow,
 			void *data, __be16 proto, int nhoff, int hlen);
 

net/core/flow_dissector.c

+#include <linux/kernel.h>
 #include <linux/skbuff.h>
 #include <linux/export.h>
 #include <linux/ip.h>
@@ -15,6 +16,53 @@
 #include <net/flow_dissector.h>
 #include <scsi/fc/fc_fcoe.h>
 
+static bool skb_flow_dissector_uses_key(struct flow_dissector *flow_dissector,
+					enum flow_dissector_key_id key_id)
+{
+	return flow_dissector->used_keys & (1 << key_id);
+}
+
+static void skb_flow_dissector_set_key(struct flow_dissector *flow_dissector,
+				       enum flow_dissector_key_id key_id)
+{
+	flow_dissector->used_keys |= (1 << key_id);
+}
+
+static void *skb_flow_dissector_target(struct flow_dissector *flow_dissector,
+				       enum flow_dissector_key_id key_id,
+				       void *target_container)
+{
+	return ((char *) target_container) + flow_dissector->offset[key_id];
+}
+
+void skb_flow_dissector_init(struct flow_dissector *flow_dissector,
+			     const struct flow_dissector_key *key,
+			     unsigned int key_count)
+{
+	unsigned int i;
+
+	memset(flow_dissector, 0, sizeof(*flow_dissector));
+
+	for (i = 0; i < key_count; i++, key++) {
+		/* User should make sure that every key target offset is withing
+		 * boundaries of unsigned short.
+		 */
+		BUG_ON(key->offset > USHRT_MAX);
+		BUG_ON(skb_flow_dissector_uses_key(flow_dissector,
+						   key->key_id));
+
+		skb_flow_dissector_set_key(flow_dissector, key->key_id);
+		flow_dissector->offset[key->key_id] = key->offset;
+	}
+
+	/* Ensure that the dissector always includes basic key. That way
+	 * we are able to avoid handling lack of it in fast path.
+	 */
+	BUG_ON(!skb_flow_dissector_uses_key(flow_dissector,
+					    FLOW_DISSECTOR_KEY_BASIC));
+}
+EXPORT_SYMBOL(skb_flow_dissector_init);
+
 /* copy saddr & daddr, possibly using 64bit load/store
  * Equivalent to :	flow->src = iph->saddr;
  *			flow->dst = iph->daddr;