+ u32 tunnel_type; /* Put the TNL_T_PROTO_* type in here. */
+ u8 ipproto; /* The IP protocol for the tunnel. */
+
+ /*
+ * Returns the length of the tunnel header that will be added in
+ * build_header() (i.e. excludes the IP header). Returns a negative
+ * error code if the configuration is invalid.
+ */
+ int (*hdr_len)(const struct tnl_mutable_config *);
+
+ /*
+ * Builds the static portion of the tunnel header, which is stored in
+ * the header cache. In general the performance of this function is
+ * not too important as we try to only call it when building the cache
+ * so it is preferable to shift as much work as possible here. However,
+ * in some circumstances caching is disabled and this function will be
+ * called for every packet, so try not to make it too slow.
+ */
+ void (*build_header)(const struct vport *,
+ const struct tnl_mutable_config *, void *header);
+
+ /*
+ * Updates the cached header of a packet to match the actual packet
+ * data. Typical things that might need to be updated are length,
+ * checksum, etc. The IP header will have already been updated and this
+ * is the final step before transmission. Returns a linked list of
+ * completed SKBs (multiple packets may be generated in the event
+ * of fragmentation).
+ */
+ struct sk_buff *(*update_header)(const struct vport *,
+ const struct tnl_mutable_config *,
+ struct dst_entry *, struct sk_buff *);
+};
+
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,20)
+/*
+ * On these kernels we have a fast mechanism to tell if the ARP cache for a
+ * particular destination has changed.
+ */
+#define HAVE_HH_SEQ
+#endif
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,27)
+/*
+ * On these kernels we have a fast mechanism to tell if the routing table
+ * has changed.
+ */
+#define HAVE_RT_GENID
+#endif
+#if !defined(HAVE_HH_SEQ) || !defined(HAVE_RT_GENID)
+/* If we can't detect all system changes directly we need to use a timeout. */
+#define NEED_CACHE_TIMEOUT
+#endif
+struct tnl_cache {
+ struct rcu_head rcu;