net: Move fou_build_header into fou.c and refactor

Move fou_build_header out of ip_tunnel.c and into fou.c splitting
it up into fou_build_header, gue_build_header, and fou_build_udp.
This allows for other users for TX of FOU or GUE. Change ip_tunnel_encap
to call fou_build_header or gue_build_header based on the tunnel
encapsulation type. Similarly, added fou_encap_hlen and gue_encap_hlen
functions which are called by ip_encap_hlen. New net/fou.h has
prototypes and defines for this.

Added NET_FOU_IP_TUNNELS configuration. When this is set, IP tunnels
can use FOU/GUE and fou module is also selected.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 26 insertions, 0 deletions

diff --git a/include/net/fou.h b/include/net/fou.h
new file mode 100644
index 0000000..cf4ce88
--- /dev/null
+++ b/include/net/fou.h
@@ -0,0 +1,26 @@
+#ifndef __NET_FOU_H
+#define __NET_FOU_H
+
+#include <linux/skbuff.h>
+
+#include <net/flow.h>
+#include <net/gue.h>
+#include <net/ip_tunnels.h>
+#include <net/udp.h>
+
+int fou_build_header(struct sk_buff *skb, struct ip_tunnel_encap *e,
+		     u8 *protocol, struct flowi4 *fl4);
+int gue_build_header(struct sk_buff *skb, struct ip_tunnel_encap *e,
+		     u8 *protocol, struct flowi4 *fl4);
+
+static size_t fou_encap_hlen(struct ip_tunnel_encap *e)
+{
+	return sizeof(struct udphdr);
+}
+
+static size_t gue_encap_hlen(struct ip_tunnel_encap *e)
+{
+	return sizeof(struct udphdr) + sizeof(struct guehdr);
+}
+
+#endif