; SPDX-License-Identifier: BSD-3-Clause
; Copyright(c) 2020 Intel Corporation

; The learner tables are very useful for learning and connection tracking.
;
; As opposed to regular tables, which are read-only for the data plane, the learner tables can be
; updated by the data plane without any control plane intervention. The "learning" process typically
; takes place by having the default action (i.e. the table action which is executed on lookup miss)
; explicitly add to the table with a specific action the key that just missed the lookup operation.
; Each table key expires automatically after a configurable timeout period if not hit during this
; interval.
;
; This example demonstrates a simple connection tracking setup, where the connections are identified
; by the IPv4 destination address. The forwarding action assigned to each new connection gets the
; output port as argument, with the output port of each connection generated by a counter that is
; persistent between packets. On top of the usual table stats, the learner table stats include the
; number of packets with learning related events.

//
// Headers
//
struct ethernet_h {
	bit<48> dst_addr
	bit<48> src_addr
	bit<16> ethertype
}

struct ipv4_h {
	bit<8> ver_ihl
	bit<8> diffserv
	bit<16> total_len
	bit<16> identification
	bit<16> flags_offset
	bit<8> ttl
	bit<8> protocol
	bit<16> hdr_checksum
	bit<32> src_addr
	bit<32> dst_addr
}

header ethernet instanceof ethernet_h
header ipv4 instanceof ipv4_h

//
// Meta-data
//
struct metadata_t {
	bit<32> port_in
	bit<32> port_out

	// Arguments for the "fwd_action" action.
	bit<32> fwd_action_arg_port_out
}

metadata instanceof metadata_t

//
// Registers.
//
regarray counter size 1 initval 0

//
// Actions
//
struct fwd_action_args_t {
	bit<32> port_out
}

action fwd_action args instanceof fwd_action_args_t {
	mov m.port_out t.port_out
	return
}

action learn_action args none {
	// Read current counter value into m.fwd_action_arg_port_out.
	regrd m.fwd_action_arg_port_out counter 0

	// Increment the counter.
	regadd counter 0 1

	// Limit the output port values to 0 .. 3.
	and m.fwd_action_arg_port_out 3

	// Add the current lookup key to the table with fwd_action as the key action. The action
	// arguments are read from the packet meta-data (the m.fwd_action_arg_port_out field). These
	// packet meta-data fields have to be written before the "learn" instruction is invoked.
	learn fwd_action m.fwd_action_arg_port_out

	// Send the current packet to the same output port.
	mov m.port_out m.fwd_action_arg_port_out

	return
}

//
// Tables.
//
learner fwd_table {
	key {
		h.ipv4.dst_addr
	}

	actions {
		fwd_action

		learn_action
	}

	default_action learn_action args none

	size 1048576

	timeout 120
}

//
// Pipeline.
//
apply {
	rx m.port_in
	extract h.ethernet
	extract h.ipv4
	table fwd_table
	emit h.ethernet
	emit h.ipv4
	tx m.port_out
}