[V2,5/5] examples/pipeline: add variable size headers example

diff --git a/examples/pipeline/examples/varbit.cli b/examples/pipeline/examples/varbit.cli
new file mode 100644
index 0000000000..0589e32c15
--- /dev/null
+++ b/examples/pipeline/examples/varbit.cli
@@ -0,0 +1,35 @@ 
+; SPDX-License-Identifier: BSD-3-Clause
+; Copyright(c) 2020 Intel Corporation
+
+;
+; Customize the LINK parameters to match your setup.
+;
+mempool MEMPOOL0 buffer 2304 pool 32K cache 256 cpu 0
+
+link LINK0 dev 0000:18:00.0 rxq 1 128 MEMPOOL0 txq 1 512 promiscuous on
+link LINK1 dev 0000:18:00.1 rxq 1 128 MEMPOOL0 txq 1 512 promiscuous on
+link LINK2 dev 0000:3b:00.0 rxq 1 128 MEMPOOL0 txq 1 512 promiscuous on
+link LINK3 dev 0000:3b:00.1 rxq 1 128 MEMPOOL0 txq 1 512 promiscuous on
+
+;
+; PIPELINE0 setup.
+;
+pipeline PIPELINE0 create 0
+
+pipeline PIPELINE0 port in 0 link LINK0 rxq 0 bsz 32
+pipeline PIPELINE0 port in 1 link LINK1 rxq 0 bsz 32
+pipeline PIPELINE0 port in 2 link LINK2 rxq 0 bsz 32
+pipeline PIPELINE0 port in 3 link LINK3 rxq 0 bsz 32
+
+pipeline PIPELINE0 port out 0 link LINK0 txq 0 bsz 32
+pipeline PIPELINE0 port out 1 link LINK1 txq 0 bsz 32
+pipeline PIPELINE0 port out 2 link LINK2 txq 0 bsz 32
+pipeline PIPELINE0 port out 3 link LINK3 txq 0 bsz 32
+pipeline PIPELINE0 port out 4 sink none
+
+pipeline PIPELINE0 build ./examples/pipeline/examples/varbit.spec
+
+;
+; Pipelines-to-threads mapping.
+;
+thread 1 pipeline PIPELINE0 enable
diff --git a/examples/pipeline/examples/varbit.spec b/examples/pipeline/examples/varbit.spec
new file mode 100644
index 0000000000..cd49403fa9
--- /dev/null
+++ b/examples/pipeline/examples/varbit.spec
@@ -0,0 +1,95 @@ 
+; SPDX-License-Identifier: BSD-3-Clause
+; Copyright(c) 2020 Intel Corporation
+
+; This simple example illustrates how to work with variable size headers. The assumed input packet
+; is Ethernet/IPv4/UDP, with the IPv4 header containing between 0 and 40 bytes of options. To locate
+; the start of the UDP header, the size of the IPv4 header needs to be detected first, which is done
+; by reading the first byte of the IPv4 header that carries the 4-bit Internet Header Length (IHL)
+; field; this read is done with the "lookahead" instruction, which does not advance the extract
+; pointer within the input packet buffer. Once the size of the IPv4 header options is known for the
+; current packet, the IPv4 header is extracted by using the two-argument "extract" instruction. Then
+; the UDP header is extracted and modified.
+
+//
+// Headers
+//
+struct ethernet_h {
+	bit<48> dst_addr
+	bit<48> src_addr
+	bit<16> ethertype
+}
+
+struct ipv4_top_h {
+	bit<8> ver_ihl
+}
+
+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
+	varbit<320> options
+}
+
+struct udp_h {
+	bit<16> src_port
+	bit<16> dst_port
+	bit<16> length
+	bit<16> checksum
+}
+
+header ethernet instanceof ethernet_h
+header ipv4_top instanceof ipv4_top_h
+header ipv4 instanceof ipv4_h
+header udp instanceof udp_h
+
+//
+// Meta-data
+//
+struct metadata_t {
+	bit<32> port
+	bit<32> options_size
+}
+
+metadata instanceof metadata_t
+
+//
+// Pipeline.
+//
+apply {
+	rx m.port
+
+	// Extract the fixed size Ethernet header.
+	extract h.ethernet
+
+	// Extract the variable size IPv4 header with up to 10 options.
+	lookahead h.ipv4_top
+	mov m.options_size h.ipv4_top.ver_ihl
+	and m.options_size 0xF
+	sub m.options_size 5
+	shl m.options_size 2
+	extract h.ipv4 m.options_size
+
+	// Extract the fixed size UDP header.
+	extract h.udp
+
+	// Modify the UDP header.
+	mov h.udp.src_port 0xAABB
+	mov h.udp.dst_port 0xCCDD
+
+	// Decide the output port.
+	xor m.port 1
+
+	// Emit the Ethernet, IPv4 and UDP headers.
+	emit h.ethernet
+	emit h.ipv4
+	emit h.udp
+
+	tx m.port
+}