Add dpapp README.md

.wordlist.txt

@@ -559,6 +559,7 @@ sai
 saic
 SAIC
 saichallenger
+saidashdpapp
 saigen
 sairedis
 SAIRPC

dash-pipeline/dpapp/README.md

@@ -0,0 +1,84 @@
+# DPAPP - Data Plane Application
+## Overview
+DPAPP fulfills [VPP](https://fd.io/) plugin mechanism to implement the slow (exception) path of
+packet processing. It works with [DASH pipeline BMv2](https://github.com/sonic-net/DASH/tree/main/dash-pipeline/bmv2),
+serving fast path, to consist of a complete DASH data plane. Refer to the doc
+[bmv2 data plane app](https://github.com/sonic-net/DASH/blob/main/documentation/dataplane/dash-bmv2-data-plane-app.md)
+for design details.
+
+## Usage
+1. build dpapp
+```
+DASH/dash-pipeline$ make dpapp
+```
+2. Run dpapp
+```
+DASH/dash-pipeline$ make run-dpapp
+```
+
+## Debug
+VPP CLI `vppctl` provides lots of commands for debugging. Use the command `docker exec -it dash-dpapp-${USER} vppctl`
+to launch it.
+
+- Check dpapp interfaces and the counters
+```
+vpp# show interface
+              Name               Idx    State  MTU (L3/IP4/IP6/MPLS)     Counter          Count
+host-veth5                        1      up          9000/0/0/0     rx packets                    39
+                                                                    rx bytes                   10764
+                                                                    tx packets                    39
+                                                                    tx bytes                    7628
+local0                            0     down          0/0/0/0
+
+vpp# show hardware-interfaces
+              Name                Idx   Link  Hardware
+host-veth5                         1     up   host-veth5
+  Link speed: unknown
+  RX Queues:
+    queue thread         mode
+    0     vpp_wk_0 (1)   interrupt
+  TX Queues:
+    TX Hash: [name: hash-eth-l34 priority: 50 description: Hash ethernet L34 headers]
+    queue shared thread(s)
+    0     yes    0-1
+  Ethernet address 02:fe:23:f0:88:99
+  Linux PACKET socket interface v3
+  FEATURES:
+    qdisc-bpass-enabled
+    cksum-gso-enabled
+  RX Queue 0:
+    block size:65536 nr:160  frame size:2048 nr:5120 next block:39
+  TX Queue 0:
+    block size:69206016 nr:1  frame size:67584 nr:1024 next frame:39
+    available:1024 request:0 sending:0 wrong:0 total:1024
+local0                             0    down  local0
+  Link speed: unknown
+  local
+
+```
+
+- Check flow table in dpapp
+```
+vpp# show dash flow
+     1: eni 00:cc:cc:cc:cc:cc, vnet_id 343, proto 17, 10.1.1.10 1234 -> 10.1.2.50 80
+        common data - version 0, direction 1, actions 0x9, timeout 28
+
+vpp# clear dash flow 1
+```
+
+- Check packet processing trace in dpapp
+```
+vpp# trace add af-packet-input 100
+vpp# show trace
+```
+
+On behalf of BMv2 switch, script `tools/send_p2a_pkt.py` can send packet with dash header to verify basic flow
+functionality of dpapp.
+
+## Test
+By default, flow lookup is not enabled in DASH pipeline. The decorator `@use_flow` will enable it and then involve dpapp
+for slow path. If test cases are verified to support flow, aka stateful packet processing, use the decorator to mark
+the test class.
+
+PTF test script [saidashdpapp_sanity.py](https://github.com/sonic-net/DASH/blob/main/test/test-cases/functional/ptf/saidashdpapp_sanity.py)
+provides sanity check for dpapp. Refer to it as a sample for new flow tests.