p4tc-dev · vbnogueira · Oct 7, 2024
diff --git a/drop_reason/Makefile b/drop_reason/Makefile
@@ -0,0 +1,36 @@
+## call with make PROG=xxx to build
+##  make PROG=xxx clean|generate|realclean
+#
+## Argument for the CLANG compiler
+CLANG ?= clang
+P4C_PNA_P4TC ?= p4c-pna-p4tc
+PROG ?= drop_reason
+#we need to have a headers package instead of this..
+INCLUDES= -I../include
+# Optimization flags to save space
+CFLAGS+= -O1 -g -c -D__KERNEL__ -D__ASM_SYSREG_H -DBTF \
+	 -Wno-unused-value  -Wno-pointer-sign \
+	 -Wno-compare-distinct-pointer-types \
+	 -Wno-gnu-variable-sized-type-not-at-end \
+	 -Wno-address-of-packed-member -Wno-tautological-compare \
+	 -Wno-unknown-warning-option -Wnoparentheses-equality
+
+TMPL+=generated/$(PROG).template
+TMPL+=generated/$(PROG).json
+SRCS+=generated/$(PROG)_parser.c
+SRCS+=generated/$(PROG)_control_blocks.c
+OBJS=$(SRCS:.c=.o)
+all: $(OBJS)
+
+$(OBJS): %.o : %.c
+	$(CLANG) $(CFLAGS) $(INCLUDES) --target=bpf -mcpu=probe -c $< -o $@
+
+# Disable uninitialized_use because compiler is emitting a false positive in the parser
+generate:
+	$(P4C_PNA_P4TC) $(PROG).p4 --Wdisable=uninitialized_use -o generated
+
+clean:
+	rm -f $(OBJS)
+
+realclean:
+	rm -f $(OBJS) $(SRCS) $(TMPL) $(PROG)_parser.h
diff --git a/drop_reason/README.md b/drop_reason/README.md
@@ -0,0 +1,326 @@
+# Drop Reason
+
+This program demonstrates how to capture events from the datapath and log them as events to the control plane.
+In this case we capture the reason why packets are dropped, what port they arrived on and what src mac address was observed on the packet.
+Packets could be dropped for two reasons:
+
+- The parser was unable to parse the packet
+- Unable to find a matching entry on lookup of table nh\_table.
+
+The *drop_reason* program first parses ethernet <u>ipv4</u> packets.
+Any other packets are rejected and will result in a drop_reason digest event being sent with the packet's `ingress_port`, src mac address and drop reason set to `parser_rejected`.
+After the parser recognizes an ipv4 packet, the src ip address is used as a lookup
+key for table *nh_table*. On a table hit, the programmed action *send_nh(port, srcMac, dstMac)* instance is executed.
+The action first sets the src and destination mac address, then redirects the packet to a specified port.
+On a table miss, the program sets the `ingress_port`, `send_digest` to true, drop reason to `table_miss` and marks the packet to be dropped.
+`my_ingress_metadata_t` will hold the port on where the packet arrived, the drop reason and `send_digest`.
+`send_digest` signals the deparser to send a digest message to user space.
+This digest message will hold the source mac address, the port where the packet arrived and the drop reason:
+
+```
+struct mac_learn_digest_t {
+    @tc_type("macaddr") bit<48> srcAddr;
+    @tc_type("dev") PortId_t ingress_port;
+    DROP_REASON drop_reason;
+};
+```
+
+## Setup Requirements
+
+Make sure that the p4node basic container has already been created at this point(as per instructions found in [p4node](https://github.com/p4tc-dev/p4tc-examples-pub.git)). To run the sample described setup here requires 5 terminals, four terminals inside the container and one on the VM side to generate traffic.
+
+### Terminal 1 (observation of tc commands on p4node).
+
+Enter the container p4node:
+
+`sudo ip netns exec p4node /bin/bash`
+
+setup path for TC binary
+
+`TC="/usr/sbin/tc"`
+
+setup the path to where the json introspection file can be found..
+
+```
+cd /home/vagrant/p4tc-examples-pub/drop_reason/generated
+export INTROSPECTION=.
+```
+run TC monitor:
+`$TC mon p4 events`
+
+### Terminal 2 (observation of p4 digest events on p4node).
+
+First enter the container and make sure you have the introspection path setup
+
+Enter the container p4node:
+
+`sudo ip netns exec p4node /bin/bash`
+
+setup path for TC binary
+
+`TC="/usr/sbin/tc"`
+
+setup the path to where the json introspection file can be found..
+
+```
+cd /home/vagrant/p4tc-examples-pub/drop_reason/generated
+export INTROSPECTION=.
+```
+
+run TC monitor for digest events:
+`$TC mon p4 digest`
+
+### Terminal 3 (observes incoming traffic into p4node)
+
+First enter the container and make sure you have the introspection path setup
+
+`sudo ip netns exec p4node /bin/bash`
+
+Now let's listen to traffic on port0
+
+```
+DEV=port0
+tcpdump -n -i $DEV -e
+```
+
+### Terminal 4 (to instantiate and runtime control the program)
+
+We will run commands to first load the prog and then do required runtime setup.
+
+First enter the container
+
+```
+sudo ip netns exec p4node /bin/bash
+cd /home/vagrant/p4tc-examples-pub/drop_reason
+```
+
+Compile the parser and control blocks programs if you have not already
+
+`make`
+
+Make sure you have the introspection path setup and load the *digest* program
+
+```
+cd generated
+export INTROSPECTION=.
+TC="/usr/sbin/tc"
+./drop_reason.template
+```
+
+now instantiate the prog
+
+```
+$TC filter add block 21 ingress protocol all prio 10 p4 pname drop_reason \
+action bpf obj drop_reason_parser.o section p4tc/parse \
+action bpf obj drop_reason_control_blocks.o section p4tc/main
+```
+
+### Terminal 5 (on the VM side)
+
+Try sending a message of packets which will be dropped by the parser ..
+
+`ping -I p4port0 10.0.1.2 -c 1`
+
+Let's check some stats, below shows 3 packets dropped by the parser on <u>terminal 3</u>:
+
+```
+$TC -s filter ls block 21 ingress
+filter protocol all pref 10 p4 chain 0
+filter protocol all pref 10 p4 chain 0 handle 0x1 pname drop_reason
+	action order 1: bpf drop_reason_parser.o:[p4tc/parse] id 92 name tc_parse_func tag 1bd66321c5ad54e4 jited default-action pipe
+	index 1 ref 1 bind 1 installed 590 sec used 293 sec firstused 295 sec
+	Action statistics:
+	Sent 84 bytes 3 pkt (dropped 3, overlimits 0 requeues 0)
+	backlog 0b 0p requeues 0
+
+	action order 2: bpf drop_reason_control_blocks.o:[p4tc/main] id 94 name tc_ingress_func tag 42e6e971daa41152 jited default-action pipe
+	 index 2 ref 1 bind 1 installed 590 sec used 590 sec
+	Action statistics:
+	Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
+	backlog 0b 0p requeues 0
+```
+
+On <u>terminal 2</u> look for the digest event:
+
+```
+total exts 0
+Added extern 
+        extern order 1:
+          Extern kind Digest
+          Extern instance Ingress_Deparser.digest_inst
+          Extern key 0
+          Params:
+
+          srcAddr  id 2 type macaddr value: 10:00:00:01:aa:bb
+          ingress_port  id 3 type dev value: port0
+          drop_reason  id 4 type bit8  value: 1
+`` 
+
+drop_reason `1` means `PARSER_REJECTED`
+
+Back on terminal 5, generate a TCP packet:
+
+`sudo /home/vagrant/sendpacket/sendpacket.py /home/vagrant/p4tc-examples-pub/drop_reason/testpkt.yml`
+
+Again on <u>terminal 2</u> look for the digest event:
+
+```
+total exts 0
+Added extern 
+        extern order 1:
+          Extern kind Digest
+          Extern instance Ingress_Deparser.digest_inst
+          Extern key 0
+          Params:
+
+          srcAddr  id 2 type macaddr value: 02:03:04:05:06:01
+          ingress_port  id 3 type dev value: port0
+          drop_reason  id 4 type bit8  value: 2
+```
+
+This time the drop_reason is set to `2`, which means `TABLE_MISS`
+
+Ok, back on <u>terminal 4</u> let's create an entry to match on the dst address *10.0.0.2* and rewrite the src mac to *00:01:02:03:04:05* and dst mac *06:07:08:09:11:12* then send out on *port1*
+
+```
+$TC p4ctrl create drop_reason/table/ingress/nh_table \
+dstAddr 10.0.0.2 \
+action send_nh param port port1 param srcMac 06:07:08:09:11:12 param dstMac 00:01:02:03:04:05
+```
+
+If you look at <u>terminal 1</u>, a table create event will be emitted:
+
+```
+created pipeline:  drop_reason(id 1)
+ table: ingress/nh_table(id 1)entry priority 64000[permissions -RUD-PS-R--X--]
+    entry key
+     dstAddr id:1 size:32b type:ipv4 exact fieldval  10.0.0.2/32
+    entry actions:
+        action order 1: drop_reason/ingress/send_nh  index 2 ref 1 bind 1
+         params:
+          port type dev  value: port1 id 1
+
+          srcMac type macaddr  value: 06:07:08:09:11:12 id 2
+
+          dstMac type macaddr  value: 00:01:02:03:04:05 id 3
+
+
+    created by entity: tc (id 2)
+    create by pid: 3921
+    created by process: tc
+    dynamic false
+
+    tmpl created false
+```
+
+On <u>terminal 4</u> watch *port1* traffic (recall that you are watching incoming traffic on <u>terminal 2</u> on *port0*):
+
+`tcpdump -n -i port1 -e`
+
+Now you can send the rewritten mac address when you generate traffic on terminal 5 as follows:
+
+`sudo /home/vagrant/sendpacket/sendpacket.py /home/vagrant/p4tc-examples-pub/drop_reason/testpkt.yml`
+
+Back on <u>terminal 4<\u>:
+
+```
+21:32:09.362397 06:07:08:09:11:12 > 00:01:02:03:04:05, ethertype IPv4 (0x0800), length 54: 10.0.0.1.1235 > 10.0.0.2.4321: Flags [S], seq 0, win 8192, length 0
+```
+
+## General help on runtime CLI
+
+First just dump all possible tables in this program
+
+*$TC p4ctrl create drop_reason/table help*
+
+```
+Tables for pipeline drop_reason:
+	  table name ingress/nh_table
+	  table id 1
+```
+
+As we can see, there is only one with a path ingress/nh_table
+
+Now let's get help on the *create* command for this table:
+
+*$TC p4ctrl create drop_reason/table/ingress/nh_table help*
+
+```
+Key fields for table nh_table:
+	 key name dstAddr
+	 key id 1
+	 key type ipv4
+	 key match type 	 exact
+
+Actions for table nh_table:
+	  act name ingress/send_nh
+	  act id 1
+
+	  Params for ingress/send_nh:
+	    param name port
+	    param id 1
+	    param type dev
+
+	    param name srcMac
+	    param id 2
+	    param type macaddr
+
+	    param name dstMac
+	    param id 3
+	    param type macaddr
+
+          act name ingress/drop
+          act id 2
+```
+
+Above is indicating the table has a key called dstAddr which is of type ipv4 address and that it takes one action:
+  - *send_nh* which takes 3 params 1)*port*, a linux netdev 2) *srcMac*, a mac address 3) *dstMac*, also a mac address
+
+And help on the *delete* command:
+
+*$TC p4ctrl delete drop_reason/table/ingress/nh_table help*
+
+```
+Key fields for table nh_table:
+	 key name dstAddr
+	 key id 1
+	 key type ipv4
+	 key match type  exact
+```
+
+This shows the key name "dstAddr" as an exact IPv4 address.
+Example to delete the entry we created:
+
+*$TC p4ctrl delete drop_reason/table/ingress/nh_table dstAddr 10.0.0.2*
+
+And to delete/flush the whole table:
+
+*$TC p4ctrl delete drop_reason/table/ingress/nh_table
+
+And help on the *get* command:
+
+*$TC p4ctrl get drop_reason/table/ingress/nh_table help*
+
+```
+Key fields for table nh_table:
+	 key name dstAddr
+	 key id 1
+	 key type ipv4
+	 key match type 	 exact
+```
+
+This shows the key name "dstAddr" as an exact IPv4 address.
+For example to retrieve the entry we created using our key of 10.0.0.2:
+
+*$TC p4ctrl get drop_reason/table/ingress/nh_table dstAddr 10.0.0.2*
+
+Note, we can dump the whole table as such:
+
+*$TC p4ctrl get drop_reason/table/ingress/nh_table*
+
+
+To cleanup
+----------
+To clean up you need to run the following script on Terminal 4, where the template was installed and the program was instantiated:
+
+`./drop_reason.purge`