Linux Network Programming with P4

1 .Linux Network Programming with P4 Linux Plumbers 2018 Fabian Ruffy, William Tu, Mihai Budiu VMware Inc. and University of British Columbia 

2 .Outline • Introduction to P4 • XDP and the P4 Compiler Fabian • Testing • Example • Performance Results William • Discussion 2 

3 .What is P4? • High-level programming language for network data planes • Allows for protocol flexibility • Specifies a packet processing pipeline • Compiled and loaded into target platform • Open and standardized P4: Programming Protocol-Independent Packet Processors Pat Bosshart, Dan Daly, Glen Gibb, Martin Izzard, Nick McKeown, Jennifer Rexford, Cole Schlesinger, Dan Talayco, Amin Vahdat, George Varghese, David Walker ACM SIGCOMM Computer Communications Review (CCR). Volume 44, Issue #3 (July 2014) 3 

4 .P4 Essentials • C-like, strongly typed language • Type and memory-safe (no pointers) • Bounded execution (no loops) • Statically allocated (no malloc, no recursion) • Spec: http://github.com/p4lang/p4-spec • Reference compiler implementation: http://github.com/p4lang/p4c (Apache 2 license) 4 

5 .P4 Software Workflow P4 Compiler P4 Architecture Model Target Supplied 5 

6 .P4 Software Workflow User-supplied P4 Program P4 Compiler P4 Architecture Model Target Supplied 5 

7 .P4 Software Workflow User-supplied P4 Program P4 Compiler P4 Architecture Model Target Supplied 5 

8 .P4 Software Workflow User-supplied P4 Program P4 Compiler P4 Architecture Target-specific Model configuration binary Target Supplied 5 

9 .P4 Software Workflow User-supplied P4 Program P4 Compiler P4 Architecture Target-specific Extern configuration Load Tables Data Plane Model objects binary Target Supplied 5 

10 .P4 Software Workflow User-supplied Control Plane P4 Program P4 Compiler P4 Architecture Target-specific Extern configuration Load Tables Data Plane Model objects binary Target Supplied 5 

11 .P4 Software Workflow User-supplied Control Plane RUNTIME P4 Program P4 Compiler Add/remove Extern Packet-in/out table entries control CPU port P4 Architecture Target-specific Extern configuration Load Tables Data Plane Model objects binary Target Supplied 5 

12 .P416 generic data-plane model os_lib.p4 switch_lib.p4 npu_lib.p4 nic_lib.p4 The networking stack of the OS program.p4 6 

13 .P4 and XDP 7 

14 .eBPF/XDP • Virtual machine running in the Linux kernel User space Kernel socket • Provides: space • The ability to write restricted C and run it in the kernel IP/routing • A set of kernel hook points invoking the eBPF program Bridge hook • Extensible, safe and fast • Alternative to user-space networking Your tc Program driver eBPF hook point Hardware Example of TC+eBPF 8 

15 .eBPF/XDP • Virtual machine running in the Linux kernel User space Kernel socket • Provides: space • The ability to write restricted C and run it in the kernel IP/routing • A set of kernel hook points invoking the eBPF program Bridge hook • Extensible, safe and fast • Alternative to user-space networking Your tc Program driver eBPF hook point Hardware A programmable data plane in the Linux kernel! Example of TC+eBPF 8 

16 . P4 vs eBPF/XDP Feature P4 eBPF/XDP Level High Low Safe Yes Yes Safety Type system Verifier Loops In parsers Tail calls (dynamic limit) Resources Statically allocated Statically allocated Policies Tables (match+action) Maps (tables) Extern helpers Target-specific Hook-specific Control-plane API Synthesized by compiler eBPF maps 9 

17 .The P4 eBPF backends • p4c-ebpf is part of the open-source distribution • http://github.com/p4lang/p4c/backends/ebpf • p4c-xdp is a separate open-source project • http://github.com/vmware/p4c-xdp • Extension of the p4c compiler • Reuses much of the code • Not production-ready • Needs more work p4c-xdp • Known bugs and limitations p4c-ebpf • Generated not efficient yet 10 

18 .Generating XDP code 11 

19 .P416 -> C -> eBPF/XDP • Generates stylized C • No tail calls yet, all data on stack • eBPF tables control/data-plane communication • Can do filtering, forwarding, encapsulation • Relies on Linux TC for forwarding • We plan on switching to libbpf 12 

20 .The XDP Switching Model Control-plane API Drop/Forward/Pass Input port EBPF tables packet in packet out Match+ Parser Deparser Action headers headers XDP Data Plane 13 

21 . Flow app.p4 User space BPF system call Kernel space exe Match-Action tables Data Plane XDP driver Hardware 14 

22 . Flow app.p4 p4c-xdp app.c User space BPF system call Kernel space exe Match-Action tables Data Plane XDP driver Hardware 14 

23 . Flow app.p4 p4c-xdp app.c Clang + User space LLVM BPF system call Kernel space app.o Verifier exe Match-Action tables Data Plane XDP driver Hardware 14 

24 . Flow control-plane.c app.p4 p4c-xdp app.h Control-plane API app.c Clang + User space LLVM BPF system call Kernel space app.o Verifier exe Match-Action tables Data Plane XDP driver Hardware 14 

25 .Testing P4-XDP code 15 

26 .Test Frameworks • User-space testing • Isolates specification from implementation • Validates correctness of generated code • User-space wrappers around eBPF tables and APIs • Reads and writes packets from capture files • Kernel-space testing • Loads eBPF program into kernel • I/O connected to virtual interfaces • Writes capture files to interfaces in user-space • Records output using tcpdump 16 

27 . Five Testing Stages test.p4 test.stf 17 

28 . Five Testing Stages 1 compile test.p4 p4 2 parse test.stf stf 17 

29 . Five Testing Stages 1 compile test.p4 p4 runtime source 2 parse test.stf stf input0.pcap expect0.pcap input1.pcap expect1.pcap …. …. 17