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LPC2018 - P4C-XDP: Programming the Linux Kernel Forwarding Plane Using P4

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Published on Dec 3, 2018

url: https://linuxplumbersconf.org/event/2...
speaker: Fabian Ruffy (University of British Columbia), Mihai Budiu (VMware), William Tu (VMware)


The eXpress Data Path (XDP) is a new kernel-feature, intended to provide
fast packet processing as close as possible to device hardware. XDP
builds on top of the extended Berkely Packet Filter (eBPF) and allows
users to write a C-like packet processing program, which can be attached
to the device driver’s receiving queue. When the device observes an
incoming packet, the user-defined XDP program is triggered to execute on
the packet payload, making the decision as early as possible before
handing the packet down the processing pipeline.

P4 is a domain-specific language describing how packets are processed by
the data plane of a programmable network elements, including network
interface cards, appliances, and virtual switches. It provides an
abstraction that allows programmers to express existing and future
protocol format without coupling it to any data plane specific
knowledge. The language is explicitly designed to be protocol-agnostic.
A P4 programmer can write their own protocols and load the P4 program
into P4-capable network elements.
As high-level networking language, P4 supports a diverse set of compiler
backends and also possesses the capability to express eBPF and XDP programs.

We present P4C-XDP, a new backend for the P4 compiler. P4C-XDP leverages
XDP to aim for a high performance software data plane. The backend
generates a eBPF-compliant C representation from a given P4 program
which is passed to clang and llvm to produce the bytecode. Using
conventional eBPF kernel hooks the program can then be loaded into the
eBPF virtual machine in the device driver. The kernel verifier
guarantees the safety of the generated code. Any packets
received/transmitted from/to this device driver now trigger the
execution of the loaded P4 program.

The P4C-XDP project is an open source project hosted at
https://github.com/vmware/p4c-xdp/. We provide prove-of-concept sample
code under the tests directory, which contains a couple of examples such
as basic protocol parsing, checksum recalculation, multiple tables
lookups, and tunnel protocol en-/decapsulation.

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