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Use global functions to make use of function-by-function verification. This allows the verifier to analyze parts of the program individually from each other, which should help reduce the verification complexity (the number of instructions the verifier must go through to verify the program) and help prevent exponentially growing with every loop or branch added to the code. In this case, break out the packet parsing (parse_packet_identifier) as a global function, so that it can be handled separately from the logic after it (updating flow state, saving timestamps, matching replies to timestamps, calculating and pushing RTTs) etc. To do this, create small separate wrapper functions (parse_packet_identifier_tc() and parse_packet_identifier_xdp()) for tc/xdp, so that the verifier can correctly identify the arguments as pointers to context (PTR_TO_CTX) when evaluating the global functions. Also create small wrapper functions pping_tc() and pping_xdp() which call the corresponding parse_packet_identifier_tc/xdp function. For this to work in XDP mode (which is the default), the kernel must have been patched with a fix that addresses an issue with how global functions are verified for XDP programs, see: https://lore.kernel.org/all/20220606075253.28422-1-toke@redhat.com/ Signed-off-by: Simon Sundberg <simon.sundberg@kau.se>
Practical BPF examples
This git repository contains a diverse set of practical BPF examples that solve (or demonstrate) a specific use-case using BPF.
It is meant to ease doing rapid prototyping and development, writing C-code BPF programs using libbpf. The goal is to make it easier for developers to get started coding.
Many developers struggle to get a working BPF build environment. The repo enviroment makes it easy to build/compile BPF programs by doing the necessary libbpf setup transparently and detect missing compile dependencies (via the configure script). It is a declared goal to make BPF programming more consumable by detecting and reporting issues (when possible).