xdp-project-bpf-examples/pping/TODO.md

# TODO

## Protocols
- [x] TCP (based on timestamp options)
  - [x] Skip pure ACKs for egress
    - Timestamping pure ACKs may lead to erroneous RTTs (ex. delay
      between application attempting to send data being recognized as
      an RTT)
  - [ ] Add fallback to SEQ/ACK in case of no timestamp?
    - Some machines may not use TCP timestamps (either not supported
      at all, or disabled as in ex. Windows 10)
    - If one only considers SEQ/ACK (and don't check for SACK
      options), could result in ex. delay from retransmission being
      included in RTT
- [ ] ICMP (ex Echo/Reply)
- [ ] QUIC (based on spinbit)

## General pping
- [x] Add sampling so that RTT is not calculated for every packet
      (with unique value) for large flows
  - [ ] Allow short bursts to bypass sampling in order to handle 
        delayed ACKs
- [x] Keep some per-flow state
  - Will likely be needed for the sampling
  - [ ] Could potentially include keeping track of average RTT, which
        may be useful for some decisions (ex. how often to sample,
        when entry can be removed etc)
  - [x] Could potentially include keeping track of minimum RTT (as
        done by the original pping), ex. to track bufferbloat
  - [ ] Could potentially include keeping track of if flow is
        bi-directional
    - Original pping checks if flow is bi-directional before adding
      timestamps, but this could miss shorter flows
- [ ] Dynamically grow the maps if they are starting to get full
- [ ] Improve map cleaning: Use a dynamic time to live for map entries
      based on flow's RTT, instead of static 10s limit
  - Keeping entries around for a long time allows the map to grow
    unnecessarily large, which slows down the cleaning and may block
    new entries
- [ ] Use libxdp to load XDP program
- [ ] Add support for other hooks
  - Ex TC-BFP on ingress instead of XDP?

## Done
- [x] Clean up commits and add signed-off-by tags
- [x] Add SPDX-license-identifier tags
- [x] Format C-code in kernel style
- [x] Use existing functionality to reuse maps by using BTF-defined
      maps
  - [x] Use BTF-defined maps for TC-BPF as well if iproute has libbpf
        support
- [x] Cleanup: Unload TC-BPF at program shutdown, and unpin map - In
      userspace part
- [x] Add IPv6 support
- [x] Refactor to support easy addition of other protocols
- [x] Load tc-bpf program with libbpf (only attach it with tc)
- [x] Switch to libbpf TC-BPF API for attaching the TC-BPF program
- [x] Add option for machine-readable output (as original pping)
  - It may be a good idea to keep the same format as original pping,
    so that tools such as [ppviz](https://github.com/pollere/ppviz)
    works for both pping implementations.
- [x] Add timestamps to output (as original pping)