[PATCH bpf-next v2 0/4] Add TC-BPF API

From: Kumar Kartikeya Dwivedi
Date: Mon Apr 19 2021 - 08:18:26 EST

This is the second version of the TC-BPF series.

It adds a simple API that uses netlink to attach the tc filter and its bpf
classifier. Currently, a user needs to shell out to the tc command line to be
able to create filters and attach SCHED_CLS programs as classifiers. With the
help of this API, it will be possible to use libbpf for doing all parts of bpf
program setup and attach.

Direct action is now the default, and currently no way to disable it has been
provided. This also means that SCHED_ACT programs are a lot less useful, so
support for them has been removed for now. In the future, if someone comes up
with a convincing use case where the direct action mode doesn't serve their
needs, a simple extension that allows disabling direct action mode and passing
the list of actions that would be bound to the classifier can be added.

In an effort to keep discussion focused, this series doesn't have the high level
TC-BPF API. It was clear that there is a need for a bpf_link API in the kernel,
hence that will be submitted as a separate patchset.

The individual commit messages contain more details, and also a brief summary of
the API.

v1 -> v2
v1: https://lore.kernel.org/bpf/20210325120020.236504-1-memxor@xxxxxxxxx

* netlink helpers have been renamed to object_action style.
* attach_id now only contains attributes that are not explicitly set. Only
the bare minimum info is kept in it.
* protocol is now an optional and defaults to ETH_P_ALL.
* direct-action mode is default, and cannot be unset for now.
* skip_sw and skip_hw options have also been removed.
* bpf_tc_cls_info struct now also returns the bpf program tag and id, as
available in the netlink response. This came up as a requirement during
discussion with people wanting to use this functionality.
* support for attaching SCHED_ACT programs has been dropped, as it isn't
useful without any support for binding loaded actions to a classifier.
* the distinction between dev and block API has been dropped, there is now
a single set of functions and user has to pass the special ifindex value
to indicate operation on a shared filter block on their own.
* The high level API returning a bpf_link is gone. This was already non-
functional for pinning and typical ownership semantics. Instead, a separate
patchset will be sent adding a bpf_link API for attaching SCHED_CLS progs to
the kernel, and its corresponding libbpf API.
* The clsact qdisc is now setup automatically in a best-effort fashion whenever
user passes in the clsact ingress or egress parent id. This is done with
exclusive mode, such that if an ingress or clsact qdisc is already set up,
we skip the setup and move on with filter creation.
* Other minor changes that came up during the course of discussion and rework.

Kumar Kartikeya Dwivedi (4):
tools: pkt_cls.h: sync with kernel sources
libbpf: add helpers for preparing netlink attributes
libbpf: add low level TC-BPF API
libbpf: add selftests for TC-BPF API

tools/include/uapi/linux/pkt_cls.h | 174 +++++++-
tools/lib/bpf/Makefile | 3 +
tools/lib/bpf/libbpf.h | 52 +++
tools/lib/bpf/libbpf.map | 5 +
tools/lib/bpf/netlink.c | 414 ++++++++++++++++--
tools/lib/bpf/nlattr.h | 48 ++
.../selftests/bpf/prog_tests/test_tc_bpf.c | 112 +++++
.../selftests/bpf/progs/test_tc_bpf_kern.c | 12 +
8 files changed, 789 insertions(+), 31 deletions(-)
create mode 100644 tools/testing/selftests/bpf/prog_tests/test_tc_bpf.c
create mode 100644 tools/testing/selftests/bpf/progs/test_tc_bpf_kern.c