Re: [PATCH bpf-next v3 2/3] libbpf: add low level TC-BPF API

On 4/21/21 9:48 PM, Toke Høiland-Jørgensen wrote:

Andrii Nakryiko [off-list ref] writes:

quoted

On Tue, Apr 20, 2021 at 12:37 PM Kumar Kartikeya Dwivedi
[off-list ref] wrote:

[...]

quoted

quoted

---
  tools/lib/bpf/libbpf.h   |  44 ++++++
  tools/lib/bpf/libbpf.map |   3 +
  tools/lib/bpf/netlink.c  | 319 ++++++++++++++++++++++++++++++++++++++-
  3 files changed, 360 insertions(+), 6 deletions(-)

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index bec4e6a6e31d..b4ed6a41ea70 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h

@@ -16,6 +16,8 @@
  #include <stdbool.h>
  #include <sys/types.h>  // for size_t
  #include <linux/bpf.h>
+#include <linux/pkt_sched.h>
+#include <linux/tc_act/tc_bpf.h>

apart from those unused macros below, are these needed in public API header?

quoted

  #include "libbpf_common.h"

@@ -775,6 +777,48 @@ LIBBPF_API int bpf_linker__add_file(struct bpf_linker *linker, const char *filen
  LIBBPF_API int bpf_linker__finalize(struct bpf_linker *linker);
  LIBBPF_API void bpf_linker__free(struct bpf_linker *linker);

+/* Convenience macros for the clsact attach hooks */
+#define BPF_TC_CLSACT_INGRESS TC_H_MAKE(TC_H_CLSACT, TC_H_MIN_INGRESS)
+#define BPF_TC_CLSACT_EGRESS TC_H_MAKE(TC_H_CLSACT, TC_H_MIN_EGRESS)

these seem to be used only internally, why exposing them in public
API?

No they're "aliases" for when you want to attach the filter directly to
the interface (and thus install the clsact qdisc as the root). You can
also use the filter with an existing qdisc (most commonly HTB), in which
case you need to specify the qdisc handle as the root. We have a few
examples of this use case:

https://github.com/xdp-project/bpf-examples/tree/master/traffic-pacing-edt
and
https://github.com/xdp-project/xdp-cpumap-tc

I'm a bit puzzled, could you elaborate on your use case on why you wouldn't
use the tc egress hook for those especially given it's guaranteed to run
outside of root qdisc lock?

Some pointers as well:

  - http://vger.kernel.org/lpc-bpf2018.html#session-1
  - https://netdevconf.info/0x14/session.html?talk-replacing-HTB-with-EDT-and-BPF
  - https://cilium.io/blog/2020/11/10/cilium-19#bwmanager

Thanks,
Daniel