[Oisf-devel] Best userspace programming API for XDP features query to kernel?

Jesper Dangaard Brouer brouer at redhat.com
Wed Apr 4 12:28:56 UTC 2018

Hi Suricata people,

When Eric Leblond (and I helped) integrated XDP in Suricata, we ran
into the issue, that at Suricata load/start time, we cannot determine
if the chosen XDP config options, like xdp-cpu-redirect[1], is valid on
this HW (e.g require driver XDP_REDIRECT support and bpf cpumap).

We would have liked a way to report that suricata.yaml config was
invalid for this hardware/setup.  Now, it just loads, and packets gets
silently dropped by XDP (well a WARN_ONCE and catchable via tracepoints).

My question to suricata developers: (Q1) Do you already have code that
query the kernel or drivers for features?

At the IOvisor call (2 weeks ago), we discussed two options of exposing
XDP features avail in a given driver.

Option#1: Extend existing ethtool -k/-K "offload and other features"
with some XDP features, that userspace can query. (Do you already query
offloads, regarding Q1)

Option#2: Invent a new 'ip link set xdp' netlink msg with a query option.

(Q2) Do Suricata devs have any preference (or other options/ideas) for
the way the kernel expose this info to userspace?

[1] http://suricata.readthedocs.io/en/latest/capture-hardware/ebpf-xdp.html#the-xdp-cpu-redirect-case
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

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