examples: add floodguard (adaptive in-kernel blackholing) - #619
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This was referenced Jul 4, 2026
A demoable dataplane use case: a softirq PRE_ROUTING netfilter hook counts packets per source address and, once a source crosses a threshold, drops its traffic and broadcasts the mitigation on a netlink.channel for a userspace dashboard. Detection, mitigation and telemetry all run in the kernel, in Lua, hot-loaded, with no userspace agent in the packet path. Third of three use-case PRs toward the Netdev talk. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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A demoable dataplane use case for the netlink support: adaptive blackholing that detects flooding sources and mitigates them entirely in the kernel, in Lua, in softirq, streaming each action to userspace over a netlink channel.
A
PRE_ROUTINGnetfilter hook counts packets per source address in anrcu.table; once a source crossesTHRESHOLDpackets it is dropped and ablackholed <ip>event is broadcast on thefloodguardnetlink.channel. Detection, mitigation and telemetry all run in one softirq runtime, hot-loaded, with no userspace agent in the packet path. The channel is a genl multicast family a userspace dashboard subscribes to (template:tests/netlink/channel_subscriber.c).Validated end-to-end against a network namespace source: 150 pings from
10.99.0.2past a threshold of 100 → ~99 get through, the rest are dropped, and dmesg shows the blackhole event with the correct source address. Run steps in the README.Scope note
This showcases the softirq
netlink.channel(kernel-to-userspace telemetry) with dataplane mitigation. The control-plane variant — a sleepable reactor installing a blackhole FIB rule vianetlink.rt— is a natural follow-up once rule support (#616) and anFRA_SRCselector land; it is deliberately not stacked here so this PR stays self-contained onmaster.Third of three use-case PRs toward the Netdev talk (nl80211 #617, netfailover #618, floodguard).
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