Overview

Copy Markdown View Source

Linx.Netlink is Elixir's voice on the kernel's AF_NETLINK bus — the socket through which userspace asks the kernel to do things and report state, with the wire format encoded and decoded in pure Elixir.

Netlink is the kernel's structured request/reply (and broadcast) channel for a whole family of subsystems: the networking stack via rtnetlink, the firewall via nfnetlink, and — through generic netlink — WireGuard, nl80211 and more. Each message is an nlmsghdr envelope wrapping type-length-value attributes. Linx.Netlink speaks that protocol directly: a small layered codec (Socket → Message/Attr → Request), family-agnostic at the bottom, with each protocol family — Rtnl for networking, Nfnl for netfilter — built on top. A single tiny NIF handles the one thing the BEAM cannot do safely itself: entering another network namespace to bind the socket there.

Where it fits

Netlink is how the other subsystems reach into the kernel's networking world. While a child is parked at the Linx.Process checkpoint, Linx.Netlink.Rtnl moves an interface into its netns and assigns addresses and routes — so the workload's first instruction already sees a configured network. It is also the transport Linx.Netfilter rides on (via Linx.Netlink.Nfnl). The wire layers are shared and family-agnostic; consumers are container engines and network orchestrators that sequence rtnl calls around the checkpoint, plus anything that just wants to inspect or configure host networking.

Flow

A socket is bound in a chosen namespace — the host, or a child's netns by pid — and every request it sends, and reply it collects, lands in that namespace's networking stack.

flowchart LR
    caller["Rtnl.Link.list / Address.add / …"] --> req["Request<br/>(send + collect reply)"]
    req --> sock["Socket<br/>bound to a netns"]
    subgraph host["host netns"]
        khost["kernel networking stack"]
    end
    subgraph child["child netns — {:pid, n}"]
        kchild["kernel networking stack"]
    end
    sock -->|":host"| khost
    sock -->|"{:pid, n} (setns via NIF)"| kchild
    khost -->|"nlmsg reply / multipart dump"| req
    kchild -->|"nlmsg reply / multipart dump"| req

Learn more