Joachim Wiberg
853e226812
A call is parked until the resolver says who sent it, and an outbound call sits in a pending slot until its reply lands. Neither had a way to give up. A broker that answers GetConnectionUnixUser slowly, or not at all, leaves the caller waiting forever and keeps the slot; four of those and every later privileged call is refused with LimitsExceeded until Finit restarts. libink cannot time itself out, it has no event loop, so the deadline is the embedder's to keep. One sweep per connection covers both, and the ordering between them stays in the library rather than in each embedder: calls first, because one timing out usually resolves the park it was made for, and AccessDenied tells that caller more than a bare timeout. The sweep is armed when a resolve is deferred and stops rearming as soon as nothing is outstanding, so a system that never meets a broker never wakes up for it. Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
libink — brokerless D-Bus for Finit
libink is a small C library implementing the D-Bus wire protocol,
both the server and the client side, without a broker and without any
dependency on libdbus, sd-bus, or GIO. It was born inside Finit to
let PID 1 be a bus of its own: clients connect straight to the listening
socket, authenticate with the standard SASL EXTERNAL handshake, and get
kernel-authenticated credentials via SO_PEERCRED.
For what the bus exposes and how to talk to it, see the User Guide, D-Bus Integration. This file covers the library itself.
Status
libink is an internal implementation detail of Finit: built as a libtool
convenience library, linked statically into finit and initctl,
nothing installed. There is deliberately no ABI promise yet — that
comes if/when libink is extracted into a project of its own. External
D-Bus clients need none of this; the wire protocol is the compatibility
surface, any standard D-Bus library works.
Layout
| File | Contents |
|---|---|
server.c |
Listening socket, accept, peer credential capture |
auth.c |
SASL EXTERNAL handshake, uid verification |
connection.c |
Per-peer state machine, message framing |
proto.c |
Wire header parse/build |
marshal.c |
Body (de)marshalling: basic types, arrays, variants |
dispatch.c |
Object tree, vtable registration, method dispatch |
builtin.c |
org.freedesktop.DBus.* stock interfaces |
match.c |
AddMatch/RemoveMatch rule parsing and signal filter |
path.c |
systemd-style _HH object path encoding |
client.c |
Outgoing connections, method calls, reply/signal wait |
io.c |
Shared EINTR-resilient read/write loops |
Public API symbols carry the link_* prefix (link.h), internal ones
__* (internal.h). Method handlers are registered as vtables of
link_method_t/link_property_t; the framework emits variant
signatures from the property table so the declared type is the single
source of truth.
The boundary to Finit is deliberate: nothing under libink/ includes a
Finit header. All glue lives in src/dbus.c — object registration,
signal emission from the service/condition/runlevel hook points, and
the uev event loop bridge. initctl uses the client half of the same
library, so one wire-format implementation serves both ends. If libink
is ever spun out, that file is the cut line.
Testing
The test/dbus-*.sh suite exercises the library end to end against a
live Finit in a namespace, driven by test/src/dbus-auth-client.c.
Wire-format conformance against third-party tools (dbus-send,
dbus-monitor) and fuzzing of the parsers are tracked as pre-merge
work — this is PID 1's attack surface.