libink: a brokerless D-Bus implementation for Finit

Finit had no way to answer the question every service manager gets
asked: what is running, and change it.  D-Bus is how the rest of
userspace asks, but linking libdbus, sd-bus or GIO into PID 1 buys a
dependency, an allocator and a main loop we do not control.

So libink: the wire format, an object tree, and a bus of Finit's own
at /run/finit/bus, gated like INIT_SOCKET.  It speaks the standard
org.freedesktop.DBus, .Peer, .Introspectable interfaces, and Finit's
own Manager1, Service1 and Cond1 on top.  Methods that change
something are marked privileged and answered only for a caller the
kernel vouched for, via SO_PEERCRED.

Server and client both, since initctl is the first thing that needs
to talk to it, and its Start/Stop/Restart/Reload now go over the bus
rather than the legacy socket.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

libink/Makefile.am

@@ -0,0 +1,22 @@
+# libink — brokerless D-Bus library (server + client), born inside Finit
+lib_LTLIBRARIES          = libink.la
+libink_la_SOURCES        = server.c auth.c connection.c \
+                           proto.c proto.h               \
+                           marshal.c marshal.h           \
+                           dispatch.c builtin.c          \
+                           match.c                       \
+                           path.c                        \
+                           client.c io.c                 \
+                           internal.h
+
+libink_la_LDFLAGS        = -version-info 0:0:0
+libink_la_CPPFLAGS       = -D_GNU_SOURCE -D_DEFAULT_SOURCE -D_BSD_SOURCE
+libink_la_CFLAGS         = -W -Wall -Wextra -Wno-unused-parameter -std=gnu99
+
+# pkg-config support
+pkgconfigdir = $(libdir)/pkgconfig
+pkgconfig_DATA = libink.pc
+
+# Public headers install to $(includedir)/ink/
+inkdir = $(includedir)/ink
+ink_HEADERS = link.h path.h