8.2 Readiness

3 min read

"The network is up" means different things to different services, so netd reports a level, not a flag. Levels are ordered: absent < link < addressed < routed.

8.2.1 An interface's level #

From the kernel's state after the last reconcile:

A usable address is any IPv4 address other than a loopback one — a 169.254 link-local address counts, because it is the outcome of address acquisition — and any IPv6 address that is neither loopback nor link-local. Every up interface has an IPv6 link-local address, so counting one would make addressed mean nothing. Deprecated and tentative addresses count.

A default route is any route with prefix length 0, of either family, in the main table, out of the interface. It need not be one of netd's.

8.2.2 The machine's level #

The highest level among joined interfaces, or absent when none is joined. An IGNOREd or DOWN interface contributes nothing, whatever state it is in.

8.2.3 Publishing it #

At every publish (§2.2) netd computes the machine level. When it differs from the last one published — and at the first publish after startup, which precedes READY=1 — netd:

1. logs machine readiness is <level>;
2. sends the complete readiness set below in one datagram on the notify socket named by NOTIFY_SOCKET;
3. writes Readiness on Machine\System\Network.

The notify set is determined by the highest machine level:

Each value has its own LEVEL= line in the same datagram. The highest level comes last, so an older manager that retains only the last value continues to see the highest level. Upgrade peinit before or alongside netd to make every member available to dependents.

The set is sent only on a change. The notify channel is lossy by design and unacknowledged (PSPU §4.16), and a level is a statement of a current condition, so a lost one is corrected by the next change.

Each joined interface's own level is written as Status Readiness (§8.1).

8.2.4 What peinit makes of it #

peinit records the set netd last sent against the sending service, and resolves the network role to that service. A dependency on network:<level> waits until the service is active and its published set contains the requested level (peinit TRM §7.5).

A DHCPv4 lease that installs an address and default route in the same pass takes the highest machine level directly from link to routed. The notify datagram contains link, addressed and routed, so both network:addressed and network:routed dependents can start. peinit needs no knowledge of network level ordering; netd publishes every condition that holds. Losing the link replaces this set with absent, preventing new starts on any of the three previous conditions. Dependents already running keep running.

The registry, log and control status continue to report the highest machine level. net wait <level> polls over the control socket and succeeds when that level is at least the one named (§10.1).

Edit this page