NervesUEvent (nerves_uevent v0.1.4)

NervesUEvent listens for events from the Linux kernel, automatically loads device drivers, and forwards them to your Elixir programs.

NervesUEvent is a very simple version of the Linux udevd. Just like udevd does for desktop Linux, NervesUEvent registers to receive UEvents from the Linux kernel. Unlike udevd, NervesUEvent only runs modprobe when needed and keeps track of what hardware is in the system. For most Nerves use cases, udevd isn't needed.

Summary

Functions

get(property, default \\ nil)

Get the most recent value of UEvent report

get_all()

Get all reported UEvents

match(pattern)

Run an arbitrary match against UEvents

stats()

Return counters collected by the uevent port.

subscribe(property)

Subscribe to uevent notifications

Functions

get(property, default \\ nil)

@spec get(PropertyTable.property(), PropertyTable.value()) :: PropertyTable.value()

Get the most recent value of UEvent report

For example,

> NervesUEvent.get(["devices", "platform", "leds", "leds", "red:indicator-1"])
%{
  "of_compatible_n" => "0",
  "of_fullname" => "/leds/rgb1-blue",
  "of_name" => "rgb1-blue",
  "subsystem" => "leds"
}}

get_all()

@spec get_all() :: [{PropertyTable.property(), PropertyTable.value()}]

Get all reported UEvents

match(pattern)

@spec match(PropertyTable.pattern()) :: [
  {PropertyTable.property(), PropertyTable.value()}
]

Run an arbitrary match against UEvents

Use :_ in the path to accept any value in that position Use :"$" at the end of the path to perform an exact match

stats()

@spec stats() :: NervesUEvent.UEvent.stats()

Return counters collected by the uevent port.

Top-level keys:

:uevents_received — netlink messages successfully read
:uevents_dropped — ENOBUFS incidents (kernel dropped one or more messages)
:modprobes_called — modprobe child processes launched
:modaliases_queued — modaliases queued for modprobe
:modaliases_dropped — modaliases dropped because the queue was full while a modprobe was already in flight
:modprobe_fork_failures — fork() failures when launching modprobe
:peak_queue_n — high-water mark for queued modalias count
:peak_queue_bytes — high-water mark for the modalias byte buffer
:actions — nested map of add | change | remove | move | bind | unbind | other counts, matching the uevent ACTION field

Counters are cumulative since the port started and updated after 5 seconds of inactivity. Values will lag bursts especially at boot.