Override or disable nerves runtime init

README.md

@@ -71,6 +71,21 @@ the application partition. The following variables are important:
 * `[partition].nerves_fw_application_part0_target` - where the partition should
   be mounted (e.g. `/root` or `/mnt/appdata`)
 
+This default behavior is handled by `Nerves.Runtime.Init`. To override it with your
+own you can configure a different module that is a GenServer with no options:
+
+```elixir
+config :nerves_runtime,
+  init_module: MyApp.FilesystemInit
+```
+
+Or you can disable it:
+
+```elixir
+config :nerves_runtime,
+  init_module: nil
+```
+
 ## Nerves System and Firmware Metadata
 
 All official Nerves systems maintain a list of key-value pairs for tracking
@@ -357,4 +372,3 @@ All original source code in this project is licensed under Apache-2.0.
 
 Additionally, this project follows the [REUSE recommendations](https://reuse.software)
 and labels so that licensing and copyright are clear at the file level.
-

lib/nerves_runtime/application.ex

@@ -20,21 +20,29 @@ defmodule Nerves.Runtime.Application do
     load_services()
 
     options = Application.get_all_env(:nerves_runtime)
-    children = [{FwupOps, options}, {KV, options} | target_children()]
+    init_module = Keyword.get(options, :init_module, Nerves.Runtime.Init)
+    children = [{FwupOps, options}, {KV, options} | target_children(init_module)]
 
     opts = [strategy: :one_for_one, name: Nerves.Runtime.Supervisor]
     Supervisor.start_link(children, opts)
   end
 
   if Mix.target() == :host do
-    defp target_children(), do: []
+    defp target_children(_), do: []
     defp load_services(), do: :ok
   else
-    defp target_children() do
+    defp target_children(nil) do
+      [
+        NervesLogging.KmsgTailer,
+        NervesLogging.SyslogTailer
+      ]
+    end
+
+    defp target_children(init_module) do
       [
         NervesLogging.KmsgTailer,
         NervesLogging.SyslogTailer,
-        Nerves.Runtime.Init
+        init_module
       ]
     end
 

lib/nerves_runtime/init.ex

@@ -29,6 +29,18 @@ defmodule Nerves.Runtime.Init do
   have also had stalls when formatting while waiting for enough entropy to
   generate a UUID. Look into hardcoding UUIDs or enabling a hw random number
   generator to increase entropy.
+
+  This GenServer is started by default. It can be prevented or overriden by
+  setting the config option `:init_module` to another module or `nil`. This
+  allows customizing application filesystem initialization:
+
+  ```elixir
+  # Override with GenServer module
+  config :nerves_runtime, init_module: MyApp.FilesystemInit
+  # Disable
+  config :nerves_runtime, init_module: nil
+  ```
+
   """
   use GenServer