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Commit 34ee0476 authored by Tom Cherry's avatar Tom Cherry
Browse files

init: guarantee the ordering that actions are executed in 

The README.md states that this ordering is not guaranteed to give
flexibility for the future, however it's time to state that this
ordering is guaranteed, especially since:

1) We have a tests, EventTriggerOrder and
   EventTriggerOrderMultipleFiles, which have guaranteed this ordering
   since 2017.
2) We have users requesting and depending on this order

Also update some slightly out of date parts of the documentation:
1) We import /system/etc/init/hw/init.rc instead of /init.rc as the
   first import
2) We additionally import /system_ext/etc/init and /product/etc/init

Test: n/a
Change-Id: I6d7b8d9e52f0d52bee320d5074ebb74a537f9150
parent 3e3e44c7

init/README.md

+20 −24
Original line number Diff line number Diff line
@@ -31,14 +31,13 @@ The init language is used in plain text files that take the .rc file 
extension.  There are typically multiple of these in multiple

locations on the system, described below.



/init.rc is the primary .rc file and is loaded by the init executable

at the beginning of its execution.  It is responsible for the initial

set up of the system.

`/system/etc/init/hw/init.rc` is the primary .rc file and is loaded by the init executable at the

beginning of its execution.  It is responsible for the initial set up of the system.



Init loads all of the files contained within the

/{system,vendor,odm}/etc/init/ directories immediately after loading

the primary /init.rc.  This is explained in more details in the

Imports section of this file.

`/{system,system_ext,vendor,odm,product}/etc/init/` directories immediately after loading

the primary `/system/etc/init/hw/init.rc`.  This is explained in more details in the

[Imports](#imports) section of this file.



Legacy devices without the first stage mount mechanism previously were

able to import init scripts during mount_all, however that is deprecated
@@ -689,29 +688,22 @@ imports are handled as a file is being parsed and follow the below logic. 


There are only three times where the init executable imports .rc files:



   1. When it imports /init.rc or the script indicated by the property

   1. When it imports `/system/etc/init/hw/init.rc` or the script indicated by the property

      `ro.boot.init_rc` during initial boot.

   2. When it imports /{system,vendor,odm}/etc/init/ for first stage mount

      devices immediately after importing /init.rc.

   2. When it imports `/{system,system_ext,vendor,odm,product}/etc/init/` immediately after

      importing `/system/etc/init/hw/init.rc`.

   3. (Deprecated) When it imports /{system,vendor,odm}/etc/init/ or .rc files

      at specified paths during mount_all, not allowed for devices launching

      after Q.



The order that files are imported is a bit complex for legacy reasons

and to keep backwards compatibility.  It is not strictly guaranteed.

The order that files are imported is a bit complex for legacy reasons.  The below is guaranteed:



The only correct way to guarantee that a command has been run before a

different command is to either 1) place it in an Action with an

earlier executed trigger, or 2) place it in an Action with the same

trigger within the same file at an earlier line.



Nonetheless, the de facto order for first stage mount devices is:

1. /init.rc is parsed then recursively each of its imports are

   parsed.

2. The contents of /system/etc/init/ are alphabetized and parsed

   sequentially, with imports happening recursively after each file is

1. `/system/etc/init/hw/init.rc` is parsed then recursively each of its imports are

   parsed.

3. Step 2 is repeated for /vendor/etc/init then /odm/etc/init

2. The contents of `/system/etc/init/` are alphabetized and parsed sequentially, with imports

   happening recursively after each file is parsed.

3. Step 2 is repeated for `/system_ext/etc/init`, `/vendor/etc/init`, `/odm/etc/init`,

   `/product/etc/init`



The below pseudocode may explain this more clearly:
@@ -720,13 +712,17 @@ The below pseudocode may explain this more clearly: 
      for (import : file.imports)

        Import(import)



    Import(/init.rc)

    Directories = [/system/etc/init, /vendor/etc/init, /odm/etc/init]

    Import(/system/etc/init/hw/init.rc)

    Directories = [/system/etc/init, /system_ext/etc/init, /vendor/etc/init, /odm/etc/init, /product/etc/init]

    for (directory : Directories)

      files = <Alphabetical order of directory's contents>

      for (file : files)

        Import(file)



Actions are executed in the order that they are parsed.  For example the `post-fs-data` action(s)

in `/system/etc/init/hw/init.rc` are always the first `post-fs-data` action(s) to be executed in

order of how they appear in that file.  Then the `post-fs-data` actions of the imports of

`/system/etc/init/hw/init.rc` in the order that they're imported, etc.



Properties

----------