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init: guarantee the ordering that actions are executed in

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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Also update some slightly out of date parts of the documentation: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
This commit is contained in:
Tom Cherry 2020-10-01 09:58:43 -07:00
parent 3e3e44c740
commit 34ee04762a
1 changed files with 20 additions and 24 deletions
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44
init/README.md
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@ -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
1. `/system/etc/init/hw/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
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
----------