Android init language用于init解析init.rc等初始化文件时使用
官方的解释文档详见system/core/init/readme.txt
关于Init language的解析的代码分析可参见http://blog.csdn.net/orz415678659/article/details/8769814
init lang基本上由四个Statements：Actions，Commands，Services和Options，下面分别介绍：
- 每一个语句占据一行，并且各个关键字被空格分开。c规范中的（如 \n）反斜杠将被忽略(backslash escapes)而被认为是一个空格 ，双引号用来保证空格不会把一个文字串分分为多个关键字。行最后的反斜杠用作续行。
- 由 # （前面允许有空格）开始的行都是注释行(comment)
- 一个actions 或 services 的开始隐含声明了一个新的段，所有commands 或 options 属于最近的声明。在第一个段之前的 commands 或 options 都会被忽略
- 每一个actions 和 services 都有不同的名字。后面与前面发生重名的，那么这个后面重名的将被忽略或被认为是一个错误
Actions和Services会建立一个section，command和options是Section的修饰
一、Action的格式是
on <trigger>
<command>
<command>
<command>
1）trigger
trgger的定义是Triggers are strings used to match certain kinds of events that cause an action to occur.
本意是某件事情发生时，比如boot，就执行相应的command，但实际上只是把相关阶段的命令集合放在一起执行，并控制
命令集合的执行顺序。实际使用中的trigger可以根据需要自由定义，只要相应的Init程序中添加相应trigger处理(action_for_each_trigger)
即可，常见的trigger有：early-init,
init,early-fs,fs,post-fs,post-fs-data,early-boot,boot
| Trigger | Description |
|---|---|
boot |
This is the first trigger that occurs when init starts (after /init.conf is loaded). |
<name>=<value> |
Triggers of this form occur when the property <name> is set to the specific value <value>. |
device-added-<path> |
Triggers of these forms occur when a device node is added or removed. |
service-exited-<name> |
Triggers of this form occur when the specified service exits. |
2）Command
command就是在action或section中执行的命令，可以定义多个command
chmod <octal-mode> <path> Change file access permissions.
chown <owner> <group> <path>
Change file owner and group.
chown <owner> <group> <path>
Change file owner and group.
chroot <directory>
Change process root directory.
| Command | Description |
|---|---|
exec <path> [ <argument> ]* |
Fork and execute a program (<path>). This will block until the program completes execution. Try to avoid exec. Unlike the builtin commands, it runs the risk of getting init "stuck". |
export <name> <value> |
Set the environment variable <name> equal to <value> in the global environment (which will be inherited by all processes started after this command is executed). |
ifup <interface> |
Bring the network interface <interface> online. |
import <filename> |
Parse an init config file, extending the current configuration. |
hostname <name> |
Set the host name. |
class_start <serviceclass> |
Start all services of the specified class if they are not already running. |
class_stop <serviceclass> |
Stop all services of the specified class if they are currently running. |
domainname <name> |
Set the domain name. |
insmod <path> |
Install the module at <path>. |
mkdir <path> |
Make a directory at <path>. |
mount <type> <device> <dir> [ <mountoption> ]* |
Attempt to mount the named device at the directory <dir> <device>. This may be of the form mtd@name to specify a mtd block device by name. |
setkey |
- currenlty undefined - |
setprop <name> <value> |
Set system property <name> to <value>. |
setrlimit <resource> <cur> <max> |
Set the rlimit for a resource. |
start <service> |
Start a service running if it is not already running. |
stop <service> |
Stop a service from running if it is currently running. |
symlink <target> <path> |
Create a symbolic link at <path> with the value <target>. |
write <path> <string> [ <string> ]* |
Open the file at <path> and write one or more strings to it with write(2). |
二、Services的格式是
service <name> <pathname> [ <argument> ]*
<option>
<option>
...
1）option
onrestart Execute a Command (see below) when service restarts.
critical This is a device-critical service. If it exits more than four times in four minutes, the device will reboot into recovery mode.
console 指定console时使用，例如：
service console /system/bin/sh
class core
console
disabled
user shell
group log
| Option | Description |
|---|---|
disabled |
This service will not automatically start with its class. It must be explicitly started by name. |
socket <type> <name> <perm> [ <user> [ <group> ] ] |
Create a unix domain socket named values include |
user <username> |
Change to username before exec'ing this service. Currently defaults to root. |
group <groupname> [ <groupname> ]* |
Change to groupname before exec'ing this service. Additional groupnames beyond the first, which is required, are used to set additional groups of the process (with setgroups()). Currently defaults to root. |
capability [ <capability> ]+ |
Set linux capability before exec'ing this service |
oneshot |
Do not restart the service when it exits. |
class <name> |
Specify a class name for the service. All services in a named class must start and stop together. A service is considered of class "default" if one is not specified via the class option. |