init_lite

• Introduction
• Directory Structure
• Constraints
• Usage
• Repositories Involved

Introduction

The init_lite module starts system service processes from the time the kernel loads the first user-space process to the time the first application is started. In addition to loading key system processes, the module needs to configure their permissions during the startup and keep the specified process alive after sub-processes are started. If a process exits abnormally, the module needs to restart it, and to perform system reset for a special process.

Directory Structure

base/startup/init_lite/             # init_lite module
├── LICENSE
└── services
    ├── include                  # Header files for the init_lite module
    ├── src                      # Source files for the init_lite module
    └── test                     # Source files of the test cases for the init_lite module
        └── unittest
vendor
└──huawei
        └──camera
                └──init_configs  # init_lite configuration files (in JSON format, and deployed in /etc/init.cfg after image burning)

Constraints

Currently, the init_lite module applies only to small-system devices (reference memory ≥ 1 MB), for example, Hi3516D V300 and Hi3518E V300.

Usage

init divides the system startup into three phases:

pre-init: operations required before system services are started, for example, mounting a file system, creating a folder, and modifying permissions

init: operations required for starting system services.

post-init: operations required after system services are started.

In the init.cfg file, each of the preceding phases is represented by a job, which corresponds to a command set. The init_lite module initializes the system by executing the commands in each job in sequence. Jobs are executed in the following sequence: pre-init > init > post-init. All jobs are stored in the jobs array in the init.cfg file.

In addition to the jobs array, the init.cfg file also provides a services array, which is used to store the names, executable file paths, permissions, and other attribute information of the key system services that need to be started by the init process.

The file is stored in /vendor/hisilicon/hispark_aries/init_configs/ under /etc/. It is in JSON format, and its size cannot exceed 100 KB.

The format and content of the init.cfg file are as follows:

{
    "jobs" : [{
            "name" : "pre-init",
            "cmds" : [
                "mkdir /testdir",
                "chmod 0700 /testdir",
                "chown 99 99 /testdir",
                "mkdir /testdir2",
                "mount vfat /dev/mmcblk0p0 /testdir2 noexec nosuid"
            ]
        }, {
            "name" : "init",
            "cmds" : [
                "start service1",
                "start service2"
             ]
        }, {
             "name" : "post-init",
             "cmds" : []
        }
    ],
    "services" : [{
            "name" : "service1",
            "path" : "/bin/process1",
            "uid" : 1,
            "gid" : 1,
            "secon" : "u:r:untrusted_app:s0",
            "once" : 0,
            "importance" : 1,
            "caps" : [0, 1, 2, 5]
    }, {
            "name" : "service2",
            "path" : "/bin/process2",
            "uid" : 2,
            "gid" : 2,
            "secon" : "u:r:untrusted_app:s0",
            "once" : 1,
            "importance" : 0,
            "caps" : []
        }
    ]
}

Table 1 Job description

Job Name	Description
pre-init	Job that is executed first. Operations (for example, creating a folder) required before the process startup are executed in this job.
init	Job that is executed in between. Operations (for example, service startup) are executed in this job.
post-init	Job that is finally executed. Operations (for example, mounting the device after the driver initialization) required after the process startup are executed in this job.

A single job can hold a maximum of 30 commands (only start, mkdir, chmod, chown, mount, and loadcfg are supported currently). The command name and parameters (128 bytes or less) must be separated by only one space.

Table 2 Commands supported by a job

Command	Format and Example	Description
mkdir	mkdir target folder Example: mkdir /storage/myDirectory	Creates a folder. mkdir and the target folder must be separated by only one space.
chmod	chmod permission target Examples: chmod 0600 /storage/myFile.txt chmod 0750 /storage/myDir	Modifies the permission, which must be in the 0xxx format. chmod, permission, and target must be separated by only one space.
chown	chown uid gid target Example: chown 900 800 /storage/myDir chown 100 100 /storage/myFile.txt	Modifies the owner group. chown, uid, gid, and target must be separated by only one space.
mount	mount fileSystemType src dst flags data Example: mount vfat /dev/mmcblk0 /sdc rw,umask=000 mount jffs2 /dev/mtdblock3 /storage nosuid	Mounts devices. Every two parameters must be separated by only one space. Currently, supported flags include nodev, noexec, nosuid, rdonly, and optionally data.
start	start serviceName Example: start foundation start shell	Starts services. serviceName must be contained in the services array.
loadcfg	loadcfg filePath Example: loadcfg /patch/fstab.cfg	Loads other .cfg files. The maximum size of the target file (only /patch/fstab.cfg supported currently) is 50 KB. Each line in the /patch/fstab.cfg file is a command. The command types and formats must comply with their respective requirements mentioned in this table. A maximum of 20 commands are allowed.

Table 3 Elements in the services array

Field	Description
name	Name of the current service. The value cannot be empty and can contain a maximum of 32 bytes.
path	Full path (including parameters) of the executable file for the current service. This is an array. Ensure that the first element is the path of the executable file, the maximum number of elements is 20, and each element is a string that contains a maximum of 64 bytes.
uid	User ID (UID) of the current service process.
gid	Group ID (GID) of the current service process.
secon	Security context of the current service process (no need to set currently).
once	Whether the current service process is a one-off process. 1: The current service process is a one-off process. If the process exits, the init process does not restart it. 0: The current service process is not a one-off process. If the process exits, the init process restarts it upon receiving the SIGCHLD signal. Note: If a non-one-off process exits for five consecutive times within four minutes, the init process will no longer restart it at the fifth exit.
importance	Whether the current service process is a key system process. 0: The current service process is not a key system process. If it exits, the init process does not reset or restart the system. 1: The current service process is a key system process. If it exits, the init process resets and restarts the system.
caps	Capabilities required by the current service. They are evaluated based on the capabilities supported by the security subsystem and configured in accordance with the principle of least permission. Currently, a maximum of 100 values can be configured.

Repositories Involved

Startup subsystem

startup_syspara_lite

startup_appspawn_lite

startup_bootstrap_lite

startup_init_lite