1# uevent Customization
2
3## Overview
4
5### Introduction
6
7By default, OpenHarmony is designed to take an action based on the uevent received by the battery management system. To address your diverse demands, OpenHarmony provides the uevent customization function, allowing you to customize the uevents for taking desired actions. The customization is simply done through modification of the configuration file.
8
9## How to Develop
10
11### Setting Up the Environment
12
13**Hardware requirements:**
14
15Development board running the standard system, for example, the DAYU200 or Hi3516D V300 open source suite.
16
17**Environment requirements:**
18
19For details about the requirements on the Linux environment, see [Quick Start](../quick-start/quickstart-overview.md).
20
21### Getting Started with Development
22
23The following uses [DAYU200](https://gitee.com/openharmony/vendor_hihope/tree/master/rk3568) as an example to illustrate uevent customization.
24
251. Modify the `battery_config.json` file in the battery service configuration folder of the [HDI layer](https://gitee.com/openharmony/drivers_peripheral/tree/master/battery/interfaces/hdi_service/profile) and the [service layer](https://gitee.com/openharmony/powermgr_battery_manager/tree/master/services/native/profile). The uevent configuration is as follows:
26
27    ```json
28    {
29        "uevent": {
30            "SUBSYSTEM=hw_power": {
31                "BATTERY_UNDER_VOLTAGE=1": "shutdown",
32                "BATTERY_UNDER_CURRENT=2": "reboot",
33                "BATTERY_UNDER_VOLTAGE=3": "sendcommonevent"
34            }
35        }
36    }
37    ```
38
39    **Table 1** Subsystem configuration
40
41    | **Subsystem**| Description|
42    | -------- | -------- |
43    | SUBSYSTEM=hw_power | Subsystem: **hw_power**|
44
45    **Table 2** uevent description
46
47    | uevent| Description|
48    | -------- | -------- |
49    | BATTERY_UNDER_VOLTAGE=1 | uevent (regular expression supported) indicating that the battery voltage is less than 1.|
50    | BATTERY_UNDER_CURRENT=2 | uevent (regular expression supported) indicating that the battery voltage is less than 2.|
51    | BATTERY_UNDER_VOLTAGE=3 | uevent (regular expression supported) indicating that the battery voltage is less than 3.|
52
53    **Table 3** Action description
54
55    | Action| Type| Description|
56    | -------- | -------- | -------- |
57    | shutdown | string | Shut down the system.|
58    | reboot | string | Restart the system.|
59    | sendcommonevent | string | Send broadcast.|
60
612. Build the customized version by referring to [Quick Start](../quick-start/quickstart-overview.md).
62
63    ```shell
64    ./build.sh --product-name rk3568 --ccache
65    ```
66
673. Burn the customized version to the DAYU200 development board.
68
69### Debugging and Verification
70
711. Change the uevent receiving code (https://gitee.com/openharmony/drivers_peripheral/blob/master/battery/interfaces/hdi_service/src/battery_thread.cpp) to forcibly receive the uevent event BATTERY_UNDER_VOLTAGE=1 in the configuration file.
72   ```c++
73    void BatteryThread::UeventCallback(void* service)
74    {
75        char msg[UEVENT_MSG_LEN + UEVENT_RESERVED_SIZE] = { 0 };
76
77        ssize_t len = recv(ueventFd_, msg, UEVENT_MSG_LEN, 0);
78        if (len < 0 || len >= UEVENT_MSG_LEN) {
79            BATTERY_HILOGI(COMP_HDI, "recv return msg is invalid, len: %{public}zd", len);
80            return;
81        }
82
83        // msg separator
84        msg[len] = '\0';
85        msg[len + 1] = '\0';
86
87        std::string powerUevent;
88        if (!MatchPowerUevent(msg, powerUevent)) {
89            return;
90        }
91        powerUevent = "BATTERY_UNDER_VOLTAGE=1";
92        BATTERY_HILOGI(FEATURE_BATT_INFO, "PowerUevent msg:%{public}s",
93        powerUevent.c_str());
94        UpdateBatteryInfo(service, powerUevent);
95    }
96    ```
972. Build the customized version by referring to [Quick Start](../quick-start/quickstart-overview.md).
98
99    ```shell
100    ./build.sh --product-name rk3568 --ccache
101    ```
102
1033. Burn the customized version to the DAYU200 development board.
1044. Check whether the device is powered off when it receives a uevent indicating that the battery voltage is less than 1.
105
106## Reference
107During development, you can refer to the [default uevent configuration](https://gitee.com/openharmony/powermgr_battery_manager/tree/master/services/native/profile/), as shown below:
108
109The default configuration is as follows:
110
111```json
112{
113    "uevent": {
114        "SUBSYSTEM=hw_power": {
115            "BATTERY_UNDER_VOLTAGE=1": "shutdown",
116            "BATTERY_UNDER_VOLTAGE=2": "reboot",
117            "BATTERY_UNDER_VOLTAGE=3": "sendcommonevent"
118        }
119    }
120}
121```
122
123Packing path: /system/etc/battery
124