harmony 鸿蒙Driver Loading

2023-02-03
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Driver Loading

Overview

The HDF loads the drivers that match the configured device list.

Driver Loading Policies

The HDF supports on-demand loading and sequential loading of drivers. The preload field in the configuration file (see Driver Development) specifies the loading policy of a driver. The values are as follows:

typedef enum {
    DEVICE_PRELOAD_ENABLE = 0,
    DEVICE_PRELOAD_ENABLE_STEP2 = 1,
    DEVICE_PRELOAD_DISABLE = 2,
    DEVICE_PRELOAD_INVALID
} DevicePreload;

On-Demand Loading

The value 0 (DEVICE_PRELOAD_ENABLE) means to load the driver by default during the system boot process.
The value 1 (DEVICE_PRELOAD_ENABLE_STEP2) means to load the driver after a quick start is complete. If the system does not support quick start, the value 1 has the same meaning as DEVICE_PRELOAD_ENABLE.
The value 2 (DEVICE_PRELOAD_DISABLE) means to load the driver dynamically. When a user-mode process requests the driver service, the HDF attempts to dynamically load the driver if the driver service is not available. For more details, see Driver Messaging Mechanism.

Sequential Loading (Default)

The priority field (ranging from 0 to 200) in the configuration file determines the loading sequence of a host and a driver. For the drivers in different hosts, the drivers in the host with a smaller priority value are loaded first. For the drivers in the same host, the driver with a smaller priority value is loaded first.