android

android uevent如何触发

小樊
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2024-11-27 22:23:32
栏目: 编程语言

在Android系统中,uevent是Linux内核与用户空间进程之间进行通信的一种机制

  1. 创建一个内核模块(Kernel Module):

首先,你需要创建一个内核模块来发送uevent。以下是一个简单的内核模块示例:

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/uaccess.h>
#include <linux/device.h>
#include <linux/platform_device.h>
#include <linux/leds.h>

static int led_state = 0;

static int led_open(struct inode *inode, struct file *file) {
    printk(KERN_INFO "LED opened\n");
    return 0;
}

static int led_release(struct inode *inode, struct file *file) {
    printk(KERN_INFO "LED closed\n");
    return 0;
}

static ssize_t led_write(struct file *file, const char __user *ubuf, size_t count, loff_t *ppos) {
    char buf[32];
    if (copy_from_user(buf, ubuf, count)) {
        printk(KERN_ERR "Failed to copy data from user space\n");
        return -EFAULT;
    }

    if (strcmp(buf, "1") == 0) {
        led_state = 1;
        printk(KERN_INFO "LED turned on\n");
    } else if (strcmp(buf, "0") == 0) {
        led_state = 0;
        printk(KERN_INFO "LED turned off\n");
    } else {
        printk(KERN_ERR "Invalid input\n");
        return -EFAULT;
    }

    return count;
}

static const struct file_operations led_fops = {
    .open = led_open,
    .release = led_release,
    .write = led_write,
};

static int __init led_init(void) {
    int ret;
    struct device *dev;
    struct platform_device *pdev;

    pdev = platform_device_register_simple("led", -1, NULL);
    if (!pdev) {
        printk(KERN_ERR "Failed to register LED device\n");
        return -ENOMEM;
    }

    dev = pdev->dev;

    ret = device_create_file(dev, &dev_attr_led_state);
    if (ret) {
        printk(KERN_ERR "Failed to create LED device file\n");
        platform_device_unregister(pdev);
        return ret;
    }

    ret = sysfs_create_bin_file(&dev->kobj, &dev_attr_led_state);
    if (ret) {
        printk(KERN_ERR "Failed to create sysfs file for LED state\n");
        device_remove_file(dev, &dev_attr_led_state);
        platform_device_unregister(pdev);
        return ret;
    }

    printk(KERN_INFO "LED kernel module loaded\n");
    return 0;
}

static void __exit led_exit(void) {
    printk(KERN_INFO "LED kernel module unloaded\n");
    platform_device_unregister(pdev);
}

module_init(led_init);
module_exit(led_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Your Name");
MODULE_DESCRIPTION("A simple LED kernel module");
  1. 编译内核模块:

将上述代码保存为led_module.c,然后在终端中运行以下命令以编译内核模块:

make -C /path/to/your/kernel/source M=$(pwd) modules
  1. 加载内核模块:

将生成的.ko文件复制到Android设备的/data/local/tmp/目录下,然后使用adb命令加载模块:

adb push led_module.ko /data/local/tmp/
adb shell
su
cd /data/local/tmp/
insmod led_module.ko
  1. 触发uevent

在内核模块中,当LED状态发生变化时,会触发一个uevent。你可以通过写入/sys/class/gpio/gpioX/value(其中X是GPIO编号)来改变LED状态。例如,将LED打开:

echo 1 > /sys/class/gpio/gpioX/value

这将触发一个uevent,你可以在用户空间进程中监听这个事件。

  1. 监听uevent

在Android用户空间进程中,你可以使用BroadcastReceiver来监听uevent。首先,创建一个名为LedReceiver的类,继承自BroadcastReceiver

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.util.Log;

public class LedReceiver extends BroadcastReceiver {
    private static final String TAG = "LedReceiver";

    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (action.equals("com.example.LED_ACTION")) {
            Log.d(TAG, "LED state changed");
            // 处理LED状态变化的逻辑
        }
    }
}

然后,在AndroidManifest.xml中注册这个广播接收器:

<application
    ...
    <receiver android:name=".LedReceiver">
        <intent-filter>
            <action android:name="com.example.LED_ACTION" />
        </intent-filter>
    </receiver>
</application>

现在,当内核模块触发uevent时,LedReceiver将接收到这个事件并执行相应的逻辑。

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