Android系统APK操作GPIO读写及添加权限

需求描述

上层APK操作GPIO的diretction、value节点，实现点亮和熄灭灯，使用JNI方式，使用以下方式无效

extern "C"
JNIEXPORT jint JNICALL
Java_com_example_administrator_jni_Gpio_setOpenLed(JNIEnv *env, jclass instance) {
    int sd;
    system("echo 9 > /sys/class/gpio/export");
    system("echo out > /sys/class/gpio/gpio9/direction");
    system("echo 1 > /sys/class/gpio/gpio9/value");
    system("echo 9 > /sys/class/gpio/unexport");
    return 0;
}

实现方案

• GPIOControl.c：JNI调用接口

#include <jni.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>
#include <android/log.h>

#define TAG "jni_gpio"
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG,TAG ,__VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO,TAG ,__VA_ARGS__)
#define LOGW(...) __android_log_print(ANDROID_LOG_WARN,TAG ,__VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,TAG ,__VA_ARGS__)
#define LOGF(...) __android_log_print(ANDROID_LOG_FATAL,TAG ,__VA_ARGS__)

#define IN              0
#define OUT             1
#define LOW             0
#define HIGH            1

#define BUFFER_MAX    3
#define DIRECTION_MAX 48

/*
 * Class:     com_example_jnigpio_GPIOControl
 * Method:    exportGpio
 * Signature: (I)I
 */
JNIEXPORT jint JNICALL Java_com_example_jnigpio_GPIOControl_exportGpio(JNIEnv *env, jobject instance, jint gpio)
{
    char buffer[BUFFER_MAX];
    int len;
    int fd;

    fd = open("/sys/class/gpio/export", O_WRONLY);
    if (fd < 0) {
        LOGE("Failed to open export for writing!\n");
        return(0);
    }

    len = snprintf(buffer, BUFFER_MAX, "%d", gpio);
    if (write(fd, buffer, len) < 0) {
        LOGE("Fail to export gpio!\n");
        return 0;
    }

    close(fd);
    return 1;
}

/*
 * Class:     com_example_jnigpio_GPIOControl
 * Method:    setGpioDirection
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_example_jnigpio_GPIOControl_setGpioDirection(JNIEnv *env, jobject instance, jint gpio, jint direction)
{
    static const char dir_str[]  = "in\0out";
    char path[DIRECTION_MAX];
    int fd;

    snprintf(path, DIRECTION_MAX, "/sys/class/gpio/gpio%d/direction", gpio);
    fd = open(path, O_WRONLY);
    if (fd < 0) {
        LOGE("failed to open gpio direction for writing!\n");
        return 0;
    }

    if (write(fd, &dir_str[direction == IN ? 0 : 3], direction == IN ? 2 : 3) < 0) {
        LOGE("failed to set direction!\n");
        return 0;
    }

    close(fd);
    return 1;
}

/*
 * Class:     com_example_jnigpio_GPIOControl
 * Method:    readGpioStatus
 * Signature: (I)I
 */
JNIEXPORT jint JNICALL Java_com_example_jnigpio_GPIOControl_readGpioStatus(JNIEnv *env, jobject instance, jint gpio)
{
    char path[DIRECTION_MAX];
    char value_str[3];
    int fd;

    snprintf(path, DIRECTION_MAX, "/sys/class/gpio/gpio%d/value", gpio);
    fd = open(path, O_RDONLY);
    if (fd < 0) {
        LOGE("failed to open gpio value for reading!\n");
        return -1;
    }

    if (read(fd, value_str, 3) < 0) {
        LOGE("failed to read value!\n");
        return -1;
    }

    close(fd);
    return (atoi(value_str));
}

/*
 * Class:     com_example_jnigpio_GPIOControl
 * Method:    writeGpioStatus
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_example_jnigpio_GPIOControl_writeGpioStatus(JNIEnv *env, jobject instance, jint gpio, jint value)
{
    static const char values_str[] = "01";
    char path[DIRECTION_MAX];
    int fd;

    snprintf(path, DIRECTION_MAX, "/sys/class/gpio/gpio%d/value", gpio);
    fd = open(path, O_WRONLY);
    if (fd < 0) {
        LOGE("failed to open gpio value for writing!\n");
        return 0;
    }

    if (write(fd, &values_str[value == LOW ? 0 : 1], 1) < 0) {
        LOGE("failed to write value!\n");
        return 0;
    }

    close(fd);
    return 1;
}

/*
 * Class:     com_example_jnigpio_GPIOControl
 * Method:    unexportGpio
 * Signature: (I)I
 */
JNIEXPORT jint JNICALL Java_com_example_jnigpio_GPIOControl_unexportGpio(JNIEnv *env, jobject instance, jint gpio)
{
    char buffer[BUFFER_MAX];
    int len;
    int fd;

    fd = open("/sys/class/gpio/unexport", O_WRONLY);
    if (fd < 0) {
        LOGE("Failed to open unexport for writing!\n");
        return 0;
    }

    len = snprintf(buffer, BUFFER_MAX, "%d", gpio);
    if (write(fd, buffer, len) < 0) {
        LOGE("Fail to unexport gpio!");
        return 0;
    }

    close(fd);
    return 1;
}

• Android.mk：编译出libGPIOControl.so

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)
LOCAL_MODULE    := GPIOControl
LOCAL_SRC_FILES := GPIOControl.c
LOCAL_LDLIBS    := -llog

include $(BUILD_SHARED_LIBRARY)

• 添加节点读写权限

device/qcom/common/rootdir/etc/init.qcom.rc 

 on boot
+    chmod 0777 /sys/class/gpio/export
+    chmod 0777 /sys/class/gpio/unexport

• 添加实际节点的读写权限：ls -al sys/class/gpio/查看实际节点

device/qcom/common/rootdir/etc/ueventd.qcom.rc
 
+/sys/devices/soc/1000000.pinctrl/gpio/gpio* direction 0777 system system
+/sys/devices/soc/1000000.pinctrl/gpio/gpio* value 0777 system system

• 添加节点的SELinux权限

device/qcom/sepolicy/common/system_app.te

+allow system_app sysfs:file rw_file_perms;

• APK调用

1. Android应用修改AndroidManifest.xml文件，在manifest节点中添加android:sharedUserId="android.uid.system，修改Android.mk文件，添加LOCAL_CERTIFICATE := platform设置系统签名。
2. Android APK调用JNI加载so动态库：
   https://blog.csdn.net/weixin_44008788/article/details/114393087

相关拓展

• 节点读写

//读节点
private static String readSys(String path) {
    String prop = "waiting";// 默认值
    try {
        BufferedReader reader = new BufferedReader(new FileReader(path));
        prop = reader.readLine();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return prop;
}
//调用方法
 readSys("/sys/class/demo/version")

//写节点
private static String writeSys(String path) {
    try {
        BufferedWriter bufWriter = null;
        bufWriter = new BufferedWriter(new FileWriter(path));
        bufWriter.write("1");  // 写操作
        bufWriter.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}
//调用方法
writeSys("/sys/class/demo/version")

//以FileOutputStream写节点
void IOCtrl(int pin, int level) {
    String path;
    path = "/sys/class/gpio/gpio" + pin + "/value";
    try {
        FileOutputStream out = new FileOutputStream(path);
        out.write(level);
        out.flush();
        out.close();
    } catch (IOException e) {
        e.printStackTrace();
        return;
    }
}

• 添加设备文件节点权限

/sys/class/leds/green/brightness //快捷方式
/sys/devices/soc.0/gpio-leds.66/leds/green/brightness //实际节点

操作LED灯的设备文件节点为APP层system app进程开放该节点访问权限(读或写)，权限配置主要修改/device/qcom/sepolicy/common目录下的file.te、file_contexts和system_app.te三个文件

file.te修改如下

# GPIO accessed by system app
type sysfs_gpio, fs_type, sysfs_type;

file_contexts修改如下

/sys/devices/soc/1010000.pinctrl/gpio/gpio62/value           u:object_r:sysfs_gpio:s0
/sys/devices/soc/1010000.pinctrl/gpio/gpio63/value           u:object_r:sysfs_gpio:s0

system_app.te修改如下

allow system_app sysfs_gpio:file rw_file_perms;　　

如果通过以上添加SELinux之后，仍没有权限读写sys或proc节点，需要到init.rc里面配置如下

chown system system 文件结点
chmod 777 文件结点

相关参考

https://blog.csdn.net/wds1181977/article/details/54967110
https://blog.csdn.net/liangtianmeng/article/details/84698568
https://blog.csdn.net/d38825/article/details/81240851
https://blog.csdn.net/K_Hello/article/details/90038078
android 查看gpio状态_Android应用层操作GPIO
Android app如何正确读写系统sys设备节点