Bad type conversion in android ndk

Question

I want my Android application to create a fake virtual device, to achieve this the device needs to be rooted and uinput module is needed.

I am using the following code to create the device, calling

static{ System.loadLibrary("myModule"); }
CreateVirtualDevice("Devname",0x123,0x123);

inside my java code. Here the native code:

#include <string.h>
#include <jni.h>
#include <fcntl.h>

#include <linux/input.h>
#include <linux/uinput.h>

static int fd;
static struct uinput_user_dev dev;

short int analog_axis_list[] = { ABS_X,ABS_Y,ABS_RX,ABS_RY, -1};

jint Java_com_example_app_MyClass_CreateVirtualDevice(
        JNIEnv* env, jobject thiz, jstring param, jint param2, jint param3) {

    int i;

    memset(&dev, 0, sizeof(dev));
    fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);
    if (fd < 0)
        return -1;
    if(ioctl(fd, UI_SET_EVBIT, EV_ABS)<0) return -4;


    for(i=0;analog_axis_list[i]>=0;i++){
        if(ioctl(fd,UI_SET_ABSBIT,analog_axis_list[i])<0) return -5;
        dev.absmax[analog_axis_list[i]]=32767;
        dev.absmin[analog_axis_list[i]]=-32768;
    }

    const char *cparam = (*env)->GetStringUTFChars(env, param, 0);
    snprintf(dev.name, UINPUT_MAX_NAME_SIZE, cparam);
    (*env)->ReleaseStringUTFChars(env, param, cparam);
    dev.id.bustype = BUS_VIRTUAL;
    dev.id.vendor = param2;
    dev.id.product = param3;
    dev.id.version = 1;

    if (write(fd, &dev, sizeof(dev)) < 0)
        return -7;

    if (ioctl(fd, UI_DEV_CREATE) < 0)
        return -8;
    return 0;

}

The device is successfully created, and the return value is 0. Inside input.h the ABS values are so defined:

#define ABS_X  0x00
#define ABS_Y  0x01
#define ABS_RX 0x03
#define ABS_RY 0x04

But when checking the axis on android, I get proper values for AXIS_X and AXIS_Y, but ABS_RX and ABS_RY have wrong values. I used this code to check the axis values:

InputDevice device = InputDevice.getDevice(ids[position]);
List<InputDevice.MotionRange> ranges = device.getMotionRanges();
StringBuilder sb = new StringBuilder("");
if(ranges.size()==0){
    sb.append("NO_MOTION_RANGES");
}
else{
    int i = 0;
    for(InputDevice.MotionRange range:ranges) {
        if(i>0) {
            sb.append(",");
        }
        sb.append(MotionEvent.axisToString(range.getAxis()));
        sb.append("(").append(range.getAxis()).append(")");
        i++;
    }
}
return sb.toString();

And the result is:

AXIS_X(0),AXIS_Y(1),AXIS_Z(11),AXIS_RZ(14)

I am using the latest NDK release (r10d) without any particular settings enabled. What can cause these errors?

I want to point out that it's my code to have something wrong, because with an actual controller the axis numbers are correct.

Edit 1: I tried to return analog_axis_list[2], which is ABS_RX, at the end of my function instead of 0 and it returns 3, so I think I'm passing a wrong type to the ioctl call. Which type should I choose?

Answer 1

Android uses AXIS_Z and AXIS_RZ for the right stick; this is consistent with USB HID.