Android N libusb_init returns -1 failed to initialize libusb

Question

I am using libusb library in my android application. I build this library and added *.so files for all architecture.

I am calling libusb_init to initialize it but it returns -1 always. I am not sure if this permission issue or what.

failed to initialize libusb

I see libusb_init method code inside library:

/** \ingroup lib
 * Initialize libusb. This function must be called before calling any other
 * libusb function.
 *
 * If you do not provide an output location for a context pointer, a default
 * context will be created. If there was already a default context, it will
 * be reused (and nothing will be initialized/reinitialized).
 *
 * \param context Optional output location for context pointer.
 * Only valid on return code 0.
 * \returns 0 on success, or a LIBUSB_ERROR code on failure
 * \see contexts
 */
int API_EXPORTED libusb_init(libusb_context **context)
{
    char *dbg = getenv("LIBUSB_DEBUG");
    struct libusb_context *ctx;
    int r = 0;

    usbi_mutex_static_lock(&default_context_lock);
    if (!context && usbi_default_context) {
        usbi_dbg("reusing default context");
        default_context_refcnt++;
        usbi_mutex_static_unlock(&default_context_lock);
        return 0;
    }

    ctx = malloc(sizeof(*ctx));
    if (!ctx) {
        r = LIBUSB_ERROR_NO_MEM;
        goto err_unlock;
    }
    memset(ctx, 0, sizeof(*ctx));

    if (dbg) {
        ctx->debug = atoi(dbg);
        if (ctx->debug)
            ctx->debug_fixed = 1;
    }

    usbi_dbg("libusb-%d.%d.%d%s%s%s",
             libusb_version_internal.major,
             libusb_version_internal.minor,
             libusb_version_internal.micro,
             libusb_version_internal.rc,
             libusb_version_internal.describe[0] ? " git:" : "",
             libusb_version_internal.describe);

    if (usbi_backend->init) {
        r = usbi_backend->init(ctx);
        if (r)
            goto err_free_ctx;
    }

    usbi_mutex_init(&ctx->usb_devs_lock, NULL);
    usbi_mutex_init(&ctx->open_devs_lock, NULL);
    list_init(&ctx->usb_devs);
    list_init(&ctx->open_devs);

    r = usbi_io_init(ctx);
    if (r < 0) {
        if (usbi_backend->exit)
            usbi_backend->exit();
        goto err_destroy_mutex;
    }

    if (context) {
        *context = ctx;
    } else if (!usbi_default_context) {
        usbi_dbg("created default context");
        usbi_default_context = ctx;
        default_context_refcnt++;
    }
    usbi_mutex_static_unlock(&default_context_lock);

    return 0;

err_destroy_mutex:
    usbi_mutex_destroy(&ctx->open_devs_lock);
    usbi_mutex_destroy(&ctx->usb_devs_lock);
err_free_ctx:
    free(ctx);
err_unlock:
    usbi_mutex_static_unlock(&default_context_lock);
    return r;
}

I debugged it and found flow returns from this line of above method with -1 code.

if (usbi_backend->init) {
    r = usbi_backend->init(ctx);
    if (r)
        goto err_free_ctx;
}

I am calling this from java code with JNI wrapper

class MainActivity : AppCompatActivity(), AnkoLogger {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        button.setOnClickListener {
            val ret = initUSB()
            toast(ret)
        }
    }

    init {
        System.loadLibrary("usbnok");
    }

    /*
     * native function prototypes
     */
    external fun initUSB(): String
}

JNI Wrapper

jstring Java_com_williams_poc_MainActivity_initUSB( JNIEnv* env, jobject thiz )
{
  int r;
  __android_log_print(ANDROID_LOG_INFO, LOG_TAG, "entering iniUSB");
  r = libusb_init(NULL);
    if(r < 0) {
    __android_log_print(ANDROID_LOG_INFO, LOG_TAG, "failed to initialize libusb");
    return  (*env)->NewStringUTF(env, "Failed to initialize libusb");
  } else {
    __android_log_print(ANDROID_LOG_INFO, LOG_TAG, "successfully initialized libusb");
    return (*env)->NewStringUTF(env, "libusb successfully enabled");
  }
}

Does anyone know when it returns -1? What could be the issue ? Thanks in advance.

Answer 1

You Must Use LibUsb Version v1.0.23 +

Then libusb_init to initialize success.

Answer 2

Compatibility with Android 7+ is a known issue for libusb.

Kuldeep Singh Dhaka and Martin Marinov have modified versions that work a treat for Androids 4-6, but you need to open the device a special way. Instructions are in Kuldeep's GitHub repo.

As far as I'm aware, no-one as of yet has got a modified version of libusb running on Android N.

If you can get it working, please post on the mailing list. Everyone would love to hear how you did it.

~Chris