Function hid_read_timeout

lib/hidapi/linux/hid.c:1043–1093

int HID_API_EXPORT hid_read_timeout(hid_device *dev, unsigned char *data, size_t length, int milliseconds)
{
	/* Set device error to none */
	register_device_error(dev, NULL);

	int bytes_read;

	if (milliseconds >= 0) {
		/* Milliseconds is either 0 (non-blocking) or > 0 (contains
		   a valid timeout). In both cases we want to call poll()
		   and wait for data to arrive.  Don't rely on non-blocking
		   operation (O_NONBLOCK) since some kernels don't seem to
		   properly report device disconnection through read() when
		   in non-blocking mode.  */
		int ret;
		struct pollfd fds;

		fds.fd = dev->device_handle;
		fds.events = POLLIN;
		fds.revents = 0;
		ret = poll(&fds, 1, milliseconds);
		if (ret == 0) {
			/* Timeout */
			return ret;
		}
		if (ret == -1) {
			/* Error */
			register_device_error(dev, strerror(errno));
			return ret;
		}
		else {
			/* Check for errors on the file descriptor. This will
			   indicate a device disconnection. */
			if (fds.revents & (POLLERR | POLLHUP | POLLNVAL)) {
				// We cannot use strerror() here as no -1 was returned from poll().
				register_device_error(dev, "hid_read_timeout: unexpected poll error (device disconnected)");
				return -1;
			}
		}
	}

	bytes_read = read(dev->device_handle, data, length);
	if (bytes_read < 0) {
		if (errno == EAGAIN || errno == EINPROGRESS)
			bytes_read = 0;
		else
			register_device_error(dev, strerror(errno));
	}

	return bytes_read;
}

int HID_API_EXPORT hid_read(hid_device *dev, unsigned char *data, size_t length)
{