<form method="post" enctype="multipart/form-data">
  <input type="file" name="file_upload">
  <input type="submit" name="save" value='upload'>
</form>

public function formupload()
	{
		if($this->input->post('save'))
		{
		$config['upload_path'] = './uploads/products/';
        $config['allowed_types'] = 'gif|jpg|png|jpeg';
        $config['max_size'] = 2000;
        $config['max_width'] = 1500;
        $config['max_height'] = 1500;
        $this->load->library('upload', $config);
		if (!$this->upload->do_upload('file_upload')) 
		{
            $error = array('error' => $this->upload->display_errors());
			print_r($error);
			exit;
        } 
		else 
		{
			$data = $this->upload->data();
			$fileData[] = $data;
                foreach ($fileData as $file) {
                    $file_data = $file;
                }
                var_dump($file_data);
				$this->db->insert('tbl_name', array(
                    'file_upload' => $file_data['file_name'],
                ));
				redirect('your_url');
        	}
		}  
	}