Login Logout Codeigniter

controller

public function login(){
	if ($_POST) {
		$result = $this->Mahasiswa->login();
		if (!empty($result)) {
			$data = array(
				'username'=>$result->username,
				'fullname'=>$result->fullname
			);
			$this->session->set_userdata($data);
			redirect('pendaftaran/data');
		}else{
			$this->session->set_flashdata('message','Username atau password salah!');
			redirect('pendaftaran/login');
		}
	}
	$this->load->view('pendaftaran/header');	
	$this->load->view('pendaftaran/login');
	$this->load->view('pendaftaran/footer');
}

public function logout(){
	$data = array('username','fullname');
	$this->session->unset_userdata($data);

	redirect('pendaftaran/login');
}
public function data(){
	if (empty($this->session->userdata('username'))) {
		$this->session->set_flashdata('message','Anda harus login dulu');
		redirect('pendaftaran/login');
	}
	$data['results'] = $this->Mahasiswa->getData();
	$this->load->view('pendaftaran/header');	
	$this->load->view('pendaftaran/data',$data);
	$this->load->view('pendaftaran/footer');	

}

model

public function login(){
	$username = $this->input->post('username');
	$password = sha1($this->input->post('password'));
	$this->db->where('username',$username);
	$this->db->where('password',$password);
	return $this->db->get('users')->row();
}

view login

<div class="container center-block">
<div class="panel panel-default center-block" style="max-width:600px;margin-top:70px">
  <div class="panel-heading">
    <h3 class="panel-title">Login Form</h3>
  </div>
  <div class="panel-body">
  	<?php if (($this->session->flashdata('message'))): ?>
  		<div class="alert alert-danger">
  			<?php echo $this->session->flashdata('message') ?>
  		</div>
  	<?php endif ?>
    <form action="<?php echo site_url() ?>/pendaftaran/login" method="POST" class="form-horizontal">
		<div class="form-group">
			<label for="username" class="col-sm-4 control-label">Username</label>
			<div class="col-sm-8">
				<input type="text" name="username" id="username" class="form-control">
			</div>
		</div>
		<div class="form-group">
			<label for="password" class="col-sm-4 control-label">Password</label>
			<div class="col-sm-8">
				<input type="password" name="password" id="password" class="form-control">
			</div>
		</div>
		<div class="form-group">
			<div class="col-sm-offset-2 col-sm-10">
				<input type="submit" class="btn btn-primary" value="Login">
			</div>
		</div>
	</form>

  </div>
</div>
</div>