/*
   * llc_station.c - station component of LLC
   *
   * Copyright (c) 1997 by Procom Technology, Inc.
   * 		 2001-2003 by Arnaldo Carvalho de Melo <acme@conectiva.com.br>
   *
   * This program can be redistributed or modified under the terms of the
   * GNU General Public License as published by the Free Software Foundation.
   * This program is distributed without any warranty or implied warranty
   * of merchantability or fitness for a particular purpose.
   *
   * See the GNU General Public License for more details.
   */

  #include <linux/init.h>
  #include <linux/module.h>

  #include <linux/slab.h>

  #include <net/llc.h>
  #include <net/llc_sap.h>
  #include <net/llc_conn.h>
  #include <net/llc_c_ac.h>
  #include <net/llc_s_ac.h>
  #include <net/llc_c_ev.h>
  #include <net/llc_c_st.h>
  #include <net/llc_s_ev.h>
  #include <net/llc_s_st.h>
  #include <net/llc_pdu.h>
  
  /**
   * struct llc_station - LLC station component
   *
   * SAP and connection resource manager, one per adapter.
   *
   * @state - state of station
   * @xid_r_count - XID response PDU counter
   * @mac_sa - MAC source address
   * @sap_list - list of related SAPs
   * @ev_q - events entering state mach.
   * @mac_pdu_q - PDUs ready to send to MAC
   */
  struct llc_station {
  	u8			    state;
  	u8			    xid_r_count;
  	struct timer_list	    ack_timer;
  	u8			    retry_count;
  	u8			    maximum_retry;
  	struct {
  		struct sk_buff_head list;
  		spinlock_t	    lock;
  	} ev_q;
  	struct sk_buff_head	    mac_pdu_q;
  };

  #define LLC_STATION_ACK_TIME (3 * HZ)
  
  int sysctl_llc_station_ack_timeout = LLC_STATION_ACK_TIME;

  /* Types of events (possible values in 'ev->type') */
  #define LLC_STATION_EV_TYPE_SIMPLE	1
  #define LLC_STATION_EV_TYPE_CONDITION	2
  #define LLC_STATION_EV_TYPE_PRIM	3
  #define LLC_STATION_EV_TYPE_PDU		4       /* command/response PDU */
  #define LLC_STATION_EV_TYPE_ACK_TMR	5
  #define LLC_STATION_EV_TYPE_RPT_STATUS	6
  
  /* Events */
  #define LLC_STATION_EV_ENABLE_WITH_DUP_ADDR_CHECK		1
  #define LLC_STATION_EV_ENABLE_WITHOUT_DUP_ADDR_CHECK		2
  #define LLC_STATION_EV_ACK_TMR_EXP_LT_RETRY_CNT_MAX_RETRY	3
  #define LLC_STATION_EV_ACK_TMR_EXP_EQ_RETRY_CNT_MAX_RETRY	4
  #define LLC_STATION_EV_RX_NULL_DSAP_XID_C			5
  #define LLC_STATION_EV_RX_NULL_DSAP_0_XID_R_XID_R_CNT_EQ	6
  #define LLC_STATION_EV_RX_NULL_DSAP_1_XID_R_XID_R_CNT_EQ	7
  #define LLC_STATION_EV_RX_NULL_DSAP_TEST_C			8
  #define LLC_STATION_EV_DISABLE_REQ				9
  
  struct llc_station_state_ev {
  	u8		 type;
  	u8		 prim;
  	u8		 prim_type;
  	u8		 reason;
  	struct list_head node; /* node in station->ev_q.list */
  };
  
  static __inline__ struct llc_station_state_ev *
  					llc_station_ev(struct sk_buff *skb)
  {
  	return (struct llc_station_state_ev *)skb->cb;
  }
  
  typedef int (*llc_station_ev_t)(struct sk_buff *skb);
  
  #define LLC_STATION_STATE_DOWN		1	/* initial state */
  #define LLC_STATION_STATE_DUP_ADDR_CHK	2
  #define LLC_STATION_STATE_UP		3
  
  #define LLC_NBR_STATION_STATES		3	/* size of state table */
  
  typedef int (*llc_station_action_t)(struct sk_buff *skb);
  
  /* Station component state table structure */
  struct llc_station_state_trans {
  	llc_station_ev_t ev;
  	u8 next_state;
  	llc_station_action_t *ev_actions;
  };
  
  struct llc_station_state {
  	u8 curr_state;
  	struct llc_station_state_trans **transitions;
  };
  
  static struct llc_station llc_main_station;
  
  static int llc_stat_ev_enable_with_dup_addr_check(struct sk_buff *skb)
  {

  	struct llc_station_state_ev *ev = llc_station_ev(skb);

  	return ev->type == LLC_STATION_EV_TYPE_SIMPLE &&
  	       ev->prim_type ==

  			      LLC_STATION_EV_ENABLE_WITH_DUP_ADDR_CHECK ? 0 : 1;

  }
  
  static int llc_stat_ev_enable_without_dup_addr_check(struct sk_buff *skb)
  {

  	struct llc_station_state_ev *ev = llc_station_ev(skb);

  	return ev->type == LLC_STATION_EV_TYPE_SIMPLE &&
  	       ev->prim_type ==
  			LLC_STATION_EV_ENABLE_WITHOUT_DUP_ADDR_CHECK ? 0 : 1;
  }
  
  static int llc_stat_ev_ack_tmr_exp_lt_retry_cnt_max_retry(struct sk_buff *skb)
  {

  	struct llc_station_state_ev *ev = llc_station_ev(skb);

  	return ev->type == LLC_STATION_EV_TYPE_ACK_TMR &&
  		llc_main_station.retry_count <
  		llc_main_station.maximum_retry ? 0 : 1;
  }
  
  static int llc_stat_ev_ack_tmr_exp_eq_retry_cnt_max_retry(struct sk_buff *skb)
  {

  	struct llc_station_state_ev *ev = llc_station_ev(skb);

  	return ev->type == LLC_STATION_EV_TYPE_ACK_TMR &&
  		llc_main_station.retry_count ==
  		llc_main_station.maximum_retry ? 0 : 1;
  }
  
  static int llc_stat_ev_rx_null_dsap_xid_c(struct sk_buff *skb)
  {

  	struct llc_station_state_ev *ev = llc_station_ev(skb);

  	struct llc_pdu_un *pdu = llc_pdu_un_hdr(skb);
  
  	return ev->type == LLC_STATION_EV_TYPE_PDU &&
  	       LLC_PDU_IS_CMD(pdu) &&			/* command PDU */
  	       LLC_PDU_TYPE_IS_U(pdu) &&		/* U type PDU */
  	       LLC_U_PDU_CMD(pdu) == LLC_1_PDU_CMD_XID &&
  	       !pdu->dsap ? 0 : 1;			/* NULL DSAP value */
  }
  
  static int llc_stat_ev_rx_null_dsap_0_xid_r_xid_r_cnt_eq(struct sk_buff *skb)
  {
  	struct llc_station_state_ev *ev = llc_station_ev(skb);
  	struct llc_pdu_un *pdu = llc_pdu_un_hdr(skb);
  
  	return ev->type == LLC_STATION_EV_TYPE_PDU &&
  	       LLC_PDU_IS_RSP(pdu) &&			/* response PDU */
  	       LLC_PDU_TYPE_IS_U(pdu) &&		/* U type PDU */
  	       LLC_U_PDU_RSP(pdu) == LLC_1_PDU_CMD_XID &&
  	       !pdu->dsap &&				/* NULL DSAP value */
  	       !llc_main_station.xid_r_count ? 0 : 1;
  }
  
  static int llc_stat_ev_rx_null_dsap_1_xid_r_xid_r_cnt_eq(struct sk_buff *skb)
  {
  	struct llc_station_state_ev *ev = llc_station_ev(skb);
  	struct llc_pdu_un *pdu = llc_pdu_un_hdr(skb);
  
  	return ev->type == LLC_STATION_EV_TYPE_PDU &&
  	       LLC_PDU_IS_RSP(pdu) &&			/* response PDU */
  	       LLC_PDU_TYPE_IS_U(pdu) &&		/* U type PDU */
  	       LLC_U_PDU_RSP(pdu) == LLC_1_PDU_CMD_XID &&
  	       !pdu->dsap &&				/* NULL DSAP value */
  	       llc_main_station.xid_r_count == 1 ? 0 : 1;
  }
  
  static int llc_stat_ev_rx_null_dsap_test_c(struct sk_buff *skb)
  {
  	struct llc_station_state_ev *ev = llc_station_ev(skb);
  	struct llc_pdu_un *pdu = llc_pdu_un_hdr(skb);
  
  	return ev->type == LLC_STATION_EV_TYPE_PDU &&
  	       LLC_PDU_IS_CMD(pdu) &&			/* command PDU */
  	       LLC_PDU_TYPE_IS_U(pdu) &&		/* U type PDU */
  	       LLC_U_PDU_CMD(pdu) == LLC_1_PDU_CMD_TEST &&
  	       !pdu->dsap ? 0 : 1;			/* NULL DSAP */
  }
  
  static int llc_stat_ev_disable_req(struct sk_buff *skb)
  {
  	struct llc_station_state_ev *ev = llc_station_ev(skb);
  
  	return ev->type == LLC_STATION_EV_TYPE_PRIM &&
  	       ev->prim == LLC_DISABLE_PRIM &&
  	       ev->prim_type == LLC_PRIM_TYPE_REQ ? 0 : 1;
  }
  
  /**
   *	llc_station_send_pdu - queues PDU to send
   *	@skb: Address of the PDU
   *
   *	Queues a PDU to send to the MAC layer.
   */
  static void llc_station_send_pdu(struct sk_buff *skb)
  {
  	skb_queue_tail(&llc_main_station.mac_pdu_q, skb);
  	while ((skb = skb_dequeue(&llc_main_station.mac_pdu_q)) != NULL)
  		if (dev_queue_xmit(skb))
  			break;
  }
  
  static int llc_station_ac_start_ack_timer(struct sk_buff *skb)
  {

  	mod_timer(&llc_main_station.ack_timer,
  		  jiffies + sysctl_llc_station_ack_timeout);

  	return 0;
  }
  
  static int llc_station_ac_set_retry_cnt_0(struct sk_buff *skb)
  {
  	llc_main_station.retry_count = 0;
  	return 0;
  }
  
  static int llc_station_ac_inc_retry_cnt_by_1(struct sk_buff *skb)
  {
  	llc_main_station.retry_count++;
  	return 0;
  }
  
  static int llc_station_ac_set_xid_r_cnt_0(struct sk_buff *skb)
  {
  	llc_main_station.xid_r_count = 0;
  	return 0;
  }
  
  static int llc_station_ac_inc_xid_r_cnt_by_1(struct sk_buff *skb)
  {
  	llc_main_station.xid_r_count++;
  	return 0;
  }
  
  static int llc_station_ac_send_null_dsap_xid_c(struct sk_buff *skb)
  {
  	int rc = 1;

  	struct sk_buff *nskb = llc_alloc_frame(NULL, skb->dev, LLC_PDU_TYPE_U,
  					       sizeof(struct llc_xid_info));

  
  	if (!nskb)
  		goto out;
  	llc_pdu_header_init(nskb, LLC_PDU_TYPE_U, 0, 0, LLC_PDU_CMD);
  	llc_pdu_init_as_xid_cmd(nskb, LLC_XID_NULL_CLASS_2, 127);

  	rc = llc_mac_hdr_init(nskb, skb->dev->dev_addr, skb->dev->dev_addr);

  	if (unlikely(rc))

  		goto free;
  	llc_station_send_pdu(nskb);
  out:
  	return rc;
  free:
  	kfree_skb(skb);
  	goto out;
  }
  
  static int llc_station_ac_send_xid_r(struct sk_buff *skb)
  {
  	u8 mac_da[ETH_ALEN], dsap;
  	int rc = 1;

  	struct sk_buff *nskb = llc_alloc_frame(NULL, skb->dev, LLC_PDU_TYPE_U,
  					       sizeof(struct llc_xid_info));

  
  	if (!nskb)
  		goto out;
  	rc = 0;

  	llc_pdu_decode_sa(skb, mac_da);
  	llc_pdu_decode_ssap(skb, &dsap);
  	llc_pdu_header_init(nskb, LLC_PDU_TYPE_U, 0, dsap, LLC_PDU_RSP);
  	llc_pdu_init_as_xid_rsp(nskb, LLC_XID_NULL_CLASS_2, 127);

  	rc = llc_mac_hdr_init(nskb, skb->dev->dev_addr, mac_da);

  	if (unlikely(rc))

  		goto free;
  	llc_station_send_pdu(nskb);
  out:
  	return rc;
  free:
  	kfree_skb(skb);
  	goto out;
  }
  
  static int llc_station_ac_send_test_r(struct sk_buff *skb)
  {
  	u8 mac_da[ETH_ALEN], dsap;
  	int rc = 1;

  	u32 data_size;
  	struct sk_buff *nskb;
  
  	/* The test request command is type U (llc_len = 3) */
  	data_size = ntohs(eth_hdr(skb)->h_proto) - 3;
  	nskb = llc_alloc_frame(NULL, skb->dev, LLC_PDU_TYPE_U, data_size);

  
  	if (!nskb)
  		goto out;
  	rc = 0;

  	llc_pdu_decode_sa(skb, mac_da);
  	llc_pdu_decode_ssap(skb, &dsap);
  	llc_pdu_header_init(nskb, LLC_PDU_TYPE_U, 0, dsap, LLC_PDU_RSP);

  	llc_pdu_init_as_test_rsp(nskb, skb);

  	rc = llc_mac_hdr_init(nskb, skb->dev->dev_addr, mac_da);

  	if (unlikely(rc))

  		goto free;
  	llc_station_send_pdu(nskb);
  out:
  	return rc;
  free:
  	kfree_skb(skb);
  	goto out;
  }
  
  static int llc_station_ac_report_status(struct sk_buff *skb)
  {
  	return 0;
  }
  
  /* COMMON STATION STATE transitions */
  
  /* dummy last-transition indicator; common to all state transition groups
   * last entry for this state
   * all members are zeros, .bss zeroes it
   */
  static struct llc_station_state_trans llc_stat_state_trans_end;
  
  /* DOWN STATE transitions */
  
  /* state transition for LLC_STATION_EV_ENABLE_WITH_DUP_ADDR_CHECK event */
  static llc_station_action_t llc_stat_down_state_actions_1[] = {
  	[0] = llc_station_ac_start_ack_timer,
  	[1] = llc_station_ac_set_retry_cnt_0,
  	[2] = llc_station_ac_set_xid_r_cnt_0,
  	[3] = llc_station_ac_send_null_dsap_xid_c,
  	[4] = NULL,
  };
  
  static struct llc_station_state_trans llc_stat_down_state_trans_1 = {
  	.ev	    = llc_stat_ev_enable_with_dup_addr_check,
  	.next_state = LLC_STATION_STATE_DUP_ADDR_CHK,
  	.ev_actions = llc_stat_down_state_actions_1,
  };
  
  /* state transition for LLC_STATION_EV_ENABLE_WITHOUT_DUP_ADDR_CHECK event */
  static llc_station_action_t llc_stat_down_state_actions_2[] = {
  	[0] = llc_station_ac_report_status,	/* STATION UP */
  	[1] = NULL,
  };
  
  static struct llc_station_state_trans llc_stat_down_state_trans_2 = {
  	.ev	    = llc_stat_ev_enable_without_dup_addr_check,
  	.next_state = LLC_STATION_STATE_UP,
  	.ev_actions = llc_stat_down_state_actions_2,
  };
  
  /* array of pointers; one to each transition */
  static struct llc_station_state_trans *llc_stat_dwn_state_trans[] = {
  	[0] = &llc_stat_down_state_trans_1,
  	[1] = &llc_stat_down_state_trans_2,
  	[2] = &llc_stat_state_trans_end,
  };
  
  /* UP STATE transitions */
  /* state transition for LLC_STATION_EV_DISABLE_REQ event */
  static llc_station_action_t llc_stat_up_state_actions_1[] = {
  	[0] = llc_station_ac_report_status,	/* STATION DOWN */
  	[1] = NULL,
  };
  
  static struct llc_station_state_trans llc_stat_up_state_trans_1 = {
  	.ev	    = llc_stat_ev_disable_req,
  	.next_state = LLC_STATION_STATE_DOWN,
  	.ev_actions = llc_stat_up_state_actions_1,
  };
  
  /* state transition for LLC_STATION_EV_RX_NULL_DSAP_XID_C event */
  static llc_station_action_t llc_stat_up_state_actions_2[] = {
  	[0] = llc_station_ac_send_xid_r,
  	[1] = NULL,
  };
  
  static struct llc_station_state_trans llc_stat_up_state_trans_2 = {
  	.ev	    = llc_stat_ev_rx_null_dsap_xid_c,
  	.next_state = LLC_STATION_STATE_UP,
  	.ev_actions = llc_stat_up_state_actions_2,
  };
  
  /* state transition for LLC_STATION_EV_RX_NULL_DSAP_TEST_C event */
  static llc_station_action_t llc_stat_up_state_actions_3[] = {
  	[0] = llc_station_ac_send_test_r,
  	[1] = NULL,
  };
  
  static struct llc_station_state_trans llc_stat_up_state_trans_3 = {
  	.ev	    = llc_stat_ev_rx_null_dsap_test_c,
  	.next_state = LLC_STATION_STATE_UP,
  	.ev_actions = llc_stat_up_state_actions_3,
  };
  
  /* array of pointers; one to each transition */
  static struct llc_station_state_trans *llc_stat_up_state_trans [] = {
  	[0] = &llc_stat_up_state_trans_1,
  	[1] = &llc_stat_up_state_trans_2,
  	[2] = &llc_stat_up_state_trans_3,
  	[3] = &llc_stat_state_trans_end,
  };
  
  /* DUP ADDR CHK STATE transitions */
  /* state transition for LLC_STATION_EV_RX_NULL_DSAP_0_XID_R_XID_R_CNT_EQ
   * event
   */
  static llc_station_action_t llc_stat_dupaddr_state_actions_1[] = {
  	[0] = llc_station_ac_inc_xid_r_cnt_by_1,
  	[1] = NULL,
  };
  
  static struct llc_station_state_trans llc_stat_dupaddr_state_trans_1 = {
  	.ev	    = llc_stat_ev_rx_null_dsap_0_xid_r_xid_r_cnt_eq,
  	.next_state = LLC_STATION_STATE_DUP_ADDR_CHK,
  	.ev_actions = llc_stat_dupaddr_state_actions_1,
  };
  
  /* state transition for LLC_STATION_EV_RX_NULL_DSAP_1_XID_R_XID_R_CNT_EQ
   * event
   */
  static llc_station_action_t llc_stat_dupaddr_state_actions_2[] = {
  	[0] = llc_station_ac_report_status,	/* DUPLICATE ADDRESS FOUND */
  	[1] = NULL,
  };
  
  static struct llc_station_state_trans llc_stat_dupaddr_state_trans_2 = {
  	.ev	    = llc_stat_ev_rx_null_dsap_1_xid_r_xid_r_cnt_eq,
  	.next_state = LLC_STATION_STATE_DOWN,
  	.ev_actions = llc_stat_dupaddr_state_actions_2,
  };
  
  /* state transition for LLC_STATION_EV_RX_NULL_DSAP_XID_C event */
  static llc_station_action_t llc_stat_dupaddr_state_actions_3[] = {
  	[0] = llc_station_ac_send_xid_r,
  	[1] = NULL,
  };
  
  static struct llc_station_state_trans llc_stat_dupaddr_state_trans_3 = {
  	.ev	    = llc_stat_ev_rx_null_dsap_xid_c,
  	.next_state = LLC_STATION_STATE_DUP_ADDR_CHK,
  	.ev_actions = llc_stat_dupaddr_state_actions_3,
  };
  
  /* state transition for LLC_STATION_EV_ACK_TMR_EXP_LT_RETRY_CNT_MAX_RETRY
   * event
   */
  static llc_station_action_t llc_stat_dupaddr_state_actions_4[] = {
  	[0] = llc_station_ac_start_ack_timer,
  	[1] = llc_station_ac_inc_retry_cnt_by_1,
  	[2] = llc_station_ac_set_xid_r_cnt_0,
  	[3] = llc_station_ac_send_null_dsap_xid_c,
  	[4] = NULL,
  };
  
  static struct llc_station_state_trans llc_stat_dupaddr_state_trans_4 = {
  	.ev	    = llc_stat_ev_ack_tmr_exp_lt_retry_cnt_max_retry,
  	.next_state = LLC_STATION_STATE_DUP_ADDR_CHK,
  	.ev_actions = llc_stat_dupaddr_state_actions_4,
  };
  
  /* state transition for LLC_STATION_EV_ACK_TMR_EXP_EQ_RETRY_CNT_MAX_RETRY
   * event
   */
  static llc_station_action_t llc_stat_dupaddr_state_actions_5[] = {
  	[0] = llc_station_ac_report_status,	/* STATION UP */
  	[1] = NULL,
  };
  
  static struct llc_station_state_trans llc_stat_dupaddr_state_trans_5 = {
  	.ev	    = llc_stat_ev_ack_tmr_exp_eq_retry_cnt_max_retry,
  	.next_state = LLC_STATION_STATE_UP,
  	.ev_actions = llc_stat_dupaddr_state_actions_5,
  };
  
  /* state transition for LLC_STATION_EV_DISABLE_REQ event */
  static llc_station_action_t llc_stat_dupaddr_state_actions_6[] = {
  	[0] = llc_station_ac_report_status,	/* STATION DOWN */
  	[1] = NULL,
  };
  
  static struct llc_station_state_trans llc_stat_dupaddr_state_trans_6 = {
  	.ev	    = llc_stat_ev_disable_req,
  	.next_state = LLC_STATION_STATE_DOWN,
  	.ev_actions = llc_stat_dupaddr_state_actions_6,
  };
  
  /* array of pointers; one to each transition */
  static struct llc_station_state_trans *llc_stat_dupaddr_state_trans[] = {
  	[0] = &llc_stat_dupaddr_state_trans_6,	/* Request */
  	[1] = &llc_stat_dupaddr_state_trans_4,	/* Timer */
  	[2] = &llc_stat_dupaddr_state_trans_5,
  	[3] = &llc_stat_dupaddr_state_trans_1,	/* Receive frame */
  	[4] = &llc_stat_dupaddr_state_trans_2,
  	[5] = &llc_stat_dupaddr_state_trans_3,
  	[6] = &llc_stat_state_trans_end,
  };
  
  static struct llc_station_state
  			llc_station_state_table[LLC_NBR_STATION_STATES] = {
  	[LLC_STATION_STATE_DOWN - 1] = {
  		.curr_state  = LLC_STATION_STATE_DOWN,
  		.transitions = llc_stat_dwn_state_trans,
  	},
  	[LLC_STATION_STATE_DUP_ADDR_CHK - 1] = {
  		.curr_state  = LLC_STATION_STATE_DUP_ADDR_CHK,
  		.transitions = llc_stat_dupaddr_state_trans,
  	},
  	[LLC_STATION_STATE_UP - 1] = {
  		.curr_state  = LLC_STATION_STATE_UP,
  		.transitions = llc_stat_up_state_trans,
  	},
  };
  
  /**
   *	llc_exec_station_trans_actions - executes actions for transition
   *	@trans: Address of the transition
   *	@skb: Address of the event that caused the transition
   *
   *	Executes actions of a transition of the station state machine. Returns
   *	0 if all actions complete successfully, nonzero otherwise.
   */
  static u16 llc_exec_station_trans_actions(struct llc_station_state_trans *trans,
  					  struct sk_buff *skb)
  {
  	u16 rc = 0;
  	llc_station_action_t *next_action = trans->ev_actions;
  
  	for (; next_action && *next_action; next_action++)
  		if ((*next_action)(skb))
  			rc = 1;
  	return rc;
  }
  
  /**
   *	llc_find_station_trans - finds transition for this event
   *	@skb: Address of the event
   *
   *	Search thru events of the current state of the station until list
   *	exhausted or it's obvious that the event is not valid for the current
   *	state. Returns the address of the transition if cound, %NULL otherwise.
   */
  static struct llc_station_state_trans *
  				llc_find_station_trans(struct sk_buff *skb)
  {
  	int i = 0;
  	struct llc_station_state_trans *rc = NULL;
  	struct llc_station_state_trans **next_trans;
  	struct llc_station_state *curr_state =
  				&llc_station_state_table[llc_main_station.state - 1];
  
  	for (next_trans = curr_state->transitions; next_trans[i]->ev; i++)
  		if (!next_trans[i]->ev(skb)) {
  			rc = next_trans[i];
  			break;
  		}
  	return rc;
  }
  
  /**
   *	llc_station_free_ev - frees an event
   *	@skb: Address of the event
   *
   *	Frees an event.
   */
  static void llc_station_free_ev(struct sk_buff *skb)
  {
  	struct llc_station_state_ev *ev = llc_station_ev(skb);
  
  	if (ev->type == LLC_STATION_EV_TYPE_PDU)
  		kfree_skb(skb);
  }
  
  /**
   *	llc_station_next_state - processes event and goes to the next state
   *	@skb: Address of the event
   *
   *	Processes an event, executes any transitions related to that event and
   *	updates the state of the station.
   */
  static u16 llc_station_next_state(struct sk_buff *skb)
  {
  	u16 rc = 1;
  	struct llc_station_state_trans *trans;
  
  	if (llc_main_station.state > LLC_NBR_STATION_STATES)
  		goto out;
  	trans = llc_find_station_trans(skb);
  	if (trans) {
  		/* got the state to which we next transition; perform the
  		 * actions associated with this transition before actually
  		 * transitioning to the next state
  		 */
  		rc = llc_exec_station_trans_actions(trans, skb);
  		if (!rc)
  			/* transition station to next state if all actions
  			 * execute successfully; done; wait for next event
  			 */
  			llc_main_station.state = trans->next_state;
  	} else
  		/* event not recognized in current state; re-queue it for
  		 * processing again at a later time; return failure
  		 */
  		rc = 0;
  out:
  	llc_station_free_ev(skb);
  	return rc;
  }
  
  /**
   *	llc_station_service_events - service events in the queue
   *
   *	Get an event from the station event queue (if any); attempt to service
   *	the event; if event serviced, get the next event (if any) on the event
   *	queue; if event not service, re-queue the event on the event queue and
   *	attempt to service the next event; when serviced all events in queue,
   *	finished; if don't transition to different state, just service all
   *	events once; if transition to new state, service all events again.
   *	Caller must hold llc_main_station.ev_q.lock.
   */
  static void llc_station_service_events(void)
  {
  	struct sk_buff *skb;
  
  	while ((skb = skb_dequeue(&llc_main_station.ev_q.list)) != NULL)
  		llc_station_next_state(skb);
  }
  
  /**
   *	llc_station_state_process: queue event and try to process queue.
   *	@skb: Address of the event
   *
   *	Queues an event (on the station event queue) for handling by the
   *	station state machine and attempts to process any queued-up events.
   */
  static void llc_station_state_process(struct sk_buff *skb)
  {
  	spin_lock_bh(&llc_main_station.ev_q.lock);
  	skb_queue_tail(&llc_main_station.ev_q.list, skb);
  	llc_station_service_events();
  	spin_unlock_bh(&llc_main_station.ev_q.lock);
  }
  
  static void llc_station_ack_tmr_cb(unsigned long timeout_data)
  {
  	struct sk_buff *skb = alloc_skb(0, GFP_ATOMIC);
  
  	if (skb) {
  		struct llc_station_state_ev *ev = llc_station_ev(skb);
  
  		ev->type = LLC_STATION_EV_TYPE_ACK_TMR;
  		llc_station_state_process(skb);
  	}
  }
  
  /*
   *	llc_station_rcv - send received pdu to the station state machine
   *	@skb: received frame.
   *
   *	Sends data unit to station state machine.
   */
  static void llc_station_rcv(struct sk_buff *skb)
  {
  	struct llc_station_state_ev *ev = llc_station_ev(skb);
  
  	ev->type   = LLC_STATION_EV_TYPE_PDU;
  	ev->reason = 0;
  	llc_station_state_process(skb);
  }
  
  int __init llc_station_init(void)
  {

  	int rc = -ENOBUFS;

  	struct sk_buff *skb;
  	struct llc_station_state_ev *ev;
  
  	skb_queue_head_init(&llc_main_station.mac_pdu_q);
  	skb_queue_head_init(&llc_main_station.ev_q.list);
  	spin_lock_init(&llc_main_station.ev_q.lock);

  	setup_timer(&llc_main_station.ack_timer, llc_station_ack_tmr_cb,
  			(unsigned long)&llc_main_station);

  	llc_main_station.ack_timer.expires  = jiffies +
  						sysctl_llc_station_ack_timeout;

  	skb = alloc_skb(0, GFP_ATOMIC);
  	if (!skb)
  		goto out;
  	rc = 0;
  	llc_set_station_handler(llc_station_rcv);
  	ev = llc_station_ev(skb);
  	memset(ev, 0, sizeof(*ev));

  	llc_main_station.maximum_retry	= 1;
  	llc_main_station.state		= LLC_STATION_STATE_DOWN;
  	ev->type	= LLC_STATION_EV_TYPE_SIMPLE;
  	ev->prim_type	= LLC_STATION_EV_ENABLE_WITHOUT_DUP_ADDR_CHECK;
  	rc = llc_station_next_state(skb);
  out:
  	return rc;
  }
  
  void __exit llc_station_exit(void)
  {
  	llc_set_station_handler(NULL);
  }