/*
   * llc_input.c - Minimal input path for 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/netdevice.h>
  #include <linux/slab.h>
  #include <linux/export.h>
  #include <net/net_namespace.h>
  #include <net/llc.h>
  #include <net/llc_pdu.h>
  #include <net/llc_sap.h>
  
  #if 0
  #define dprintk(args...) printk(KERN_DEBUG args)
  #else
  #define dprintk(args...)
  #endif
  
  /*
   * Packet handler for the station, registerable because in the minimal
   * LLC core that is taking shape only the very minimal subset of LLC that
   * is needed for things like IPX, Appletalk, etc will stay, with all the
   * rest in the llc1 and llc2 modules.
   */
  static void (*llc_station_handler)(struct sk_buff *skb);
  
  /*
   * Packet handlers for LLC_DEST_SAP and LLC_DEST_CONN.
   */
  static void (*llc_type_handlers[2])(struct llc_sap *sap,
  				    struct sk_buff *skb);
  
  void llc_add_pack(int type, void (*handler)(struct llc_sap *sap,
  					    struct sk_buff *skb))
  {
  	smp_wmb(); /* ensure initialisation is complete before it's called */
  	if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
  		llc_type_handlers[type - 1] = handler;
  }
  
  void llc_remove_pack(int type)
  {
  	if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
  		llc_type_handlers[type - 1] = NULL;
  	synchronize_net();
  }
  
  void llc_set_station_handler(void (*handler)(struct sk_buff *skb))
  {
  	/* Ensure initialisation is complete before it's called */
  	if (handler)
  		smp_wmb();
  
  	llc_station_handler = handler;
  
  	if (!handler)
  		synchronize_net();
  }
  
  /**
   *	llc_pdu_type - returns which LLC component must handle for PDU
   *	@skb: input skb
   *
   *	This function returns which LLC component must handle this PDU.
   */
  static __inline__ int llc_pdu_type(struct sk_buff *skb)
  {
  	int type = LLC_DEST_CONN; /* I-PDU or S-PDU type */
  	struct llc_pdu_sn *pdu = llc_pdu_sn_hdr(skb);
  
  	if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) != LLC_PDU_TYPE_U)
  		goto out;
  	switch (LLC_U_PDU_CMD(pdu)) {
  	case LLC_1_PDU_CMD_XID:
  	case LLC_1_PDU_CMD_UI:
  	case LLC_1_PDU_CMD_TEST:
  		type = LLC_DEST_SAP;
  		break;
  	case LLC_2_PDU_CMD_SABME:
  	case LLC_2_PDU_CMD_DISC:
  	case LLC_2_PDU_RSP_UA:
  	case LLC_2_PDU_RSP_DM:
  	case LLC_2_PDU_RSP_FRMR:
  		break;
  	default:
  		type = LLC_DEST_INVALID;
  		break;
  	}
  out:
  	return type;
  }
  
  /**
   *	llc_fixup_skb - initializes skb pointers
   *	@skb: This argument points to incoming skb
   *
   *	Initializes internal skb pointer to start of network layer by deriving
   *	length of LLC header; finds length of LLC control field in LLC header
   *	by looking at the two lowest-order bits of the first control field
   *	byte; field is either 3 or 4 bytes long.
   */
  static inline int llc_fixup_skb(struct sk_buff *skb)
  {
  	u8 llc_len = 2;
  	struct llc_pdu_un *pdu;
  
  	if (unlikely(!pskb_may_pull(skb, sizeof(*pdu))))
  		return 0;
  
  	pdu = (struct llc_pdu_un *)skb->data;
  	if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) == LLC_PDU_TYPE_U)
  		llc_len = 1;
  	llc_len += 2;
  
  	if (unlikely(!pskb_may_pull(skb, llc_len)))
  		return 0;
  
  	skb->transport_header += llc_len;
  	skb_pull(skb, llc_len);
  	if (skb->protocol == htons(ETH_P_802_2)) {
  		__be16 pdulen = eth_hdr(skb)->h_proto;
  		s32 data_size = ntohs(pdulen) - llc_len;
  
  		if (data_size < 0 ||
  		    !pskb_may_pull(skb, data_size))
  			return 0;
  		if (unlikely(pskb_trim_rcsum(skb, data_size)))
  			return 0;
  	}
  	return 1;
  }
  
  /**
   *	llc_rcv - 802.2 entry point from net lower layers
   *	@skb: received pdu
   *	@dev: device that receive pdu
   *	@pt: packet type
   *
   *	When the system receives a 802.2 frame this function is called. It
   *	checks SAP and connection of received pdu and passes frame to
   *	llc_{station,sap,conn}_rcv for sending to proper state machine. If
   *	the frame is related to a busy connection (a connection is sending
   *	data now), it queues this frame in the connection's backlog.
   */
  int llc_rcv(struct sk_buff *skb, struct net_device *dev,
  	    struct packet_type *pt, struct net_device *orig_dev)
  {
  	struct llc_sap *sap;
  	struct llc_pdu_sn *pdu;
  	int dest;
  	int (*rcv)(struct sk_buff *, struct net_device *,
  		   struct packet_type *, struct net_device *);
  	void (*sta_handler)(struct sk_buff *skb);
  	void (*sap_handler)(struct llc_sap *sap, struct sk_buff *skb);
  
  	if (!net_eq(dev_net(dev), &init_net))
  		goto drop;
  
  	/*
  	 * When the interface is in promisc. mode, drop all the crap that it
  	 * receives, do not try to analyse it.
  	 */
  	if (unlikely(skb->pkt_type == PACKET_OTHERHOST)) {
  		dprintk("%s: PACKET_OTHERHOST
  ", __func__);
  		goto drop;
  	}
  	skb = skb_share_check(skb, GFP_ATOMIC);
  	if (unlikely(!skb))
  		goto out;
  	if (unlikely(!llc_fixup_skb(skb)))
  		goto drop;
  	pdu = llc_pdu_sn_hdr(skb);
  	if (unlikely(!pdu->dsap)) /* NULL DSAP, refer to station */
  	       goto handle_station;
  	sap = llc_sap_find(pdu->dsap);
  	if (unlikely(!sap)) {/* unknown SAP */
  		dprintk("%s: llc_sap_find(%02X) failed!
  ", __func__,
  			pdu->dsap);
  		goto drop;
  	}
  	/*
  	 * First the upper layer protocols that don't need the full
  	 * LLC functionality
  	 */
  	rcv = rcu_dereference(sap->rcv_func);
  	dest = llc_pdu_type(skb);
  	sap_handler = dest ? ACCESS_ONCE(llc_type_handlers[dest - 1]) : NULL;
  	if (unlikely(!sap_handler)) {
  		if (rcv)
  			rcv(skb, dev, pt, orig_dev);
  		else
  			kfree_skb(skb);
  	} else {
  		if (rcv) {
  			struct sk_buff *cskb = skb_clone(skb, GFP_ATOMIC);
  			if (cskb)
  				rcv(cskb, dev, pt, orig_dev);
  		}
  		sap_handler(sap, skb);
  	}
  	llc_sap_put(sap);
  out:
  	return 0;
  drop:
  	kfree_skb(skb);
  	goto out;
  handle_station:
  	sta_handler = ACCESS_ONCE(llc_station_handler);
  	if (!sta_handler)
  		goto drop;
  	sta_handler(skb);
  	goto out;
  }
  
  EXPORT_SYMBOL(llc_add_pack);
  EXPORT_SYMBOL(llc_remove_pack);
  EXPORT_SYMBOL(llc_set_station_handler);