text: /*
   * net/dst.h	Protocol independent destination cache definitions.
   *
   * Authors:	Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
   *
   */
  
  #ifndef _NET_DST_H
  #define _NET_DST_H
  
  #include <net/dst_ops.h>
  #include <linux/netdevice.h>
  #include <linux/rtnetlink.h>
  #include <linux/rcupdate.h>
  #include <linux/bug.h>
  #include <linux/jiffies.h>
  #include <net/neighbour.h>
  #include <asm/processor.h>
  
  #define DST_GC_MIN	(HZ/10)
  #define DST_GC_INC	(HZ/2)
  #define DST_GC_MAX	(120*HZ)
  
  /* Each dst_entry has reference count and sits in some parent list(s).
   * When it is removed from parent list, it is "freed" (dst_free).
   * After this it enters dead state (dst->obsolete > 0) and if its refcnt
   * is zero, it can be destroyed immediately, otherwise it is added
   * to gc list and garbage collector periodically checks the refcnt.
   */
  
  struct sk_buff;
  
  struct dst_entry {
  	struct rcu_head		rcu_head;
  	struct dst_entry	*child;
  	struct net_device       *dev;
  	struct  dst_ops	        *ops;
  	unsigned long		_metrics;
  	unsigned long           expires;
  	struct dst_entry	*path;
  	struct dst_entry	*from;
  #ifdef CONFIG_XFRM
  	struct xfrm_state	*xfrm;
  #else
  	void			*__pad1;
  #endif
  	int			(*input)(struct sk_buff *);
  	int			(*output)(struct sk_buff *);
  
  	unsigned short		flags;
  #define DST_HOST		0x0001
  #define DST_NOXFRM		0x0002
  #define DST_NOPOLICY		0x0004
  #define DST_NOHASH		0x0008
  #define DST_NOCACHE		0x0010
  #define DST_NOCOUNT		0x0020
  #define DST_NOPEER		0x0040
  #define DST_FAKE_RTABLE		0x0080
  #define DST_XFRM_TUNNEL		0x0100
  #define DST_XFRM_QUEUE		0x0200
  
  	unsigned short		pending_confirm;
  
  	short			error;
  
  	/* A non-zero value of dst->obsolete forces by-hand validation
  	 * of the route entry.  Positive values are set by the generic
  	 * dst layer to indicate that the entry has been forcefully
  	 * destroyed.
  	 *
  	 * Negative values are used by the implementation layer code to
  	 * force invocation of the dst_ops->check() method.
  	 */
  	short			obsolete;
  #define DST_OBSOLETE_NONE	0
  #define DST_OBSOLETE_DEAD	2
  #define DST_OBSOLETE_FORCE_CHK	-1
  #define DST_OBSOLETE_KILL	-2
  	unsigned short		header_len;	/* more space at head required */
  	unsigned short		trailer_len;	/* space to reserve at tail */
  #ifdef CONFIG_IP_ROUTE_CLASSID
  	__u32			tclassid;
  #else
  	__u32			__pad2;
  #endif
  
  	/*
  	 * Align __refcnt to a 64 bytes alignment
  	 * (L1_CACHE_SIZE would be too much)
  	 */
  #ifdef CONFIG_64BIT
  	long			__pad_to_align_refcnt[2];
  #endif
  	/*
  	 * __refcnt wants to be on a different cache line from
  	 * input/output/ops or performance tanks badly
  	 */
  	atomic_t		__refcnt;	/* client references	*/
  	int			__use;
  	unsigned long		lastuse;
  	union {
  		struct dst_entry	*next;
  		struct rtable __rcu	*rt_next;
  		struct rt6_info		*rt6_next;
  		struct dn_route __rcu	*dn_next;
  	};
  };
  
  u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old);
  extern const u32 dst_default_metrics[];
  
  #define DST_METRICS_READ_ONLY	0x1UL
  #define __DST_METRICS_PTR(Y)	\
  	((u32 *)((Y) & ~DST_METRICS_READ_ONLY))
  #define DST_METRICS_PTR(X)	__DST_METRICS_PTR((X)->_metrics)
  
  static inline bool dst_metrics_read_only(const struct dst_entry *dst)
  {
  	return dst->_metrics & DST_METRICS_READ_ONLY;
  }
  
  void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old);
  
  static inline void dst_destroy_metrics_generic(struct dst_entry *dst)
  {
  	unsigned long val = dst->_metrics;
  	if (!(val & DST_METRICS_READ_ONLY))
  		__dst_destroy_metrics_generic(dst, val);
  }
  
  static inline u32 *dst_metrics_write_ptr(struct dst_entry *dst)
  {
  	unsigned long p = dst->_metrics;
  
  	BUG_ON(!p);
  
  	if (p & DST_METRICS_READ_ONLY)
  		return dst->ops->cow_metrics(dst, p);
  	return __DST_METRICS_PTR(p);
  }
  
  /* This may only be invoked before the entry has reached global
   * visibility.
   */
  static inline void dst_init_metrics(struct dst_entry *dst,
  				    const u32 *src_metrics,
  				    bool read_only)
  {
  	dst->_metrics = ((unsigned long) src_metrics) |
  		(read_only ? DST_METRICS_READ_ONLY : 0);
  }
  
  static inline void dst_copy_metrics(struct dst_entry *dest, const struct dst_entry *src)
  {
  	u32 *dst_metrics = dst_metrics_write_ptr(dest);
  
  	if (dst_metrics) {
  		u32 *src_metrics = DST_METRICS_PTR(src);
  
  		memcpy(dst_metrics, src_metrics, RTAX_MAX * sizeof(u32));
  	}
  }
  
  static inline u32 *dst_metrics_ptr(struct dst_entry *dst)
  {
  	return DST_METRICS_PTR(dst);
  }
  
  static inline u32
  dst_metric_raw(const struct dst_entry *dst, const int metric)
  {
  	u32 *p = DST_METRICS_PTR(dst);
  
  	return p[metric-1];
  }
  
  static inline u32
  dst_metric(const struct dst_entry *dst, const int metric)
  {
  	WARN_ON_ONCE(metric == RTAX_HOPLIMIT ||
  		     metric == RTAX_ADVMSS ||
  		     metric == RTAX_MTU);
  	return dst_metric_raw(dst, metric);
  }
  
  static inline u32
  dst_metric_advmss(const struct dst_entry *dst)
  {
  	u32 advmss = dst_metric_raw(dst, RTAX_ADVMSS);
  
  	if (!advmss)
  		advmss = dst->ops->default_advmss(dst);
  
  	return advmss;
  }
  
  static inline void dst_metric_set(struct dst_entry *dst, int metric, u32 val)
  {
  	u32 *p = dst_metrics_write_ptr(dst);
  
  	if (p)
  		p[metric-1] = val;
  }
  
  static inline u32
  dst_feature(const struct dst_entry *dst, u32 feature)
  {
  	return dst_metric(dst, RTAX_FEATURES) & feature;
  }
  
  static inline u32 dst_mtu(const struct dst_entry *dst)
  {
  	return dst->ops->mtu(dst);
  }
  
  /* RTT metrics are stored in milliseconds for user ABI, but used as jiffies */
  static inline unsigned long dst_metric_rtt(const struct dst_entry *dst, int metric)
  {
  	return msecs_to_jiffies(dst_metric(dst, metric));
  }
  
  static inline u32
  dst_allfrag(const struct dst_entry *dst)
  {
  	int ret = dst_feature(dst,  RTAX_FEATURE_ALLFRAG);
  	return ret;
  }
  
  static inline int
  dst_metric_locked(const struct dst_entry *dst, int metric)
  {
  	return dst_metric(dst, RTAX_LOCK) & (1<<metric);
  }
  
  static inline void dst_hold(struct dst_entry *dst)
  {
  	/*
  	 * If your kernel compilation stops here, please check
  	 * __pad_to_align_refcnt declaration in struct dst_entry
  	 */
  	BUILD_BUG_ON(offsetof(struct dst_entry, __refcnt) & 63);
  	atomic_inc(&dst->__refcnt);
  }
  
  static inline void dst_use(struct dst_entry *dst, unsigned long time)
  {
  	dst_hold(dst);
  	dst->__use++;
  	dst->lastuse = time;
  }
  
  static inline void dst_use_noref(struct dst_entry *dst, unsigned long time)
  {
  	dst->__use++;
  	dst->lastuse = time;
  }
  
  static inline struct dst_entry *dst_clone(struct dst_entry *dst)
  {
  	if (dst)
  		atomic_inc(&dst->__refcnt);
  	return dst;
  }
  
  void dst_release(struct dst_entry *dst);
  
  static inline void refdst_drop(unsigned long refdst)
  {
  	if (!(refdst & SKB_DST_NOREF))
  		dst_release((struct dst_entry *)(refdst & SKB_DST_PTRMASK));
  }
  
  /**
   * skb_dst_drop - drops skb dst
   * @skb: buffer
   *
   * Drops dst reference count if a reference was taken.
   */
  static inline void skb_dst_drop(struct sk_buff *skb)
  {
  	if (skb->_skb_refdst) {
  		refdst_drop(skb->_skb_refdst);
  		skb->_skb_refdst = 0UL;
  	}
  }
  
  static inline void skb_dst_copy(struct sk_buff *nskb, const struct sk_buff *oskb)
  {
  	nskb->_skb_refdst = oskb->_skb_refdst;
  	if (!(nskb->_skb_refdst & SKB_DST_NOREF))
  		dst_clone(skb_dst(nskb));
  }
  
  /**
   * skb_dst_force - makes sure skb dst is refcounted
   * @skb: buffer
   *
   * If dst is not yet refcounted, let's do it
   */
  static inline void skb_dst_force(struct sk_buff *skb)
  {
  	if (skb_dst_is_noref(skb)) {
  		WARN_ON(!rcu_read_lock_held());
  		skb->_skb_refdst &= ~SKB_DST_NOREF;
  		dst_clone(skb_dst(skb));
  	}
  }
  
  
  /**
   *	__skb_tunnel_rx - prepare skb for rx reinsert
   *	@skb: buffer
   *	@dev: tunnel device
   *	@net: netns for packet i/o
   *
   *	After decapsulation, packet is going to re-enter (netif_rx()) our stack,
   *	so make some cleanups. (no accounting done)
   */
  static inline void __skb_tunnel_rx(struct sk_buff *skb, struct net_device *dev,
  				   struct net *net)
  {
  	skb->dev = dev;
  
  	/*
  	 * Clear rxhash so that we can recalulate the hash for the
  	 * encapsulated packet, unless we have already determine the hash
  	 * over the L4 4-tuple.
  	 */
  	if (!skb->l4_rxhash)
  		skb->rxhash = 0;
  	skb_set_queue_mapping(skb, 0);
  	skb_scrub_packet(skb, !net_eq(net, dev_net(dev)));
  }
  
  /**
   *	skb_tunnel_rx - prepare skb for rx reinsert
   *	@skb: buffer
   *	@dev: tunnel device
   *
   *	After decapsulation, packet is going to re-enter (netif_rx()) our stack,
   *	so make some cleanups, and perform accounting.
   *	Note: this accounting is not SMP safe.
   */
  static inline void skb_tunnel_rx(struct sk_buff *skb, struct net_device *dev,
  				 struct net *net)
  {
  	/* TODO : stats should be SMP safe */
  	dev->stats.rx_packets++;
  	dev->stats.rx_bytes += skb->len;
  	__skb_tunnel_rx(skb, dev, net);
  }
  
  /* Children define the path of the packet through the
   * Linux networking.  Thus, destinations are stackable.
   */
  
  static inline struct dst_entry *skb_dst_pop(struct sk_buff *skb)
  {
  	struct dst_entry *child = dst_clone(skb_dst(skb)->child);
  
  	skb_dst_drop(skb);
  	return child;
  }
  
  int dst_discard(struct sk_buff *skb);
  void *dst_alloc(struct dst_ops *ops, struct net_device *dev, int initial_ref,
  		int initial_obsolete, unsigned short flags);
  void __dst_free(struct dst_entry *dst);
  struct dst_entry *dst_destroy(struct dst_entry *dst);
  
  static inline void dst_free(struct dst_entry *dst)
  {
  	if (dst->obsolete > 0)
  		return;
  	if (!atomic_read(&dst->__refcnt)) {
  		dst = dst_destroy(dst);
  		if (!dst)
  			return;
  	}
  	__dst_free(dst);
  }
  
  static inline void dst_rcu_free(struct rcu_head *head)
  {
  	struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
  	dst_free(dst);
  }
  
  static inline void dst_confirm(struct dst_entry *dst)
  {
  	dst->pending_confirm = 1;
  }
  
  static inline int dst_neigh_output(struct dst_entry *dst, struct neighbour *n,
  				   struct sk_buff *skb)
  {
  	const struct hh_cache *hh;
  
  	if (dst->pending_confirm) {
  		unsigned long now = jiffies;
  
  		dst->pending_confirm = 0;
  		/* avoid dirtying neighbour */
  		if (n->confirmed != now)
  			n->confirmed = now;
  	}
  
  	hh = &n->hh;
  	if ((n->nud_state & NUD_CONNECTED) && hh->hh_len)
  		return neigh_hh_output(hh, skb);
  	else
  		return n->output(n, skb);
  }
  
  static inline struct neighbour *dst_neigh_lookup(const struct dst_entry *dst, const void *daddr)
  {
  	struct neighbour *n = dst->ops->neigh_lookup(dst, NULL, daddr);
  	return IS_ERR(n) ? NULL : n;
  }
  
  static inline struct neighbour *dst_neigh_lookup_skb(const struct dst_entry *dst,
  						     struct sk_buff *skb)
  {
  	struct neighbour *n =  dst->ops->neigh_lookup(dst, skb, NULL);
  	return IS_ERR(n) ? NULL : n;
  }
  
  static inline void dst_link_failure(struct sk_buff *skb)
  {
  	struct dst_entry *dst = skb_dst(skb);
  	if (dst && dst->ops && dst->ops->link_failure)
  		dst->ops->link_failure(skb);
  }
  
  static inline void dst_set_expires(struct dst_entry *dst, int timeout)
  {
  	unsigned long expires = jiffies + timeout;
  
  	if (expires == 0)
  		expires = 1;
  
  	if (dst->expires == 0 || time_before(expires, dst->expires))
  		dst->expires = expires;
  }
  
  /* Output packet to network from transport.  */
  static inline int dst_output(struct sk_buff *skb)
  {
  	return skb_dst(skb)->output(skb);
  }
  
  /* Input packet from network to transport.  */
  static inline int dst_input(struct sk_buff *skb)
  {
  	return skb_dst(skb)->input(skb);
  }
  
  static inline struct dst_entry *dst_check(struct dst_entry *dst, u32 cookie)
  {
  	if (dst->obsolete)
  		dst = dst->ops->check(dst, cookie);
  	return dst;
  }
  
  void dst_init(void);
  
  /* Flags for xfrm_lookup flags argument. */
  enum {
  	XFRM_LOOKUP_ICMP = 1 << 0,
  };
  
  struct flowi;
  #ifndef CONFIG_XFRM
  static inline struct dst_entry *xfrm_lookup(struct net *net,
  					    struct dst_entry *dst_orig,
  					    const struct flowi *fl, struct sock *sk,
  					    int flags)
  {
  	return dst_orig;
  } 
  
  static inline struct xfrm_state *dst_xfrm(const struct dst_entry *dst)
  {
  	return NULL;
  }
  
  #else
  struct dst_entry *xfrm_lookup(struct net *net, struct dst_entry *dst_orig,
  			      const struct flowi *fl, struct sock *sk,
  			      int flags);
  
  /* skb attached with this dst needs transformation if dst->xfrm is valid */
  static inline struct xfrm_state *dst_xfrm(const struct dst_entry *dst)
  {
  	return dst->xfrm;
  }
  #endif
  
  #endif /* _NET_DST_H */
  