text: /*
   *	Definitions for the 'struct sk_buff' memory handlers.
   *
   *	Authors:
   *		Alan Cox, <gw4pts@gw4pts.ampr.org>
   *		Florian La Roche, <rzsfl@rz.uni-sb.de>
   *
   *	This program is free software; you can redistribute it and/or
   *	modify it under the terms of the GNU General Public License
   *	as published by the Free Software Foundation; either version
   *	2 of the License, or (at your option) any later version.
   */
  
  #ifndef _LINUX_SKBUFF_H
  #define _LINUX_SKBUFF_H
  
  #include <linux/config.h>
  #include <linux/kernel.h>
  #include <linux/compiler.h>
  #include <linux/time.h>
  #include <linux/cache.h>
  
  #include <asm/atomic.h>
  #include <asm/types.h>
  #include <linux/spinlock.h>
  #include <linux/mm.h>
  #include <linux/highmem.h>
  #include <linux/poll.h>
  #include <linux/net.h>
  
  #define HAVE_ALLOC_SKB		/* For the drivers to know */
  #define HAVE_ALIGNABLE_SKB	/* Ditto 8)		   */
  #define SLAB_SKB 		/* Slabified skbuffs 	   */
  
  #define CHECKSUM_NONE 0
  #define CHECKSUM_HW 1
  #define CHECKSUM_UNNECESSARY 2
  
  #define SKB_DATA_ALIGN(X)	(((X) + (SMP_CACHE_BYTES - 1)) & \
  				 ~(SMP_CACHE_BYTES - 1))
  #define SKB_MAX_ORDER(X, ORDER)	(((PAGE_SIZE << (ORDER)) - (X) - \
  				  sizeof(struct skb_shared_info)) & \
  				  ~(SMP_CACHE_BYTES - 1))
  #define SKB_MAX_HEAD(X)		(SKB_MAX_ORDER((X), 0))
  #define SKB_MAX_ALLOC		(SKB_MAX_ORDER(0, 2))
  
  /* A. Checksumming of received packets by device.
   *
   *	NONE: device failed to checksum this packet.
   *		skb->csum is undefined.
   *
   *	UNNECESSARY: device parsed packet and wouldbe verified checksum.
   *		skb->csum is undefined.
   *	      It is bad option, but, unfortunately, many of vendors do this.
   *	      Apparently with secret goal to sell you new device, when you
   *	      will add new protocol to your host. F.e. IPv6. 8)
   *
   *	HW: the most generic way. Device supplied checksum of _all_
   *	    the packet as seen by netif_rx in skb->csum.
   *	    NOTE: Even if device supports only some protocols, but
   *	    is able to produce some skb->csum, it MUST use HW,
   *	    not UNNECESSARY.
   *
   * B. Checksumming on output.
   *
   *	NONE: skb is checksummed by protocol or csum is not required.
   *
   *	HW: device is required to csum packet as seen by hard_start_xmit
   *	from skb->h.raw to the end and to record the checksum
   *	at skb->h.raw+skb->csum.
   *
   *	Device must show its capabilities in dev->features, set
   *	at device setup time.
   *	NETIF_F_HW_CSUM	- it is clever device, it is able to checksum
   *			  everything.
   *	NETIF_F_NO_CSUM - loopback or reliable single hop media.
   *	NETIF_F_IP_CSUM - device is dumb. It is able to csum only
   *			  TCP/UDP over IPv4. Sigh. Vendors like this
   *			  way by an unknown reason. Though, see comment above
   *			  about CHECKSUM_UNNECESSARY. 8)
   *
   *	Any questions? No questions, good. 		--ANK
   */
  
  #ifdef __i386__
  #define NET_CALLER(arg) (*(((void **)&arg) - 1))
  #else
  #define NET_CALLER(arg) __builtin_return_address(0)
  #endif
  
  #ifdef CONFIG_NETFILTER
  struct nf_conntrack {
  	atomic_t use;
  	void (*destroy)(struct nf_conntrack *);
  };
  
  struct nf_ct_info {
  	struct nf_conntrack *master;
  };
  
  #ifdef CONFIG_BRIDGE_NETFILTER
  struct nf_bridge_info {
  	atomic_t use;
  	struct net_device *physindev;
  	struct net_device *physoutdev;
  #if defined(CONFIG_VLAN_8021Q) || defined(CONFIG_VLAN_8021Q_MODULE)
  	struct net_device *netoutdev;
  #endif
  	unsigned int mask;
  	unsigned long hh[32 / sizeof(unsigned long)];
  };
  #endif
  
  #endif
  
  struct sk_buff_head {
  	/* These two members must be first. */
  	struct sk_buff	*next;
  	struct sk_buff	*prev;
  
  	__u32		qlen;
  	spinlock_t	lock;
  };
  
  struct sk_buff;
  
  /* To allow 64K frame to be packed as single skb without frag_list */
  #define MAX_SKB_FRAGS (65536/PAGE_SIZE + 2)
  
  typedef struct skb_frag_struct skb_frag_t;
  
  struct skb_frag_struct {
  	struct page *page;
  	__u16 page_offset;
  	__u16 size;
  };
  
  /* This data is invariant across clones and lives at
   * the end of the header data, ie. at skb->end.
   */
  struct skb_shared_info {
  	atomic_t	dataref;
  	unsigned int	nr_frags;
  	unsigned short	tso_size;
  	unsigned short	tso_segs;
  	struct sk_buff	*frag_list;
  	skb_frag_t	frags[MAX_SKB_FRAGS];
  };
  
  /** 
   *	struct sk_buff - socket buffer
   *	@next: Next buffer in list
   *	@prev: Previous buffer in list
   *	@list: List we are on
   *	@sk: Socket we are owned by
   *	@stamp: Time we arrived
   *	@dev: Device we arrived on/are leaving by
   *      @real_dev: The real device we are using
   *	@h: Transport layer header
   *	@nh: Network layer header
   *	@mac: Link layer header
   *	@dst: FIXME: Describe this field
   *	@cb: Control buffer. Free for use by every layer. Put private vars here
   *	@len: Length of actual data
   *	@data_len: Data length
   *	@csum: Checksum
   *	@__unused: Dead field, may be reused
   *	@cloned: Head may be cloned (check refcnt to be sure)
   *	@pkt_type: Packet class
   *	@ip_summed: Driver fed us an IP checksum
   *	@priority: Packet queueing priority
   *	@users: User count - see {datagram,tcp}.c
   *	@protocol: Packet protocol from driver
   *	@security: Security level of packet
   *	@truesize: Buffer size 
   *	@head: Head of buffer
   *	@data: Data head pointer
   *	@tail: Tail pointer
   *	@end: End pointer
   *	@destructor: Destruct function
   *	@nfmark: Can be used for communication between hooks
   *	@nfcache: Cache info
   *	@nfct: Associated connection, if any
   *	@nf_debug: Netfilter debugging
   *	@nf_bridge: Saved data about a bridged frame - see br_netfilter.c
   *      @private: Data which is private to the HIPPI implementation
   *	@tc_index: Traffic control index
   */
  
  struct sk_buff {
  	/* These two members must be first. */
  	struct sk_buff		*next;
  	struct sk_buff		*prev;
  
  	struct sk_buff_head	*list;
  	struct sock		*sk;
  	struct timeval		stamp;
  	struct net_device	*dev;
  	struct net_device	*real_dev;
  
  	union {
  		struct tcphdr	*th;
  		struct udphdr	*uh;
  		struct icmphdr	*icmph;
  		struct igmphdr	*igmph;
  		struct iphdr	*ipiph;
  		unsigned char	*raw;
  	} h;
  
  	union {
  		struct iphdr	*iph;
  		struct ipv6hdr	*ipv6h;
  		struct arphdr	*arph;
  		unsigned char	*raw;
  	} nh;
  
  	union {
  	  	struct ethhdr	*ethernet;
  	  	unsigned char 	*raw;
  	} mac;
  
  	struct  dst_entry	*dst;
  	struct	sec_path	*sp;
  
  	/*
  	 * This is the control buffer. It is free to use for every
  	 * layer. Please put your private variables there. If you
  	 * want to keep them across layers you have to do a skb_clone()
  	 * first. This is owned by whoever has the skb queued ATM.
  	 */
  	char			cb[48];
  
  	unsigned int		len,
  				data_len,
  				csum;
  	unsigned char		local_df,
  				cloned,
  				pkt_type,
  				ip_summed;
  	__u32			priority;
  	unsigned short		protocol,
  				security;
  
  	void			(*destructor)(struct sk_buff *skb);
  #ifdef CONFIG_NETFILTER
          unsigned long		nfmark;
  	__u32			nfcache;
  	struct nf_ct_info	*nfct;
  #ifdef CONFIG_NETFILTER_DEBUG
          unsigned int		nf_debug;
  #endif
  #ifdef CONFIG_BRIDGE_NETFILTER
  	struct nf_bridge_info	*nf_bridge;
  #endif
  #endif /* CONFIG_NETFILTER */
  #if defined(CONFIG_HIPPI)
  	union {
  		__u32		ifield;
  	} private;
  #endif
  #ifdef CONFIG_NET_SCHED
         __u32			tc_index;               /* traffic control index */
  #endif
  
  	/* These elements must be at the end, see alloc_skb() for details.  */
  	unsigned int		truesize;
  	atomic_t		users;
  	unsigned char		*head,
  				*data,
  				*tail,
  				*end;
  };
  
  #define SK_WMEM_MAX	65535
  #define SK_RMEM_MAX	65535
  
  #ifdef __KERNEL__
  /*
   *	Handling routines are only of interest to the kernel
   */
  #include <linux/slab.h>
  
  #include <asm/system.h>
  
  extern void	       __kfree_skb(struct sk_buff *skb);
  extern struct sk_buff *alloc_skb(unsigned int size, int priority);
  extern void	       kfree_skbmem(struct sk_buff *skb);
  extern struct sk_buff *skb_clone(struct sk_buff *skb, int priority);
  extern struct sk_buff *skb_copy(const struct sk_buff *skb, int priority);
  extern struct sk_buff *pskb_copy(struct sk_buff *skb, int gfp_mask);
  extern int	       pskb_expand_head(struct sk_buff *skb,
  					int nhead, int ntail, int gfp_mask);
  extern struct sk_buff *skb_realloc_headroom(struct sk_buff *skb,
  					    unsigned int headroom);
  extern struct sk_buff *skb_copy_expand(const struct sk_buff *skb,
  				       int newheadroom, int newtailroom,
  				       int priority);
  extern struct sk_buff *		skb_pad(struct sk_buff *skb, int pad);
  #define dev_kfree_skb(a)	kfree_skb(a)
  extern void	      skb_over_panic(struct sk_buff *skb, int len,
  				     void *here);
  extern void	      skb_under_panic(struct sk_buff *skb, int len,
  				      void *here);
  
  /* Internal */
  #define skb_shinfo(SKB)		((struct skb_shared_info *)((SKB)->end))
  
  /**
   *	skb_queue_empty - check if a queue is empty
   *	@list: queue head
   *
   *	Returns true if the queue is empty, false otherwise.
   */
  static inline int skb_queue_empty(const struct sk_buff_head *list)
  {
  	return list->next == (struct sk_buff *)list;
  }
  
  /**
   *	skb_get - reference buffer
   *	@skb: buffer to reference
   *
   *	Makes another reference to a socket buffer and returns a pointer
   *	to the buffer.
   */
  static inline struct sk_buff *skb_get(struct sk_buff *skb)
  {
  	atomic_inc(&skb->users);
  	return skb;
  }
  
  /*
   * If users == 1, we are the only owner and are can avoid redundant
   * atomic change.
   */
  
  /**
   *	kfree_skb - free an sk_buff
   *	@skb: buffer to free
   *
   *	Drop a reference to the buffer and free it if the usage count has
   *	hit zero.
   */
  static inline void kfree_skb(struct sk_buff *skb)
  {
  	if (atomic_read(&skb->users) == 1 || atomic_dec_and_test(&skb->users))
  		__kfree_skb(skb);
  }
  
  /* Use this if you didn't touch the skb state [for fast switching] */
  static inline void kfree_skb_fast(struct sk_buff *skb)
  {
  	if (atomic_read(&skb->users) == 1 || atomic_dec_and_test(&skb->users))
  		kfree_skbmem(skb);
  }
  
  /**
   *	skb_cloned - is the buffer a clone
   *	@skb: buffer to check
   *
   *	Returns true if the buffer was generated with skb_clone() and is
   *	one of multiple shared copies of the buffer. Cloned buffers are
   *	shared data so must not be written to under normal circumstances.
   */
  static inline int skb_cloned(const struct sk_buff *skb)
  {
  	return skb->cloned && atomic_read(&skb_shinfo(skb)->dataref) != 1;
  }
  
  /**
   *	skb_shared - is the buffer shared
   *	@skb: buffer to check
   *
   *	Returns true if more than one person has a reference to this
   *	buffer.
   */
  static inline int skb_shared(const struct sk_buff *skb)
  {
  	return atomic_read(&skb->users) != 1;
  }
  
  /**
   *	skb_share_check - check if buffer is shared and if so clone it
   *	@skb: buffer to check
   *	@pri: priority for memory allocation
   *
   *	If the buffer is shared the buffer is cloned and the old copy
   *	drops a reference. A new clone with a single reference is returned.
   *	If the buffer is not shared the original buffer is returned. When
   *	being called from interrupt status or with spinlocks held pri must
   *	be GFP_ATOMIC.
   *
   *	NULL is returned on a memory allocation failure.
   */
  static inline struct sk_buff *skb_share_check(struct sk_buff *skb, int pri)
  {
  	might_sleep_if(pri & __GFP_WAIT);
  	if (skb_shared(skb)) {
  		struct sk_buff *nskb = skb_clone(skb, pri);
  		kfree_skb(skb);
  		skb = nskb;
  	}
  	return skb;
  }
  
  /*
   *	Copy shared buffers into a new sk_buff. We effectively do COW on
   *	packets to handle cases where we have a local reader and forward
   *	and a couple of other messy ones. The normal one is tcpdumping
   *	a packet thats being forwarded.
   */
  
  /**
   *	skb_unshare - make a copy of a shared buffer
   *	@skb: buffer to check
   *	@pri: priority for memory allocation
   *
   *	If the socket buffer is a clone then this function creates a new
   *	copy of the data, drops a reference count on the old copy and returns
   *	the new copy with the reference count at 1. If the buffer is not a clone
   *	the original buffer is returned. When called with a spinlock held or
   *	from interrupt state @pri must be %GFP_ATOMIC
   *
   *	%NULL is returned on a memory allocation failure.
   */
  static inline struct sk_buff *skb_unshare(struct sk_buff *skb, int pri)
  {
  	might_sleep_if(pri & __GFP_WAIT);
  	if (skb_cloned(skb)) {
  		struct sk_buff *nskb = skb_copy(skb, pri);
  		kfree_skb(skb);	/* Free our shared copy */
  		skb = nskb;
  	}
  	return skb;
  }
  
  /**
   *	skb_peek
   *	@list_: list to peek at
   *
   *	Peek an &sk_buff. Unlike most other operations you _MUST_
   *	be careful with this one. A peek leaves the buffer on the
   *	list and someone else may run off with it. You must hold
   *	the appropriate locks or have a private queue to do this.
   *
   *	Returns %NULL for an empty list or a pointer to the head element.
   *	The reference count is not incremented and the reference is therefore
   *	volatile. Use with caution.
   */
  static inline struct sk_buff *skb_peek(struct sk_buff_head *list_)
  {
  	struct sk_buff *list = ((struct sk_buff *)list_)->next;
  	if (list == (struct sk_buff *)list_)
  		list = NULL;
  	return list;
  }
  
  /**
   *	skb_peek_tail
   *	@list_: list to peek at
   *
   *	Peek an &sk_buff. Unlike most other operations you _MUST_
   *	be careful with this one. A peek leaves the buffer on the
   *	list and someone else may run off with it. You must hold
   *	the appropriate locks or have a private queue to do this.
   *
   *	Returns %NULL for an empty list or a pointer to the tail element.
   *	The reference count is not incremented and the reference is therefore
   *	volatile. Use with caution.
   */
  static inline struct sk_buff *skb_peek_tail(struct sk_buff_head *list_)
  {
  	struct sk_buff *list = ((struct sk_buff *)list_)->prev;
  	if (list == (struct sk_buff *)list_)
  		list = NULL;
  	return list;
  }
  
  /**
   *	skb_queue_len	- get queue length
   *	@list_: list to measure
   *
   *	Return the length of an &sk_buff queue.
   */
  static inline __u32 skb_queue_len(const struct sk_buff_head *list_)
  {
  	return list_->qlen;
  }
  
  static inline void skb_queue_head_init(struct sk_buff_head *list)
  {
  	spin_lock_init(&list->lock);
  	list->prev = list->next = (struct sk_buff *)list;
  	list->qlen = 0;
  }
  
  /*
   *	Insert an sk_buff at the start of a list.
   *
   *	The "__skb_xxxx()" functions are the non-atomic ones that
   *	can only be called with interrupts disabled.
   */
  
  /**
   *	__skb_queue_head - queue a buffer at the list head
   *	@list: list to use
   *	@newsk: buffer to queue
   *
   *	Queue a buffer at the start of a list. This function takes no locks
   *	and you must therefore hold required locks before calling it.
   *
   *	A buffer cannot be placed on two lists at the same time.
   */
  static inline void __skb_queue_head(struct sk_buff_head *list,
  				    struct sk_buff *newsk)
  {
  	struct sk_buff *prev, *next;
  
  	newsk->list = list;
  	list->qlen++;
  	prev = (struct sk_buff *)list;
  	next = prev->next;
  	newsk->next = next;
  	newsk->prev = prev;
  	next->prev  = prev->next = newsk;
  }
  
  
  /**
   *	skb_queue_head - queue a buffer at the list head
   *	@list: list to use
   *	@newsk: buffer to queue
   *
   *	Queue a buffer at the start of the list. This function takes the
   *	list lock and can be used safely with other locking &sk_buff functions
   *	safely.
   *
   *	A buffer cannot be placed on two lists at the same time.
   */
  static inline void skb_queue_head(struct sk_buff_head *list,
  				  struct sk_buff *newsk)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&list->lock, flags);
  	__skb_queue_head(list, newsk);
  	spin_unlock_irqrestore(&list->lock, flags);
  }
  
  /**
   *	__skb_queue_tail - queue a buffer at the list tail
   *	@list: list to use
   *	@newsk: buffer to queue
   *
   *	Queue a buffer at the end of a list. This function takes no locks
   *	and you must therefore hold required locks before calling it.
   *
   *	A buffer cannot be placed on two lists at the same time.
   */
  static inline void __skb_queue_tail(struct sk_buff_head *list,
  				   struct sk_buff *newsk)
  {
  	struct sk_buff *prev, *next;
  
  	newsk->list = list;
  	list->qlen++;
  	next = (struct sk_buff *)list;
  	prev = next->prev;
  	newsk->next = next;
  	newsk->prev = prev;
  	next->prev  = prev->next = newsk;
  }
  
  /**
   *	skb_queue_tail - queue a buffer at the list tail
   *	@list: list to use
   *	@newsk: buffer to queue
   *
   *	Queue a buffer at the tail of the list. This function takes the
   *	list lock and can be used safely with other locking &sk_buff functions
   *	safely.
   *
   *	A buffer cannot be placed on two lists at the same time.
   */
  static inline void skb_queue_tail(struct sk_buff_head *list,
  				  struct sk_buff *newsk)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&list->lock, flags);
  	__skb_queue_tail(list, newsk);
  	spin_unlock_irqrestore(&list->lock, flags);
  }
  
  /**
   *	__skb_dequeue - remove from the head of the queue
   *	@list: list to dequeue from
   *
   *	Remove the head of the list. This function does not take any locks
   *	so must be used with appropriate locks held only. The head item is
   *	returned or %NULL if the list is empty.
   */
  static inline struct sk_buff *__skb_dequeue(struct sk_buff_head *list)
  {
  	struct sk_buff *next, *prev, *result;
  
  	prev = (struct sk_buff *) list;
  	next = prev->next;
  	result = NULL;
  	if (next != prev) {
  		result	     = next;
  		next	     = next->next;
  		list->qlen--;
  		next->prev   = prev;
  		prev->next   = next;
  		result->next = result->prev = NULL;
  		result->list = NULL;
  	}
  	return result;
  }
  
  /**
   *	skb_dequeue - remove from the head of the queue
   *	@list: list to dequeue from
   *
   *	Remove the head of the list. The list lock is taken so the function
   *	may be used safely with other locking list functions. The head item is
   *	returned or %NULL if the list is empty.
   */
  
  static inline struct sk_buff *skb_dequeue(struct sk_buff_head *list)
  {
  	unsigned long flags;
  	struct sk_buff *result;
  
  	spin_lock_irqsave(&list->lock, flags);
  	result = __skb_dequeue(list);
  	spin_unlock_irqrestore(&list->lock, flags);
  	return result;
  }
  
  /*
   *	Insert a packet on a list.
   */
  
  static inline void __skb_insert(struct sk_buff *newsk,
  				struct sk_buff *prev, struct sk_buff *next,
  				struct sk_buff_head *list)
  {
  	newsk->next = next;
  	newsk->prev = prev;
  	next->prev  = prev->next = newsk;
  	newsk->list = list;
  	list->qlen++;
  }
  
  /**
   *	skb_insert	-	insert a buffer
   *	@old: buffer to insert before
   *	@newsk: buffer to insert
   *
   *	Place a packet before a given packet in a list. The list locks are taken
   *	and this function is atomic with respect to other list locked calls
   *	A buffer cannot be placed on two lists at the same time.
   */
  
  static inline void skb_insert(struct sk_buff *old, struct sk_buff *newsk)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&old->list->lock, flags);
  	__skb_insert(newsk, old->prev, old, old->list);
  	spin_unlock_irqrestore(&old->list->lock, flags);
  }
  
  /*
   *	Place a packet after a given packet in a list.
   */
  
  static inline void __skb_append(struct sk_buff *old, struct sk_buff *newsk)
  {
  	__skb_insert(newsk, old, old->next, old->list);
  }
  
  /**
   *	skb_append	-	append a buffer
   *	@old: buffer to insert after
   *	@newsk: buffer to insert
   *
   *	Place a packet after a given packet in a list. The list locks are taken
   *	and this function is atomic with respect to other list locked calls.
   *	A buffer cannot be placed on two lists at the same time.
   */
  
  
  static inline void skb_append(struct sk_buff *old, struct sk_buff *newsk)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&old->list->lock, flags);
  	__skb_append(old, newsk);
  	spin_unlock_irqrestore(&old->list->lock, flags);
  }
  
  /*
   * remove sk_buff from list. _Must_ be called atomically, and with
   * the list known..
   */
  static inline void __skb_unlink(struct sk_buff *skb, struct sk_buff_head *list)
  {
  	struct sk_buff *next, *prev;
  
  	list->qlen--;
  	next	   = skb->next;
  	prev	   = skb->prev;
  	skb->next  = skb->prev = NULL;
  	skb->list  = NULL;
  	next->prev = prev;
  	prev->next = next;
  }
  
  /**
   *	skb_unlink	-	remove a buffer from a list
   *	@skb: buffer to remove
   *
   *	Place a packet after a given packet in a list. The list locks are taken
   *	and this function is atomic with respect to other list locked calls
   *
   *	Works even without knowing the list it is sitting on, which can be
   *	handy at times. It also means that THE LIST MUST EXIST when you
   *	unlink. Thus a list must have its contents unlinked before it is
   *	destroyed.
   */
  static inline void skb_unlink(struct sk_buff *skb)
  {
  	struct sk_buff_head *list = skb->list;
  
  	if (list) {
  		unsigned long flags;
  
  		spin_lock_irqsave(&list->lock, flags);
  		if (skb->list == list)
  			__skb_unlink(skb, skb->list);
  		spin_unlock_irqrestore(&list->lock, flags);
  	}
  }
  
  /* XXX: more streamlined implementation */
  
  /**
   *	__skb_dequeue_tail - remove from the tail of the queue
   *	@list: list to dequeue from
   *
   *	Remove the tail of the list. This function does not take any locks
   *	so must be used with appropriate locks held only. The tail item is
   *	returned or %NULL if the list is empty.
   */
  static inline struct sk_buff *__skb_dequeue_tail(struct sk_buff_head *list)
  {
  	struct sk_buff *skb = skb_peek_tail(list);
  	if (skb)
  		__skb_unlink(skb, list);
  	return skb;
  }
  
  /**
   *	skb_dequeue - remove from the head of the queue
   *	@list: list to dequeue from
   *
   *	Remove the head of the list. The list lock is taken so the function
   *	may be used safely with other locking list functions. The tail item is
   *	returned or %NULL if the list is empty.
   */
  static inline struct sk_buff *skb_dequeue_tail(struct sk_buff_head *list)
  {
  	unsigned long flags;
  	struct sk_buff *result;
  
  	spin_lock_irqsave(&list->lock, flags);
  	result = __skb_dequeue_tail(list);
  	spin_unlock_irqrestore(&list->lock, flags);
  	return result;
  }
  
  static inline int skb_is_nonlinear(const struct sk_buff *skb)
  {
  	return skb->data_len;
  }
  
  static inline unsigned int skb_headlen(const struct sk_buff *skb)
  {
  	return skb->len - skb->data_len;
  }
  
  static inline int skb_pagelen(const struct sk_buff *skb)
  {
  	int i, len = 0;
  
  	for (i = (int)skb_shinfo(skb)->nr_frags - 1; i >= 0; i--)
  		len += skb_shinfo(skb)->frags[i].size;
  	return len + skb_headlen(skb);
  }
  
  static inline void skb_fill_page_desc(struct sk_buff *skb, int i, struct page *page, int off, int size)
  {
  	skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
  	frag->page = page;
  	frag->page_offset = off;
  	frag->size = size;
  	skb_shinfo(skb)->nr_frags = i+1;
  }
  
  #define SKB_PAGE_ASSERT(skb) 	BUG_ON(skb_shinfo(skb)->nr_frags)
  #define SKB_FRAG_ASSERT(skb) 	BUG_ON(skb_shinfo(skb)->frag_list)
  #define SKB_LINEAR_ASSERT(skb)  BUG_ON(skb_is_nonlinear(skb))
  
  /*
   *	Add data to an sk_buff
   */
  static inline unsigned char *__skb_put(struct sk_buff *skb, unsigned int len)
  {
  	unsigned char *tmp = skb->tail;
  	SKB_LINEAR_ASSERT(skb);
  	skb->tail += len;
  	skb->len  += len;
  	return tmp;
  }
  
  /**
   *	skb_put - add data to a buffer
   *	@skb: buffer to use
   *	@len: amount of data to add
   *
   *	This function extends the used data area of the buffer. If this would
   *	exceed the total buffer size the kernel will panic. A pointer to the
   *	first byte of the extra data is returned.
   */
  static inline unsigned char *skb_put(struct sk_buff *skb, unsigned int len)
  {
  	unsigned char *tmp = skb->tail;
  	SKB_LINEAR_ASSERT(skb);
  	skb->tail += len;
  	skb->len  += len;
  	if (unlikely(skb->tail>skb->end))
  		skb_over_panic(skb, len, current_text_addr());
  	return tmp;
  }
  
  static inline unsigned char *__skb_push(struct sk_buff *skb, unsigned int len)
  {
  	skb->data -= len;
  	skb->len  += len;
  	return skb->data;
  }
  
  /**
   *	skb_push - add data to the start of a buffer
   *	@skb: buffer to use
   *	@len: amount of data to add
   *
   *	This function extends the used data area of the buffer at the buffer
   *	start. If this would exceed the total buffer headroom the kernel will
   *	panic. A pointer to the first byte of the extra data is returned.
   */
  static inline unsigned char *skb_push(struct sk_buff *skb, unsigned int len)
  {
  	skb->data -= len;
  	skb->len  += len;
  	if (unlikely(skb->data<skb->head))
  		skb_under_panic(skb, len, current_text_addr());
  	return skb->data;
  }
  
  static inline char *__skb_pull(struct sk_buff *skb, unsigned int len)
  {
  	skb->len -= len;
  	BUG_ON(skb->len < skb->data_len);
  	return skb->data += len;
  }
  
  /**
   *	skb_pull - remove data from the start of a buffer
   *	@skb: buffer to use
   *	@len: amount of data to remove
   *
   *	This function removes data from the start of a buffer, returning
   *	the memory to the headroom. A pointer to the next data in the buffer
   *	is returned. Once the data has been pulled future pushes will overwrite
   *	the old data.
   */
  static inline unsigned char *skb_pull(struct sk_buff *skb, unsigned int len)
  {
  	return unlikely(len > skb->len) ? NULL : __skb_pull(skb, len);
  }
  
  extern unsigned char *__pskb_pull_tail(struct sk_buff *skb, int delta);
  
  static inline char *__pskb_pull(struct sk_buff *skb, unsigned int len)
  {
  	if (len > skb_headlen(skb) &&
  	    !__pskb_pull_tail(skb, len-skb_headlen(skb)))
  		return NULL;
  	skb->len -= len;
  	return skb->data += len;
  }
  
  static inline unsigned char *pskb_pull(struct sk_buff *skb, unsigned int len)
  {
  	return unlikely(len > skb->len) ? NULL : __pskb_pull(skb, len);
  }
  
  static inline int pskb_may_pull(struct sk_buff *skb, unsigned int len)
  {
  	if (likely(len <= skb_headlen(skb)))
  		return 1;
  	if (unlikely(len > skb->len))
  		return 0;
  	return __pskb_pull_tail(skb, len-skb_headlen(skb)) != NULL;
  }
  
  /**
   *	skb_headroom - bytes at buffer head
   *	@skb: buffer to check
   *
   *	Return the number of bytes of free space at the head of an &sk_buff.
   */
  static inline int skb_headroom(const struct sk_buff *skb)
  {
  	return skb->data - skb->head;
  }
  
  /**
   *	skb_tailroom - bytes at buffer end
   *	@skb: buffer to check
   *
   *	Return the number of bytes of free space at the tail of an sk_buff
   */
  static inline int skb_tailroom(const struct sk_buff *skb)
  {
  	return skb_is_nonlinear(skb) ? 0 : skb->end - skb->tail;
  }
  
  /**
   *	skb_reserve - adjust headroom
   *	@skb: buffer to alter
   *	@len: bytes to move
   *
   *	Increase the headroom of an empty &sk_buff by reducing the tail
   *	room. This is only allowed for an empty buffer.
   */
  static inline void skb_reserve(struct sk_buff *skb, unsigned int len)
  {
  	skb->data += len;
  	skb->tail += len;
  }
  
  extern int ___pskb_trim(struct sk_buff *skb, unsigned int len, int realloc);
  
  static inline void __skb_trim(struct sk_buff *skb, unsigned int len)
  {
  	if (!skb->data_len) {
  		skb->len  = len;
  		skb->tail = skb->data + len;
  	} else
  		___pskb_trim(skb, len, 0);
  }
  
  /**
   *	skb_trim - remove end from a buffer
   *	@skb: buffer to alter
   *	@len: new length
   *
   *	Cut the length of a buffer down by removing data from the tail. If
   *	the buffer is already under the length specified it is not modified.
   */
  static inline void skb_trim(struct sk_buff *skb, unsigned int len)
  {
  	if (skb->len > len)
  		__skb_trim(skb, len);
  }
  
  
  static inline int __pskb_trim(struct sk_buff *skb, unsigned int len)
  {
  	if (!skb->data_len) {
  		skb->len  = len;
  		skb->tail = skb->data+len;
  		return 0;
  	}
  	return ___pskb_trim(skb, len, 1);
  }
  
  static inline int pskb_trim(struct sk_buff *skb, unsigned int len)
  {
  	return (len < skb->len) ? __pskb_trim(skb, len) : 0;
  }
  
  /**
   *	skb_orphan - orphan a buffer
   *	@skb: buffer to orphan
   *
   *	If a buffer currently has an owner then we call the owner's
   *	destructor function and make the @skb unowned. The buffer continues
   *	to exist but is no longer charged to its former owner.
   */
  static inline void skb_orphan(struct sk_buff *skb)
  {
  	if (skb->destructor)
  		skb->destructor(skb);
  	skb->destructor = NULL;
  	skb->sk		= NULL;
  }
  
  /**
   *	skb_queue_purge - empty a list
   *	@list: list to empty
   *
   *	Delete all buffers on an &sk_buff list. Each buffer is removed from
   *	the list and one reference dropped. This function takes the list
   *	lock and is atomic with respect to other list locking functions.
   */
  static inline void skb_queue_purge(struct sk_buff_head *list)
  {
  	struct sk_buff *skb;
  	while ((skb = skb_dequeue(list)) != NULL)
  		kfree_skb(skb);
  }
  
  /**
   *	__skb_queue_purge - empty a list
   *	@list: list to empty
   *
   *	Delete all buffers on an &sk_buff list. Each buffer is removed from
   *	the list and one reference dropped. This function does not take the
   *	list lock and the caller must hold the relevant locks to use it.
   */
  static inline void __skb_queue_purge(struct sk_buff_head *list)
  {
  	struct sk_buff *skb;
  	while ((skb = __skb_dequeue(list)) != NULL)
  		kfree_skb(skb);
  }
  
  /**
   *	__dev_alloc_skb - allocate an skbuff for sending
   *	@length: length to allocate
   *	@gfp_mask: get_free_pages mask, passed to alloc_skb
   *
   *	Allocate a new &sk_buff and assign it a usage count of one. The
   *	buffer has unspecified headroom built in. Users should allocate
   *	the headroom they think they need without accounting for the
   *	built in space. The built in space is used for optimisations.
   *
   *	%NULL is returned in there is no free memory.
   */
  static inline struct sk_buff *__dev_alloc_skb(unsigned int length,
  					      int gfp_mask)
  {
  	struct sk_buff *skb = alloc_skb(length + 16, gfp_mask);
  	if (likely(skb))
  		skb_reserve(skb, 16);
  	return skb;
  }
  
  /**
   *	dev_alloc_skb - allocate an skbuff for sending
   *	@length: length to allocate
   *
   *	Allocate a new &sk_buff and assign it a usage count of one. The
   *	buffer has unspecified headroom built in. Users should allocate
   *	the headroom they think they need without accounting for the
   *	built in space. The built in space is used for optimisations.
   *
   *	%NULL is returned in there is no free memory. Although this function
   *	allocates memory it can be called from an interrupt.
   */
  static inline struct sk_buff *dev_alloc_skb(unsigned int length)
  {
  	return __dev_alloc_skb(length, GFP_ATOMIC);
  }
  
  /**
   *	skb_cow - copy header of skb when it is required
   *	@skb: buffer to cow
   *	@headroom: needed headroom
   *
   *	If the skb passed lacks sufficient headroom or its data part
   *	is shared, data is reallocated. If reallocation fails, an error
   *	is returned and original skb is not changed.
   *
   *	The result is skb with writable area skb->head...skb->tail
   *	and at least @headroom of space at head.
   */
  static inline int skb_cow(struct sk_buff *skb, unsigned int headroom)
  {
  	int delta = (headroom > 16 ? headroom : 16) - skb_headroom(skb);
  
  	if (delta < 0)
  		delta = 0;
  
  	if (delta || skb_cloned(skb))
  		return pskb_expand_head(skb, (delta + 15) & ~15, 0, GFP_ATOMIC);
  	return 0;
  }
  
  /**
   *	skb_padto	- pad an skbuff up to a minimal size
   *	@skb: buffer to pad
   *	@len: minimal length
   *
   *	Pads up a buffer to ensure the trailing bytes exist and are
   *	blanked. If the buffer already contains sufficient data it
   *	is untouched. Returns the buffer, which may be a replacement
   *	for the original, or NULL for out of memory - in which case
   *	the original buffer is still freed.
   */
   
  static inline struct sk_buff *skb_padto(struct sk_buff *skb, unsigned int len)
  {
  	unsigned int size = skb->len;
  	if (likely(size >= len))
  		return skb;
  	return skb_pad(skb, len-size);
  }
  
  /**
   *	skb_linearize - convert paged skb to linear one
   *	@skb: buffer to linarize
   *	@gfp: allocation mode
   *
   *	If there is no free memory -ENOMEM is returned, otherwise zero
   *	is returned and the old skb data released.
   */
  extern int __skb_linearize(struct sk_buff *skb, int gfp);
  static inline int __deprecated skb_linearize(struct sk_buff *skb, int gfp)
  {
  	return __skb_linearize(skb, gfp);
  }
  
  static inline void *kmap_skb_frag(const skb_frag_t *frag)
  {
  #ifdef CONFIG_HIGHMEM
  	BUG_ON(in_irq());
  
  	local_bh_disable();
  #endif
  	return kmap_atomic(frag->page, KM_SKB_DATA_SOFTIRQ);
  }
  
  static inline void kunmap_skb_frag(void *vaddr)
  {
  	kunmap_atomic(vaddr, KM_SKB_DATA_SOFTIRQ);
  #ifdef CONFIG_HIGHMEM
  	local_bh_enable();
  #endif
  }
  
  #define skb_queue_walk(queue, skb) \
  		for (skb = (queue)->next, prefetch(skb->next);	\
  		     (skb != (struct sk_buff *)(queue));	\
  		     skb = skb->next, prefetch(skb->next))
  
  
  extern struct sk_buff *skb_recv_datagram(struct sock *sk, unsigned flags,
  					 int noblock, int *err);
  extern unsigned int    datagram_poll(struct file *file, struct socket *sock,
  				     struct poll_table_struct *wait);
  extern int	       skb_copy_datagram(const struct sk_buff *from,
  					 int offset, char *to, int size);
  extern int	       skb_copy_datagram_iovec(const struct sk_buff *from,
  					       int offset, struct iovec *to,
  					       int size);
  extern int	       skb_copy_and_csum_datagram(const struct sk_buff *skb,
  						  int offset, u8 *to, int len,
  						  unsigned int *csump);
  extern int	       skb_copy_and_csum_datagram_iovec(const
  							struct sk_buff *skb,
  							int hlen,
  							struct iovec *iov);
  extern void	       skb_free_datagram(struct sock *sk, struct sk_buff *skb);
  extern unsigned int    skb_checksum(const struct sk_buff *skb, int offset,
  				    int len, unsigned int csum);
  extern int	       skb_copy_bits(const struct sk_buff *skb, int offset,
  				     void *to, int len);
  extern unsigned int    skb_copy_and_csum_bits(const struct sk_buff *skb,
  					      int offset, u8 *to, int len,
  					      unsigned int csum);
  extern void	       skb_copy_and_csum_dev(const struct sk_buff *skb, u8 *to);
  
  extern void skb_init(void);
  extern void skb_add_mtu(int mtu);
  
  #ifdef CONFIG_NETFILTER
  static inline void nf_conntrack_put(struct nf_ct_info *nfct)
  {
  	if (nfct && atomic_dec_and_test(&nfct->master->use))
  		nfct->master->destroy(nfct->master);
  }
  static inline void nf_conntrack_get(struct nf_ct_info *nfct)
  {
  	if (nfct)
  		atomic_inc(&nfct->master->use);
  }
  
  #ifdef CONFIG_BRIDGE_NETFILTER
  static inline void nf_bridge_put(struct nf_bridge_info *nf_bridge)
  {
  	if (nf_bridge && atomic_dec_and_test(&nf_bridge->use))
  		kfree(nf_bridge);
  }
  static inline void nf_bridge_get(struct nf_bridge_info *nf_bridge)
  {
  	if (nf_bridge)
  		atomic_inc(&nf_bridge->use);
  }
  #endif
  
  #endif
  
  #endif	/* __KERNEL__ */
  #endif	/* _LINUX_SKBUFF_H */
  