skbuff.h

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/*
 *      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/sched.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>

#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;
};
#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;

#define MAX_SKB_FRAGS 6

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;
        struct sk_buff  *frag_list;
        skb_frag_t      frags[MAX_SKB_FRAGS];
};

struct sk_buff {
        /* These two members must be first. */
        struct sk_buff  * next;                 /* Next buffer in list                          */
        struct sk_buff  * prev;                 /* Previous buffer in list                      */

        struct sk_buff_head * list;             /* List we are on                               */
        struct sock     *sk;                    /* Socket we are owned by                       */
        struct timeval  stamp;                  /* Time we arrived                              */
        struct net_device       *dev;           /* Device we arrived on/are leaving by          */
        struct net_device       *real_dev;      /* For support of point to point protocols 
                                                   (e.g. 802.3ad) over bonding, we must save the
                                                   physical device that got the packet before
                                                   replacing skb->dev with the virtual device.  */

        /* Transport layer header */
        union
        {
                struct tcphdr   *th;
                struct udphdr   *uh;
                struct icmphdr  *icmph;
                struct igmphdr  *igmph;
                struct iphdr    *ipiph;
                struct spxhdr   *spxh;
                unsigned char   *raw;
        } h;

        /* Network layer header */
        union
        {
                struct iphdr    *iph;
                struct ipv6hdr  *ipv6h;
                struct arphdr   *arph;
                struct ipxhdr   *ipxh;
                unsigned char   *raw;
        } nh;
  
        /* Link layer header */
        union 
        {       
                struct ethhdr   *ethernet;
                unsigned char   *raw;
        } mac;

        struct  dst_entry *dst;

        /* 
         * 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;                    /* Length of actual data                        */
        unsigned int    data_len;
        unsigned int    csum;                   /* Checksum                                     */
        unsigned char   __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                 */
        __u32           priority;               /* Packet queueing priority                     */
        atomic_t        users;                  /* User count - see datagram.c,tcp.c            */
        unsigned short  protocol;               /* Packet protocol from driver.                 */
        unsigned short  security;               /* Security level of packet                     */
        unsigned int    truesize;               /* Buffer size                                  */

        unsigned char   *head;                  /* Head of buffer                               */
        unsigned char   *data;                  /* Data head pointer                            */
        unsigned char   *tail;                  /* Tail pointer                                 */
        unsigned char   *end;                   /* End pointer                                  */

        void            (*destructor)(struct sk_buff *);        /* Destruct function            */
#ifdef CONFIG_NETFILTER
        /* Can be used for communication between hooks. */
        unsigned long   nfmark;
        /* Cache info */
        __u32           nfcache;
        /* Associated connection, if any */
        struct nf_ct_info *nfct;
#ifdef CONFIG_NETFILTER_DEBUG
        unsigned int nf_debug;
#endif
#endif /*CONFIG_NETFILTER*/

#if defined(CONFIG_HIPPI)
        union{
                __u32   ifield;
        } private;
#endif

#ifdef CONFIG_NET_SCHED
       __u32           tc_index;               /* traffic control index */
#endif
};

#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(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(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(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)
{
        if (skb_shared(skb)) {
                struct sk_buff *nskb;
                nskb = skb_clone(skb, pri);
                kfree_skb(skb);
                return 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)
{
        struct sk_buff *nskb;
        if(!skb_cloned(skb))
                return skb;
        nskb=skb_copy(skb, pri);
        kfree_skb(skb);         /* Free our shared copy */
        return nskb;
}

/*
 *      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(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 = (struct sk_buff *)list;
        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 = newsk;
        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 = newsk;
        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 = NULL;
                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 = newsk;
        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 = NULL;
        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;
}

#define SKB_PAGE_ASSERT(skb) do { if (skb_shinfo(skb)->nr_frags) out_of_line_bug(); } while (0)
#define SKB_FRAG_ASSERT(skb) do { if (skb_shinfo(skb)->frag_list) out_of_line_bug(); } while (0)
#define SKB_LINEAR_ASSERT(skb) do { if (skb_is_nonlinear(skb)) out_of_line_bug(); } while (0)

/*
 *      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(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(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;
        if (skb->len < skb->data_len)
                out_of_line_bug();
        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)
{       
        if (len > skb->len)
                return NULL;
        return __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)) == NULL)
                return NULL;
        skb->len -= len;
        return  skb->data += len;
}

static inline unsigned char * pskb_pull(struct sk_buff *skb, unsigned int len)
{       
        if (len > skb->len)
                return NULL;
        return __pskb_pull(skb,len);
}

static inline int pskb_may_pull(struct sk_buff *skb, unsigned int len)
{
        if (len <= skb_headlen(skb))
                return 1;
        if (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;
        } else {
                return ___pskb_trim(skb, len, 1);
        }
}

static inline int pskb_trim(struct sk_buff *skb, unsigned int len)
{
        if (len < skb->len)
                return __pskb_trim(skb, len);
        return 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_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_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;

        skb = alloc_skb(length+16, gfp_mask);
        if (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.  */
int skb_linearize(struct sk_buff *skb, int gfp);

static inline void *kmap_skb_frag(const skb_frag_t *frag)
{
#ifdef CONFIG_HIGHMEM
        if (in_irq())
                out_of_line_bug();

        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;                       \
                     (skb != (struct sk_buff *)(queue));        \
                     skb=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);
}
#endif

#endif  /* __KERNEL__ */
#endif  /* _LINUX_SKBUFF_H */

---