net: skb->rtable accessor

[safe/jmp/linux-2.6] / include / linux / skbuff.h

/*
 *      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/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/net.h>
#include <linux/textsearch.h>
#include <net/checksum.h>
#include <linux/rcupdate.h>
#include <linux/dmaengine.h>
#include <linux/hrtimer.h>

/* Don't change this without changing skb_csum_unnecessary! */
#define CHECKSUM_NONE 0
#define CHECKSUM_UNNECESSARY 1
#define CHECKSUM_COMPLETE 2
#define CHECKSUM_PARTIAL 3

#define SKB_DATA_ALIGN(X)       (((X) + (SMP_CACHE_BYTES - 1)) & \
                                 ~(SMP_CACHE_BYTES - 1))
#define SKB_WITH_OVERHEAD(X)    \
        ((X) - SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
#define SKB_MAX_ORDER(X, ORDER) \
        SKB_WITH_OVERHEAD((PAGE_SIZE << (ORDER)) - (X))
#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)
 *
 *      COMPLETE: 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 COMPLETE,
 *          not UNNECESSARY.
 *
 *      PARTIAL: identical to the case for output below.  This may occur
 *          on a packet received directly from another Linux OS, e.g.,
 *          a virtualised Linux kernel on the same host.  The packet can
 *          be treated in the same way as UNNECESSARY except that on
 *          output (i.e., forwarding) the checksum must be filled in
 *          by the OS or the hardware.
 *
 * B. Checksumming on output.
 *
 *      NONE: skb is checksummed by protocol or csum is not required.
 *
 *      PARTIAL: device is required to csum packet as seen by hard_start_xmit
 *      from skb->csum_start to the end and to record the checksum
 *      at skb->csum_start + skb->csum_offset.
 *
 *      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)
 *      NETIF_F_IPV6_CSUM about as dumb as the last one but does IPv6 instead.
 *
 *      Any questions? No questions, good.              --ANK
 */

struct net_device;
struct scatterlist;
struct pipe_inode_info;

#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
struct nf_conntrack {
        atomic_t use;
};
#endif

#ifdef CONFIG_BRIDGE_NETFILTER
struct nf_bridge_info {
        atomic_t use;
        struct net_device *physindev;
        struct net_device *physoutdev;
        unsigned int mask;
        unsigned long data[32 / sizeof(unsigned long)];
};
#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;
        __u32 page_offset;
        __u32 size;
};

#define HAVE_HW_TIME_STAMP

/**
 * struct skb_shared_hwtstamps - hardware time stamps
 * @hwtstamp:   hardware time stamp transformed into duration
 *              since arbitrary point in time
 * @syststamp:  hwtstamp transformed to system time base
 *
 * Software time stamps generated by ktime_get_real() are stored in
 * skb->tstamp. The relation between the different kinds of time
 * stamps is as follows:
 *
 * syststamp and tstamp can be compared against each other in
 * arbitrary combinations.  The accuracy of a
 * syststamp/tstamp/"syststamp from other device" comparison is
 * limited by the accuracy of the transformation into system time
 * base. This depends on the device driver and its underlying
 * hardware.
 *
 * hwtstamps can only be compared against other hwtstamps from
 * the same device.
 *
 * This structure is attached to packets as part of the
 * &skb_shared_info. Use skb_hwtstamps() to get a pointer.
 */
struct skb_shared_hwtstamps {
        ktime_t hwtstamp;
        ktime_t syststamp;
};

/**
 * struct skb_shared_tx - instructions for time stamping of outgoing packets
 * @hardware:           generate hardware time stamp
 * @software:           generate software time stamp
 * @in_progress:        device driver is going to provide
 *                      hardware time stamp
 * @flags:              all shared_tx flags
 *
 * These flags are attached to packets as part of the
 * &skb_shared_info. Use skb_tx() to get a pointer.
 */
union skb_shared_tx {
        struct {
                __u8    hardware:1,
                        software:1,
                        in_progress:1;
        };
        __u8 flags;
};

/* 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 short  nr_frags;
        unsigned short  gso_size;
        /* Warning: this field is not always filled in (UFO)! */
        unsigned short  gso_segs;
        unsigned short  gso_type;
        __be32          ip6_frag_id;
        union skb_shared_tx tx_flags;
#ifdef CONFIG_HAS_DMA
        unsigned int    num_dma_maps;
#endif
        struct sk_buff  *frag_list;
        struct skb_shared_hwtstamps hwtstamps;
        skb_frag_t      frags[MAX_SKB_FRAGS];
#ifdef CONFIG_HAS_DMA
        dma_addr_t      dma_maps[MAX_SKB_FRAGS + 1];
#endif
        /* Intermediate layers must ensure that destructor_arg
         * remains valid until skb destructor */
        void *          destructor_arg;
};

/* We divide dataref into two halves.  The higher 16 bits hold references
 * to the payload part of skb->data.  The lower 16 bits hold references to
 * the entire skb->data.  A clone of a headerless skb holds the length of
 * the header in skb->hdr_len.
 *
 * All users must obey the rule that the skb->data reference count must be
 * greater than or equal to the payload reference count.
 *
 * Holding a reference to the payload part means that the user does not
 * care about modifications to the header part of skb->data.
 */
#define SKB_DATAREF_SHIFT 16
#define SKB_DATAREF_MASK ((1 << SKB_DATAREF_SHIFT) - 1)


enum {
        SKB_FCLONE_UNAVAILABLE,
        SKB_FCLONE_ORIG,
        SKB_FCLONE_CLONE,
};

enum {
        SKB_GSO_TCPV4 = 1 << 0,
        SKB_GSO_UDP = 1 << 1,

        /* This indicates the skb is from an untrusted source. */
        SKB_GSO_DODGY = 1 << 2,

        /* This indicates the tcp segment has CWR set. */
        SKB_GSO_TCP_ECN = 1 << 3,

        SKB_GSO_TCPV6 = 1 << 4,

        SKB_GSO_FCOE = 1 << 5,
};

#if BITS_PER_LONG > 32
#define NET_SKBUFF_DATA_USES_OFFSET 1
#endif

#ifdef NET_SKBUFF_DATA_USES_OFFSET
typedef unsigned int sk_buff_data_t;
#else
typedef unsigned char *sk_buff_data_t;
#endif

/** 
 *      struct sk_buff - socket buffer
 *      @next: Next buffer in list
 *      @prev: Previous buffer in list
 *      @sk: Socket we are owned by
 *      @tstamp: Time we arrived
 *      @dev: Device we arrived on/are leaving by
 *      @transport_header: Transport layer header
 *      @network_header: Network layer header
 *      @mac_header: Link layer header
 *      @dst: destination entry
 *      @sp: the security path, used for xfrm
 *      @cb: Control buffer. Free for use by every layer. Put private vars here
 *      @len: Length of actual data
 *      @data_len: Data length
 *      @mac_len: Length of link layer header
 *      @hdr_len: writable header length of cloned skb
 *      @csum: Checksum (must include start/offset pair)
 *      @csum_start: Offset from skb->head where checksumming should start
 *      @csum_offset: Offset from csum_start where checksum should be stored
 *      @local_df: allow local fragmentation
 *      @cloned: Head may be cloned (check refcnt to be sure)
 *      @nohdr: Payload reference only, must not modify header
 *      @pkt_type: Packet class
 *      @fclone: skbuff clone status
 *      @ip_summed: Driver fed us an IP checksum
 *      @priority: Packet queueing priority
 *      @users: User count - see {datagram,tcp}.c
 *      @protocol: Packet protocol from driver
 *      @truesize: Buffer size 
 *      @head: Head of buffer
 *      @data: Data head pointer
 *      @tail: Tail pointer
 *      @end: End pointer
 *      @destructor: Destruct function
 *      @mark: Generic packet mark
 *      @nfct: Associated connection, if any
 *      @ipvs_property: skbuff is owned by ipvs
 *      @peeked: this packet has been seen already, so stats have been
 *              done for it, don't do them again
 *      @nf_trace: netfilter packet trace flag
 *      @nfctinfo: Relationship of this skb to the connection
 *      @nfct_reasm: netfilter conntrack re-assembly pointer
 *      @nf_bridge: Saved data about a bridged frame - see br_netfilter.c
 *      @iif: ifindex of device we arrived on
 *      @queue_mapping: Queue mapping for multiqueue devices
 *      @tc_index: Traffic control index
 *      @tc_verd: traffic control verdict
 *      @ndisc_nodetype: router type (from link layer)
 *      @do_not_encrypt: set to prevent encryption of this frame
 *      @requeue: set to indicate that the wireless core should attempt
 *              a software retry on this frame if we failed to
 *              receive an ACK for it
 *      @dma_cookie: a cookie to one of several possible DMA operations
 *              done by skb DMA functions
 *      @secmark: security marking
 *      @vlan_tci: vlan tag control information
 */

struct sk_buff {
        /* These two members must be first. */
        struct sk_buff          *next;
        struct sk_buff          *prev;

        struct sock             *sk;
        ktime_t                 tstamp;
        struct net_device       *dev;

        union {
                struct  dst_entry       *dst;
                unsigned long           _skb_dst;
        };
#ifdef CONFIG_XFRM
        struct  sec_path        *sp;
#endif
        /*
         * 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;
        __u16                   mac_len,
                                hdr_len;
        union {
                __wsum          csum;
                struct {
                        __u16   csum_start;
                        __u16   csum_offset;
                };
        };
        __u32                   priority;
        __u8                    local_df:1,
                                cloned:1,
                                ip_summed:2,
                                nohdr:1,
                                nfctinfo:3;
        __u8                    pkt_type:3,
                                fclone:2,
                                ipvs_property:1,
                                peeked:1,
                                nf_trace:1;
        __be16                  protocol;

        void                    (*destructor)(struct sk_buff *skb);
#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
        struct nf_conntrack     *nfct;
        struct sk_buff          *nfct_reasm;
#endif
#ifdef CONFIG_BRIDGE_NETFILTER
        struct nf_bridge_info   *nf_bridge;
#endif

        int                     iif;
        __u16                   queue_mapping;
#ifdef CONFIG_NET_SCHED
        __u16                   tc_index;       /* traffic control index */
#ifdef CONFIG_NET_CLS_ACT
        __u16                   tc_verd;        /* traffic control verdict */
#endif
#endif
#ifdef CONFIG_IPV6_NDISC_NODETYPE
        __u8                    ndisc_nodetype:2;
#endif
#if defined(CONFIG_MAC80211) || defined(CONFIG_MAC80211_MODULE)
        __u8                    do_not_encrypt:1;
        __u8                    requeue:1;
#endif
        /* 0/13/14 bit hole */

#ifdef CONFIG_NET_DMA
        dma_cookie_t            dma_cookie;
#endif
#ifdef CONFIG_NETWORK_SECMARK
        __u32                   secmark;
#endif

        __u32                   mark;

        __u16                   vlan_tci;

        sk_buff_data_t          transport_header;
        sk_buff_data_t          network_header;
        sk_buff_data_t          mac_header;
        /* These elements must be at the end, see alloc_skb() for details.  */
        sk_buff_data_t          tail;
        sk_buff_data_t          end;
        unsigned char           *head,
                                *data;
        unsigned int            truesize;
        atomic_t                users;
};

#ifdef __KERNEL__
/*
 *      Handling routines are only of interest to the kernel
 */
#include <linux/slab.h>

#include <asm/system.h>

#ifdef CONFIG_HAS_DMA
#include <linux/dma-mapping.h>
extern int skb_dma_map(struct device *dev, struct sk_buff *skb,
                       enum dma_data_direction dir);
extern void skb_dma_unmap(struct device *dev, struct sk_buff *skb,
                          enum dma_data_direction dir);
#endif

static inline struct rtable *skb_rtable(const struct sk_buff *skb)
{
        return (struct rtable *)skb->_skb_dst;
}

extern void kfree_skb(struct sk_buff *skb);
extern void consume_skb(struct sk_buff *skb);
extern void            __kfree_skb(struct sk_buff *skb);
extern struct sk_buff *__alloc_skb(unsigned int size,
                                   gfp_t priority, int fclone, int node);
static inline struct sk_buff *alloc_skb(unsigned int size,
                                        gfp_t priority)
{
        return __alloc_skb(size, priority, 0, -1);
}

static inline struct sk_buff *alloc_skb_fclone(unsigned int size,
                                               gfp_t priority)
{
        return __alloc_skb(size, priority, 1, -1);
}

extern int skb_recycle_check(struct sk_buff *skb, int skb_size);

extern struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src);
extern struct sk_buff *skb_clone(struct sk_buff *skb,
                                 gfp_t priority);
extern struct sk_buff *skb_copy(const struct sk_buff *skb,
                                gfp_t priority);
extern struct sk_buff *pskb_copy(struct sk_buff *skb,
                                 gfp_t gfp_mask);
extern int             pskb_expand_head(struct sk_buff *skb,
                                        int nhead, int ntail,
                                        gfp_t 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,
                                       gfp_t priority);
extern int             skb_to_sgvec(struct sk_buff *skb,
                                    struct scatterlist *sg, int offset,
                                    int len);
extern int             skb_cow_data(struct sk_buff *skb, int tailbits,
                                    struct sk_buff **trailer);
extern int             skb_pad(struct sk_buff *skb, int pad);
#define dev_kfree_skb(a)        consume_skb(a)
#define dev_consume_skb(a)      kfree_skb_clean(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);

extern int skb_append_datato_frags(struct sock *sk, struct sk_buff *skb,
                        int getfrag(void *from, char *to, int offset,
                        int len,int odd, struct sk_buff *skb),
                        void *from, int length);

struct skb_seq_state
{
        __u32           lower_offset;
        __u32           upper_offset;
        __u32           frag_idx;
        __u32           stepped_offset;
        struct sk_buff  *root_skb;
        struct sk_buff  *cur_skb;
        __u8            *frag_data;
};

extern void           skb_prepare_seq_read(struct sk_buff *skb,
                                           unsigned int from, unsigned int to,
                                           struct skb_seq_state *st);
extern unsigned int   skb_seq_read(unsigned int consumed, const u8 **data,
                                   struct skb_seq_state *st);
extern void           skb_abort_seq_read(struct skb_seq_state *st);

extern unsigned int   skb_find_text(struct sk_buff *skb, unsigned int from,
                                    unsigned int to, struct ts_config *config,
                                    struct ts_state *state);

#ifdef NET_SKBUFF_DATA_USES_OFFSET
static inline unsigned char *skb_end_pointer(const struct sk_buff *skb)
{
        return skb->head + skb->end;
}
#else
static inline unsigned char *skb_end_pointer(const struct sk_buff *skb)
{
        return skb->end;
}
#endif

/* Internal */
#define skb_shinfo(SKB) ((struct skb_shared_info *)(skb_end_pointer(SKB)))

static inline struct skb_shared_hwtstamps *skb_hwtstamps(struct sk_buff *skb)
{
        return &skb_shinfo(skb)->hwtstamps;
}

static inline union skb_shared_tx *skb_tx(struct sk_buff *skb)
{
        return &skb_shinfo(skb)->tx_flags;
}

/**
 *      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_queue_is_last - check if skb is the last entry in the queue
 *      @list: queue head
 *      @skb: buffer
 *
 *      Returns true if @skb is the last buffer on the list.
 */
static inline bool skb_queue_is_last(const struct sk_buff_head *list,
                                     const struct sk_buff *skb)
{
        return (skb->next == (struct sk_buff *) list);
}

/**
 *      skb_queue_is_first - check if skb is the first entry in the queue
 *      @list: queue head
 *      @skb: buffer
 *
 *      Returns true if @skb is the first buffer on the list.
 */
static inline bool skb_queue_is_first(const struct sk_buff_head *list,
                                      const struct sk_buff *skb)
{
        return (skb->prev == (struct sk_buff *) list);
}

/**
 *      skb_queue_next - return the next packet in the queue
 *      @list: queue head
 *      @skb: current buffer
 *
 *      Return the next packet in @list after @skb.  It is only valid to
 *      call this if skb_queue_is_last() evaluates to false.
 */
static inline struct sk_buff *skb_queue_next(const struct sk_buff_head *list,
                                             const struct sk_buff *skb)
{
        /* This BUG_ON may seem severe, but if we just return then we
         * are going to dereference garbage.
         */
        BUG_ON(skb_queue_is_last(list, skb));
        return skb->next;
}

/**
 *      skb_queue_prev - return the prev packet in the queue
 *      @list: queue head
 *      @skb: current buffer
 *
 *      Return the prev packet in @list before @skb.  It is only valid to
 *      call this if skb_queue_is_first() evaluates to false.
 */
static inline struct sk_buff *skb_queue_prev(const struct sk_buff_head *list,
                                             const struct sk_buff *skb)
{
        /* This BUG_ON may seem severe, but if we just return then we
         * are going to dereference garbage.
         */
        BUG_ON(skb_queue_is_first(list, skb));
        return skb->prev;
}

/**
 *      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.
 */

/**
 *      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) & SKB_DATAREF_MASK) != 1;
}

/**
 *      skb_header_cloned - is the header a clone
 *      @skb: buffer to check
 *
 *      Returns true if modifying the header part of the buffer requires
 *      the data to be copied.
 */
static inline int skb_header_cloned(const struct sk_buff *skb)
{
        int dataref;

        if (!skb->cloned)
                return 0;

        dataref = atomic_read(&skb_shinfo(skb)->dataref);
        dataref = (dataref & SKB_DATAREF_MASK) - (dataref >> SKB_DATAREF_SHIFT);
        return dataref != 1;
}

/**
 *      skb_header_release - release reference to header
 *      @skb: buffer to operate on
 *
 *      Drop a reference to the header part of the buffer.  This is done
 *      by acquiring a payload reference.  You must not read from the header
 *      part of skb->data after this.
 */
static inline void skb_header_release(struct sk_buff *skb)
{
        BUG_ON(skb->nohdr);
        skb->nohdr = 1;
        atomic_add(1 << SKB_DATAREF_SHIFT, &skb_shinfo(skb)->dataref);
}

/**
 *      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,
                                              gfp_t 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,
                                          gfp_t 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;
}

/**
 *      __skb_queue_head_init - initialize non-spinlock portions of sk_buff_head
 *      @list: queue to initialize
 *
 *      This initializes only the list and queue length aspects of
 *      an sk_buff_head object.  This allows to initialize the list
 *      aspects of an sk_buff_head without reinitializing things like
 *      the spinlock.  It can also be used for on-stack sk_buff_head
 *      objects where the spinlock is known to not be used.
 */
static inline void __skb_queue_head_init(struct sk_buff_head *list)
{
        list->prev = list->next = (struct sk_buff *)list;
        list->qlen = 0;
}

/*
 * This function creates a split out lock class for each invocation;
 * this is needed for now since a whole lot of users of the skb-queue
 * infrastructure in drivers have different locking usage (in hardirq)
 * than the networking core (in softirq only). In the long run either the
 * network layer or drivers should need annotation to consolidate the
 * main types of usage into 3 classes.
 */
static inline void skb_queue_head_init(struct sk_buff_head *list)
{
        spin_lock_init(&list->lock);
        __skb_queue_head_init(list);
}

static inline void skb_queue_head_init_class(struct sk_buff_head *list,
                struct lock_class_key *class)
{
        skb_queue_head_init(list);
        lockdep_set_class(&list->lock, class);
}

/*
 *      Insert an sk_buff on a list.
 *
 *      The "__skb_xxxx()" functions are the non-atomic ones that
 *      can only be called with interrupts disabled.
 */
extern void        skb_insert(struct sk_buff *old, struct sk_buff *newsk, struct sk_buff_head *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;
        list->qlen++;
}

static inline void __skb_queue_splice(const struct sk_buff_head *list,
                                      struct sk_buff *prev,
                                      struct sk_buff *next)
{
        struct sk_buff *first = list->next;
        struct sk_buff *last = list->prev;

        first->prev = prev;
        prev->next = first;

        last->next = next;
        next->prev = last;
}

/**
 *      skb_queue_splice - join two skb lists, this is designed for stacks
 *      @list: the new list to add
 *      @head: the place to add it in the first list
 */
static inline void skb_queue_splice(const struct sk_buff_head *list,
                                    struct sk_buff_head *head)
{
        if (!skb_queue_empty(list)) {
                __skb_queue_splice(list, (struct sk_buff *) head, head->next);
                head->qlen += list->qlen;
        }
}

/**
 *      skb_queue_splice - join two skb lists and reinitialise the emptied list
 *      @list: the new list to add
 *      @head: the place to add it in the first list
 *
 *      The list at @list is reinitialised
 */
static inline void skb_queue_splice_init(struct sk_buff_head *list,
                                         struct sk_buff_head *head)
{
        if (!skb_queue_empty(list)) {
                __skb_queue_splice(list, (struct sk_buff *) head, head->next);
                head->qlen += list->qlen;
                __skb_queue_head_init(list);
        }
}

/**
 *      skb_queue_splice_tail - join two skb lists, each list being a queue
 *      @list: the new list to add
 *      @head: the place to add it in the first list
 */
static inline void skb_queue_splice_tail(const struct sk_buff_head *list,
                                         struct sk_buff_head *head)
{
        if (!skb_queue_empty(list)) {
                __skb_queue_splice(list, head->prev, (struct sk_buff *) head);
                head->qlen += list->qlen;
        }
}

/**
 *      skb_queue_splice_tail - join two skb lists and reinitialise the emptied list
 *      @list: the new list to add
 *      @head: the place to add it in the first list
 *
 *      Each of the lists is a queue.
 *      The list at @list is reinitialised
 */
static inline void skb_queue_splice_tail_init(struct sk_buff_head *list,
                                              struct sk_buff_head *head)
{
        if (!skb_queue_empty(list)) {
                __skb_queue_splice(list, head->prev, (struct sk_buff *) head);
                head->qlen += list->qlen;
                __skb_queue_head_init(list);
        }
}

/**
 *      __skb_queue_after - queue a buffer at the list head
 *      @list: list to use
 *      @prev: place after this buffer
 *      @newsk: buffer to queue
 *
 *      Queue a buffer int the middle 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_after(struct sk_buff_head *list,
                                     struct sk_buff *prev,
                                     struct sk_buff *newsk)
{
        __skb_insert(newsk, prev, prev->next, list);
}

extern void skb_append(struct sk_buff *old, struct sk_buff *newsk,
                       struct sk_buff_head *list);

static inline void __skb_queue_before(struct sk_buff_head *list,
                                      struct sk_buff *next,
                                      struct sk_buff *newsk)
{
        __skb_insert(newsk, next->prev, next, list);
}

/**
 *      __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.
 */
extern void skb_queue_head(struct sk_buff_head *list, struct sk_buff *newsk);
static inline void __skb_queue_head(struct sk_buff_head *list,
                                    struct sk_buff *newsk)
{
        __skb_queue_after(list, (struct sk_buff *)list, newsk);
}

/**
 *      __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.
 */
extern void skb_queue_tail(struct sk_buff_head *list, struct sk_buff *newsk);
static inline void __skb_queue_tail(struct sk_buff_head *list,
                                   struct sk_buff *newsk)
{
        __skb_queue_before(list, (struct sk_buff *)list, newsk);
}

/*
 * remove sk_buff from list. _Must_ be called atomically, and with
 * the list known..
 */
extern void        skb_unlink(struct sk_buff *skb, struct sk_buff_head *list);
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;
        next->prev = prev;
        prev->next = next;
}

/**
 *      __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.
 */
extern struct sk_buff *skb_dequeue(struct sk_buff_head *list);
static inline struct sk_buff *__skb_dequeue(struct sk_buff_head *list)
{
        struct sk_buff *skb = skb_peek(list);
        if (skb)
                __skb_unlink(skb, list);
        return skb;
}

/**
 *      __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.
 */
extern struct sk_buff *skb_dequeue_tail(struct sk_buff_head *list);
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;
}


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;
}

extern void skb_add_rx_frag(struct sk_buff *skb, int i, struct page *page,
                            int off, int size);

#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))

#ifdef NET_SKBUFF_DATA_USES_OFFSET
static inline unsigned char *skb_tail_pointer(const struct sk_buff *skb)
{
        return skb->head + skb->tail;
}

static inline void skb_reset_tail_pointer(struct sk_buff *skb)
{
        skb->tail = skb->data - skb->head;
}

static inline void skb_set_tail_pointer(struct sk_buff *skb, const int offset)
{
        skb_reset_tail_pointer(skb);
        skb->tail += offset;
}
#else /* NET_SKBUFF_DATA_USES_OFFSET */
static inline unsigned char *skb_tail_pointer(const struct sk_buff *skb)
{
        return skb->tail;
}

static inline void skb_reset_tail_pointer(struct sk_buff *skb)
{
        skb->tail = skb->data;
}

static inline void skb_set_tail_pointer(struct sk_buff *skb, const int offset)
{
        skb->tail = skb->data + offset;
}

#endif /* NET_SKBUFF_DATA_USES_OFFSET */

/*
 *      Add data to an sk_buff
 */
extern unsigned char *skb_put(struct sk_buff *skb, unsigned int len);
static inline unsigned char *__skb_put(struct sk_buff *skb, unsigned int len)
{
        unsigned char *tmp = skb_tail_pointer(skb);
        SKB_LINEAR_ASSERT(skb);
        skb->tail += len;
        skb->len  += len;
        return tmp;
}

extern unsigned char *skb_push(struct sk_buff *skb, unsigned int len);
static inline unsigned char *__skb_push(struct sk_buff *skb, unsigned int len)
{
        skb->data -= len;
        skb->len  += len;
        return skb->data;
}

extern unsigned char *skb_pull(struct sk_buff *skb, unsigned int len);
static inline unsigned char *__skb_pull(struct sk_buff *skb, unsigned int len)
{
        skb->len -= len;
        BUG_ON(skb->len < skb->data_len);
        return skb->data += len;
}

extern unsigned char *__pskb_pull_tail(struct sk_buff *skb, int delta);

static inline unsigned 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 unsigned 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, int len)
{
        skb->data += len;
        skb->tail += len;
}

#ifdef NET_SKBUFF_DATA_USES_OFFSET
static inline unsigned char *skb_transport_header(const struct sk_buff *skb)
{
        return skb->head + skb->transport_header;
}

static inline void skb_reset_transport_header(struct sk_buff *skb)
{
        skb->transport_header = skb->data - skb->head;
}

static inline void skb_set_transport_header(struct sk_buff *skb,
                                            const int offset)
{
        skb_reset_transport_header(skb);
        skb->transport_header += offset;
}

static inline unsigned char *skb_network_header(const struct sk_buff *skb)
{
        return skb->head + skb->network_header;
}

static inline void skb_reset_network_header(struct sk_buff *skb)
{
        skb->network_header = skb->data - skb->head;
}

static inline void skb_set_network_header(struct sk_buff *skb, const int offset)
{
        skb_reset_network_header(skb);
        skb->network_header += offset;
}

static inline unsigned char *skb_mac_header(const struct sk_buff *skb)
{
        return skb->head + skb->mac_header;
}

static inline int skb_mac_header_was_set(const struct sk_buff *skb)
{
        return skb->mac_header != ~0U;
}

static inline void skb_reset_mac_header(struct sk_buff *skb)
{
        skb->mac_header = skb->data - skb->head;
}

static inline void skb_set_mac_header(struct sk_buff *skb, const int offset)
{
        skb_reset_mac_header(skb);
        skb->mac_header += offset;
}

#else /* NET_SKBUFF_DATA_USES_OFFSET */

static inline unsigned char *skb_transport_header(const struct sk_buff *skb)
{
        return skb->transport_header;
}

static inline void skb_reset_transport_header(struct sk_buff *skb)
{
        skb->transport_header = skb->data;
}

static inline void skb_set_transport_header(struct sk_buff *skb,
                                            const int offset)
{
        skb->transport_header = skb->data + offset;
}

static inline unsigned char *skb_network_header(const struct sk_buff *skb)
{
        return skb->network_header;
}

static inline void skb_reset_network_header(struct sk_buff *skb)
{
        skb->network_header = skb->data;
}

static inline void skb_set_network_header(struct sk_buff *skb, const int offset)
{
        skb->network_header = skb->data + offset;
}

static inline unsigned char *skb_mac_header(const struct sk_buff *skb)
{
        return skb->mac_header;
}

static inline int skb_mac_header_was_set(const struct sk_buff *skb)
{
        return skb->mac_header != NULL;
}

static inline void skb_reset_mac_header(struct sk_buff *skb)
{
        skb->mac_header = skb->data;
}

static inline void skb_set_mac_header(struct sk_buff *skb, const int offset)
{
        skb->mac_header = skb->data + offset;
}
#endif /* NET_SKBUFF_DATA_USES_OFFSET */

static inline int skb_transport_offset(const struct sk_buff *skb)
{
        return skb_transport_header(skb) - skb->data;
}

static inline u32 skb_network_header_len(const struct sk_buff *skb)
{
        return skb->transport_header - skb->network_header;
}

static inline int skb_network_offset(const struct sk_buff *skb)
{
        return skb_network_header(skb) - skb->data;
}

/*
 * CPUs often take a performance hit when accessing unaligned memory
 * locations. The actual performance hit varies, it can be small if the
 * hardware handles it or large if we have to take an exception and fix it
 * in software.
 *
 * Since an ethernet header is 14 bytes network drivers often end up with
 * the IP header at an unaligned offset. The IP header can be aligned by
 * shifting the start of the packet by 2 bytes. Drivers should do this
 * with:
 *
 * skb_reserve(NET_IP_ALIGN);
 *
 * The downside to this alignment of the IP header is that the DMA is now
 * unaligned. On some architectures the cost of an unaligned DMA is high
 * and this cost outweighs the gains made by aligning the IP header.
 * 
 * Since this trade off varies between architectures, we allow NET_IP_ALIGN
 * to be overridden.
 */
#ifndef NET_IP_ALIGN
#define NET_IP_ALIGN    2
#endif

/*
 * The networking layer reserves some headroom in skb data (via
 * dev_alloc_skb). This is used to avoid having to reallocate skb data when
 * the header has to grow. In the default case, if the header has to grow
 * 32 bytes or less we avoid the reallocation.
 *
 * Unfortunately this headroom changes the DMA alignment of the resulting
 * network packet. As for NET_IP_ALIGN, this unaligned DMA is expensive
 * on some architectures. An architecture can override this value,
 * perhaps setting it to a cacheline in size (since that will maintain
 * cacheline alignment of the DMA). It must be a power of 2.
 *
 * Various parts of the networking layer expect at least 32 bytes of
 * headroom, you should not reduce this.
 */
#ifndef NET_SKB_PAD
#define NET_SKB_PAD     32
#endif

extern int ___pskb_trim(struct sk_buff *skb, unsigned int len);

static inline void __skb_trim(struct sk_buff *skb, unsigned int len)
{
        if (unlikely(skb->data_len)) {
                WARN_ON(1);
                return;
        }
        skb->len = len;
        skb_set_tail_pointer(skb, len);
}

extern void skb_trim(struct sk_buff *skb, unsigned int len);

static inline int __pskb_trim(struct sk_buff *skb, unsigned int len)
{
        if (skb->data_len)
                return ___pskb_trim(skb, len);
        __skb_trim(skb, len);
        return 0;
}

static inline int pskb_trim(struct sk_buff *skb, unsigned int len)
{
        return (len < skb->len) ? __pskb_trim(skb, len) : 0;
}

/**
 *      pskb_trim_unique - remove end from a paged unique (not cloned) buffer
 *      @skb: buffer to alter
 *      @len: new length
 *
 *      This is identical to pskb_trim except that the caller knows that
 *      the skb is not cloned so we should never get an error due to out-
 *      of-memory.
 */
static inline void pskb_trim_unique(struct sk_buff *skb, unsigned int len)
{
        int err = pskb_trim(skb, len);
        BUG_ON(err);
}

/**
 *      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 does not take the
 *      list lock and the caller must hold the relevant locks to use it.
 */
extern void skb_queue_purge(struct sk_buff_head *list);
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 receiving
 *      @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 if there is no free memory.
 */
static inline struct sk_buff *__dev_alloc_skb(unsigned int length,
                                              gfp_t gfp_mask)
{
        struct sk_buff *skb = alloc_skb(length + NET_SKB_PAD, gfp_mask);
        if (likely(skb))
                skb_reserve(skb, NET_SKB_PAD);
        return skb;
}

extern struct sk_buff *dev_alloc_skb(unsigned int length);

extern struct sk_buff *__netdev_alloc_skb(struct net_device *dev,
                unsigned int length, gfp_t gfp_mask);

/**
 *      netdev_alloc_skb - allocate an skbuff for rx on a specific device
 *      @dev: network device to receive on
 *      @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 if there is no free memory. Although this function
 *      allocates memory it can be called from an interrupt.
 */
static inline struct sk_buff *netdev_alloc_skb(struct net_device *dev,
                unsigned int length)
{
        return __netdev_alloc_skb(dev, length, GFP_ATOMIC);
}

extern struct page *__netdev_alloc_page(struct net_device *dev, gfp_t gfp_mask);

/**
 *      netdev_alloc_page - allocate a page for ps-rx on a specific device
 *      @dev: network device to receive on
 *
 *      Allocate a new page node local to the specified device.
 *
 *      %NULL is returned if there is no free memory.
 */
static inline struct page *netdev_alloc_page(struct net_device *dev)
{
        return __netdev_alloc_page(dev, GFP_ATOMIC);
}

static inline void netdev_free_page(struct net_device *dev, struct page *page)
{
        __free_page(page);
}

/**
 *      skb_clone_writable - is the header of a clone writable
 *      @skb: buffer to check
 *      @len: length up to which to write
 *
 *      Returns true if modifying the header part of the cloned buffer
 *      does not requires the data to be copied.
 */
static inline int skb_clone_writable(struct sk_buff *skb, unsigned int len)
{
        return !skb_header_cloned(skb) &&
               skb_headroom(skb) + len <= skb->hdr_len;
}

static inline int __skb_cow(struct sk_buff *skb, unsigned int headroom,
                            int cloned)
{
        int delta = 0;

        if (headroom < NET_SKB_PAD)
                headroom = NET_SKB_PAD;
        if (headroom > skb_headroom(skb))
                delta = headroom - skb_headroom(skb);

        if (delta || cloned)
                return pskb_expand_head(skb, ALIGN(delta, NET_SKB_PAD), 0,
                                        GFP_ATOMIC);
        return 0;
}

/**
 *      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)
{
        return __skb_cow(skb, headroom, skb_cloned(skb));
}

/**
 *      skb_cow_head - skb_cow but only making the head writable
 *      @skb: buffer to cow
 *      @headroom: needed headroom
 *
 *      This function is identical to skb_cow except that we replace the
 *      skb_cloned check by skb_header_cloned.  It should be used when
 *      you only need to push on some header and do not need to modify
 *      the data.
 */
static inline int skb_cow_head(struct sk_buff *skb, unsigned int headroom)
{
        return __skb_cow(skb, headroom, skb_header_cloned(skb));
}

/**
 *      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. Otherwise it is extended. Returns zero on
 *      success. The skb is freed on error.
 */
 
static inline int skb_padto(struct sk_buff *skb, unsigned int len)
{
        unsigned int size = skb->len;
        if (likely(size >= len))
                return 0;
        return skb_pad(skb, len - size);
}

static inline int skb_add_data(struct sk_buff *skb,
                               char __user *from, int copy)
{
        const int off = skb->len;

        if (skb->ip_summed == CHECKSUM_NONE) {
                int err = 0;
                __wsum csum = csum_and_copy_from_user(from, skb_put(skb, copy),
                                                            copy, 0, &err);
                if (!err) {
                        skb->csum = csum_block_add(skb->csum, csum, off);
                        return 0;
                }
        } else if (!copy_from_user(skb_put(skb, copy), from, copy))
                return 0;

        __skb_trim(skb, off);
        return -EFAULT;
}

static inline int skb_can_coalesce(struct sk_buff *skb, int i,
                                   struct page *page, int off)
{
        if (i) {
                struct skb_frag_struct *frag = &skb_shinfo(skb)->frags[i - 1];

                return page == frag->page &&
                       off == frag->page_offset + frag->size;
        }
        return 0;
}

static inline int __skb_linearize(struct sk_buff *skb)
{
        return __pskb_pull_tail(skb, skb->data_len) ? 0 : -ENOMEM;
}

/**
 *      skb_linearize - convert paged skb to linear one
 *      @skb: buffer to linarize
 *
 *      If there is no free memory -ENOMEM is returned, otherwise zero
 *      is returned and the old skb data released.
 */
static inline int skb_linearize(struct sk_buff *skb)
{
        return skb_is_nonlinear(skb) ? __skb_linearize(skb) : 0;
}

/**
 *      skb_linearize_cow - make sure skb is linear and writable
 *      @skb: buffer to process
 *
 *      If there is no free memory -ENOMEM is returned, otherwise zero
 *      is returned and the old skb data released.
 */
static inline int skb_linearize_cow(struct sk_buff *skb)
{
        return skb_is_nonlinear(skb) || skb_cloned(skb) ?
               __skb_linearize(skb) : 0;
}

/**
 *      skb_postpull_rcsum - update checksum for received skb after pull
 *      @skb: buffer to update
 *      @start: start of data before pull
 *      @len: length of data pulled
 *
 *      After doing a pull on a received packet, you need to call this to
 *      update the CHECKSUM_COMPLETE checksum, or set ip_summed to
 *      CHECKSUM_NONE so that it can be recomputed from scratch.
 */

static inline void skb_postpull_rcsum(struct sk_buff *skb,
                                      const void *start, unsigned int len)
{
        if (skb->ip_summed == CHECKSUM_COMPLETE)
                skb->csum = csum_sub(skb->csum, csum_partial(start, len, 0));
}

unsigned char *skb_pull_rcsum(struct sk_buff *skb, unsigned int len);

/**
 *      pskb_trim_rcsum - trim received skb and update checksum
 *      @skb: buffer to trim
 *      @len: new length
 *
 *      This is exactly the same as pskb_trim except that it ensures the
 *      checksum of received packets are still valid after the operation.
 */

static inline int pskb_trim_rcsum(struct sk_buff *skb, unsigned int len)
{
        if (likely(len >= skb->len))
                return 0;
        if (skb->ip_summed == CHECKSUM_COMPLETE)
                skb->ip_summed = CHECKSUM_NONE;
        return __pskb_trim(skb, len);
}

#define skb_queue_walk(queue, skb) \
                for (skb = (queue)->next;                                       \
                     prefetch(skb->next), (skb != (struct sk_buff *)(queue));   \
                     skb = skb->next)

#define skb_queue_walk_safe(queue, skb, tmp)                                    \
                for (skb = (queue)->next, tmp = skb->next;                      \
                     skb != (struct sk_buff *)(queue);                          \
                     skb = tmp, tmp = skb->next)

#define skb_queue_walk_from(queue, skb)                                         \
                for (; prefetch(skb->next), (skb != (struct sk_buff *)(queue)); \
                     skb = skb->next)

#define skb_queue_walk_from_safe(queue, skb, tmp)                               \
                for (tmp = skb->next;                                           \
                     skb != (struct sk_buff *)(queue);                          \
                     skb = tmp, tmp = skb->next)

#define skb_queue_reverse_walk(queue, skb) \
                for (skb = (queue)->prev;                                       \
                     prefetch(skb->prev), (skb != (struct sk_buff *)(queue));   \
                     skb = skb->prev)


extern struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned flags,
                                           int *peeked, int *err);
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_iovec(const struct sk_buff *from,
                                               int offset, struct iovec *to,
                                               int size);
extern int             skb_copy_and_csum_datagram_iovec(struct sk_buff *skb,
                                                        int hlen,
                                                        struct iovec *iov);
extern int             skb_copy_datagram_from_iovec(struct sk_buff *skb,
                                                    int offset,
                                                    const struct iovec *from,
                                                    int from_offset,
                                                    int len);
extern int             skb_copy_datagram_const_iovec(const struct sk_buff *from,
                                                     int offset,
                                                     const struct iovec *to,
                                                     int to_offset,
                                                     int size);
extern void            skb_free_datagram(struct sock *sk, struct sk_buff *skb);
extern int             skb_kill_datagram(struct sock *sk, struct sk_buff *skb,
                                         unsigned int flags);
extern __wsum          skb_checksum(const struct sk_buff *skb, int offset,
                                    int len, __wsum csum);
extern int             skb_copy_bits(const struct sk_buff *skb, int offset,
                                     void *to, int len);
extern int             skb_store_bits(struct sk_buff *skb, int offset,
                                      const void *from, int len);
extern __wsum          skb_copy_and_csum_bits(const struct sk_buff *skb,
                                              int offset, u8 *to, int len,
                                              __wsum csum);
extern int             skb_splice_bits(struct sk_buff *skb,
                                                unsigned int offset,
                                                struct pipe_inode_info *pipe,
                                                unsigned int len,
                                                unsigned int flags);
extern void            skb_copy_and_csum_dev(const struct sk_buff *skb, u8 *to);
extern void            skb_split(struct sk_buff *skb,
                                 struct sk_buff *skb1, const u32 len);
extern int             skb_shift(struct sk_buff *tgt, struct sk_buff *skb,
                                 int shiftlen);

extern struct sk_buff *skb_segment(struct sk_buff *skb, int features);

static inline void *skb_header_pointer(const struct sk_buff *skb, int offset,
                                       int len, void *buffer)
{
        int hlen = skb_headlen(skb);

        if (hlen - offset >= len)
                return skb->data + offset;

        if (skb_copy_bits(skb, offset, buffer, len) < 0)
                return NULL;

        return buffer;
}

static inline void skb_copy_from_linear_data(const struct sk_buff *skb,
                                             void *to,
                                             const unsigned int len)
{
        memcpy(to, skb->data, len);
}

static inline void skb_copy_from_linear_data_offset(const struct sk_buff *skb,
                                                    const int offset, void *to,
                                                    const unsigned int len)
{
        memcpy(to, skb->data + offset, len);
}

static inline void skb_copy_to_linear_data(struct sk_buff *skb,
                                           const void *from,
                                           const unsigned int len)
{
        memcpy(skb->data, from, len);
}

static inline void skb_copy_to_linear_data_offset(struct sk_buff *skb,
                                                  const int offset,
                                                  const void *from,
                                                  const unsigned int len)
{
        memcpy(skb->data + offset, from, len);
}

extern void skb_init(void);

static inline ktime_t skb_get_ktime(const struct sk_buff *skb)
{
        return skb->tstamp;
}

/**
 *      skb_get_timestamp - get timestamp from a skb
 *      @skb: skb to get stamp from
 *      @stamp: pointer to struct timeval to store stamp in
 *
 *      Timestamps are stored in the skb as offsets to a base timestamp.
 *      This function converts the offset back to a struct timeval and stores
 *      it in stamp.
 */
static inline void skb_get_timestamp(const struct sk_buff *skb,
                                     struct timeval *stamp)
{
        *stamp = ktime_to_timeval(skb->tstamp);
}

static inline void skb_get_timestampns(const struct sk_buff *skb,
                                       struct timespec *stamp)
{
        *stamp = ktime_to_timespec(skb->tstamp);
}

static inline void __net_timestamp(struct sk_buff *skb)
{
        skb->tstamp = ktime_get_real();
}

static inline ktime_t net_timedelta(ktime_t t)
{
        return ktime_sub(ktime_get_real(), t);
}

static inline ktime_t net_invalid_timestamp(void)
{
        return ktime_set(0, 0);
}

/**
 * skb_tstamp_tx - queue clone of skb with send time stamps
 * @orig_skb:   the original outgoing packet
 * @hwtstamps:  hardware time stamps, may be NULL if not available
 *
 * If the skb has a socket associated, then this function clones the
 * skb (thus sharing the actual data and optional structures), stores
 * the optional hardware time stamping information (if non NULL) or
 * generates a software time stamp (otherwise), then queues the clone
 * to the error queue of the socket.  Errors are silently ignored.
 */
extern void skb_tstamp_tx(struct sk_buff *orig_skb,
                        struct skb_shared_hwtstamps *hwtstamps);

extern __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len);
extern __sum16 __skb_checksum_complete(struct sk_buff *skb);

static inline int skb_csum_unnecessary(const struct sk_buff *skb)
{
        return skb->ip_summed & CHECKSUM_UNNECESSARY;
}

/**
 *      skb_checksum_complete - Calculate checksum of an entire packet
 *      @skb: packet to process
 *
 *      This function calculates the checksum over the entire packet plus
 *      the value of skb->csum.  The latter can be used to supply the
 *      checksum of a pseudo header as used by TCP/UDP.  It returns the
 *      checksum.
 *
 *      For protocols that contain complete checksums such as ICMP/TCP/UDP,
 *      this function can be used to verify that checksum on received
 *      packets.  In that case the function should return zero if the
 *      checksum is correct.  In particular, this function will return zero
 *      if skb->ip_summed is CHECKSUM_UNNECESSARY which indicates that the
 *      hardware has already verified the correctness of the checksum.
 */
static inline __sum16 skb_checksum_complete(struct sk_buff *skb)
{
        return skb_csum_unnecessary(skb) ?
               0 : __skb_checksum_complete(skb);
}

#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
extern void nf_conntrack_destroy(struct nf_conntrack *nfct);
static inline void nf_conntrack_put(struct nf_conntrack *nfct)
{
        if (nfct && atomic_dec_and_test(&nfct->use))
                nf_conntrack_destroy(nfct);
}
static inline void nf_conntrack_get(struct nf_conntrack *nfct)
{
        if (nfct)
                atomic_inc(&nfct->use);
}
static inline void nf_conntrack_get_reasm(struct sk_buff *skb)
{
        if (skb)
                atomic_inc(&skb->users);
}
static inline void nf_conntrack_put_reasm(struct sk_buff *skb)
{
        if (skb)
                kfree_skb(skb);
}
#endif
#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 /* CONFIG_BRIDGE_NETFILTER */
static inline void nf_reset(struct sk_buff *skb)
{
#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
        nf_conntrack_put(skb->nfct);
        skb->nfct = NULL;
        nf_conntrack_put_reasm(skb->nfct_reasm);
        skb->nfct_reasm = NULL;
#endif
#ifdef CONFIG_BRIDGE_NETFILTER
        nf_bridge_put(skb->nf_bridge);
        skb->nf_bridge = NULL;
#endif
}

/* Note: This doesn't put any conntrack and bridge info in dst. */
static inline void __nf_copy(struct sk_buff *dst, const struct sk_buff *src)
{
#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
        dst->nfct = src->nfct;
        nf_conntrack_get(src->nfct);
        dst->nfctinfo = src->nfctinfo;
        dst->nfct_reasm = src->nfct_reasm;
        nf_conntrack_get_reasm(src->nfct_reasm);
#endif
#ifdef CONFIG_BRIDGE_NETFILTER
        dst->nf_bridge  = src->nf_bridge;
        nf_bridge_get(src->nf_bridge);
#endif
}

static inline void nf_copy(struct sk_buff *dst, const struct sk_buff *src)
{
#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
        nf_conntrack_put(dst->nfct);
        nf_conntrack_put_reasm(dst->nfct_reasm);
#endif
#ifdef CONFIG_BRIDGE_NETFILTER
        nf_bridge_put(dst->nf_bridge);
#endif
        __nf_copy(dst, src);
}

#ifdef CONFIG_NETWORK_SECMARK
static inline void skb_copy_secmark(struct sk_buff *to, const struct sk_buff *from)
{
        to->secmark = from->secmark;
}

static inline void skb_init_secmark(struct sk_buff *skb)
{
        skb->secmark = 0;
}
#else
static inline void skb_copy_secmark(struct sk_buff *to, const struct sk_buff *from)
{ }

static inline void skb_init_secmark(struct sk_buff *skb)
{ }
#endif

static inline void skb_set_queue_mapping(struct sk_buff *skb, u16 queue_mapping)
{
        skb->queue_mapping = queue_mapping;
}

static inline u16 skb_get_queue_mapping(const struct sk_buff *skb)
{
        return skb->queue_mapping;
}

static inline void skb_copy_queue_mapping(struct sk_buff *to, const struct sk_buff *from)
{
        to->queue_mapping = from->queue_mapping;
}

static inline void skb_record_rx_queue(struct sk_buff *skb, u16 rx_queue)
{
        skb->queue_mapping = rx_queue + 1;
}

static inline u16 skb_get_rx_queue(const struct sk_buff *skb)
{
        return skb->queue_mapping - 1;
}

static inline bool skb_rx_queue_recorded(const struct sk_buff *skb)
{
        return (skb->queue_mapping != 0);
}

extern u16 skb_tx_hash(const struct net_device *dev,
                       const struct sk_buff *skb);

#ifdef CONFIG_XFRM
static inline struct sec_path *skb_sec_path(struct sk_buff *skb)
{
        return skb->sp;
}
#else
static inline struct sec_path *skb_sec_path(struct sk_buff *skb)
{
        return NULL;
}
#endif

static inline int skb_is_gso(const struct sk_buff *skb)
{
        return skb_shinfo(skb)->gso_size;
}

static inline int skb_is_gso_v6(const struct sk_buff *skb)
{
        return skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6;
}

extern void __skb_warn_lro_forwarding(const struct sk_buff *skb);

static inline bool skb_warn_if_lro(const struct sk_buff *skb)
{
        /* LRO sets gso_size but not gso_type, whereas if GSO is really
         * wanted then gso_type will be set. */
        struct skb_shared_info *shinfo = skb_shinfo(skb);
        if (shinfo->gso_size != 0 && unlikely(shinfo->gso_type == 0)) {
                __skb_warn_lro_forwarding(skb);
                return true;
        }
        return false;
}

static inline void skb_forward_csum(struct sk_buff *skb)
{
        /* Unfortunately we don't support this one.  Any brave souls? */
        if (skb->ip_summed == CHECKSUM_COMPLETE)
                skb->ip_summed = CHECKSUM_NONE;
}

bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off);
#endif  /* __KERNEL__ */
#endif  /* _LINUX_SKBUFF_H */