skbuff.h

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/*
 *  Definitions for the 'struct sk_buff' memory handlers.
 *
 *  Authors:
 *      Alan Cox, <[email protected]>
 *      Florian La Roche, <[email protected]>
 *
 *  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/kmemcheck.h>
#include <linux/compiler.h>
#include <linux/time.h>
#include <linux/bug.h>
#include <linux/cache.h>

#include <linux/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>
#include <linux/dma-mapping.h>
#include <linux/netdev_features.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))

/* return minimum truesize of one skb containing X bytes of data */
#define SKB_TRUESIZE(X) ((X) +                      \
             SKB_DATA_ALIGN(sizeof(struct sk_buff)) +   \
             SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))

/* 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_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.
 *
 *  UNNECESSARY: device will do per protocol specific csum. Protocol drivers
 *  that do not want net to perform the checksum calculation should use
 *  this flag in their outgoing skbs.
 *  NETIF_F_FCOE_CRC  this indicates the device can do FCoE FC CRC
 *            offload. Correspondingly, the FCoE protocol driver
 *            stack should use CHECKSUM_UNNECESSARY.
 *
 *  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;
    unsigned int        mask;
    struct net_device   *physindev;
    struct net_device   *physoutdev;
    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 we
 * require 64K/PAGE_SIZE pages plus 1 additional page to allow for
 * buffers which do not start on a page boundary.
 *
 * Since GRO uses frags we allocate at least 16 regardless of page
 * size.
 */
#if (65536/PAGE_SIZE + 1) < 16
#define MAX_SKB_FRAGS 16UL
#else
#define MAX_SKB_FRAGS (65536/PAGE_SIZE + 1)
#endif

typedef struct skb_frag_struct skb_frag_t;

struct skb_frag_struct {
    struct {
        struct page *p;
    } page;
#if (BITS_PER_LONG > 32) || (PAGE_SIZE >= 65536)
    __u32 page_offset;
    __u32 size;
#else
    __u16 page_offset;
    __u16 size;
#endif
};

static inline unsigned int skb_frag_size(const skb_frag_t *frag)
{
    return frag->size;
}

static inline void skb_frag_size_set(skb_frag_t *frag, unsigned int size)
{
    frag->size = size;
}

static inline void skb_frag_size_add(skb_frag_t *frag, int delta)
{
    frag->size += delta;
}

static inline void skb_frag_size_sub(skb_frag_t *frag, int delta)
{
    frag->size -= delta;
}

#define HAVE_HW_TIME_STAMP

struct skb_shared_hwtstamps {
    ktime_t hwtstamp;
    ktime_t syststamp;
};

/* Definitions for tx_flags in struct skb_shared_info */
enum {
    /* generate hardware time stamp */
    SKBTX_HW_TSTAMP = 1 << 0,

    /* generate software time stamp */
    SKBTX_SW_TSTAMP = 1 << 1,

    /* device driver is going to provide hardware time stamp */
    SKBTX_IN_PROGRESS = 1 << 2,

    /* device driver supports TX zero-copy buffers */
    SKBTX_DEV_ZEROCOPY = 1 << 3,

    /* generate wifi status information (where possible) */
    SKBTX_WIFI_STATUS = 1 << 4,
};

/*
 * The callback notifies userspace to release buffers when skb DMA is done in
 * lower device, the skb last reference should be 0 when calling this.
 * The ctx field is used to track device context.
 * The desc field is used to track userspace buffer index.
 */
struct ubuf_info {
    void (*callback)(struct ubuf_info *);
    void *ctx;
    unsigned long desc;
};

/* This data is invariant across clones and lives at
 * the end of the header data, ie. at skb->end.
 */
struct skb_shared_info {
    unsigned char   nr_frags;
    __u8        tx_flags;
    unsigned short  gso_size;
    /* Warning: this field is not always filled in (UFO)! */
    unsigned short  gso_segs;
    unsigned short  gso_type;
    struct sk_buff  *frag_list;
    struct skb_shared_hwtstamps hwtstamps;
    __be32          ip6_frag_id;

    /*
     * Warning : all fields before dataref are cleared in __alloc_skb()
     */
    atomic_t    dataref;

    /* Intermediate layers must ensure that destructor_arg
     * remains valid until skb destructor */
    void *      destructor_arg;

    /* must be last field, see pskb_expand_head() */
    skb_frag_t  frags[MAX_SKB_FRAGS];
};

/* 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

#if defined(CONFIG_NF_DEFRAG_IPV4) || defined(CONFIG_NF_DEFRAG_IPV4_MODULE) || \
    defined(CONFIG_NF_DEFRAG_IPV6) || defined(CONFIG_NF_DEFRAG_IPV6_MODULE)
#define NET_SKBUFF_NF_DEFRAG_NEEDED 1
#endif

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

    ktime_t         tstamp;

    struct sock     *sk;
    struct net_device   *dev;

    /*
     * 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] __aligned(8);

    unsigned long       _skb_refdst;
#ifdef CONFIG_XFRM
    struct  sec_path    *sp;
#endif
    unsigned int        len,
                data_len;
    __u16           mac_len,
                hdr_len;
    union {
        __wsum      csum;
        struct {
            __u16   csum_start;
            __u16   csum_offset;
        };
    };
    __u32           priority;
    kmemcheck_bitfield_begin(flags1);
    __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;
    kmemcheck_bitfield_end(flags1);
    __be16          protocol;

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

    int         skb_iif;

    __u32           rxhash;

    __u16           vlan_tci;

#ifdef CONFIG_NET_SCHED
    __u16           tc_index;   /* traffic control index */
#ifdef CONFIG_NET_CLS_ACT
    __u16           tc_verd;    /* traffic control verdict */
#endif
#endif

    __u16           queue_mapping;
    kmemcheck_bitfield_begin(flags2);
#ifdef CONFIG_IPV6_NDISC_NODETYPE
    __u8            ndisc_nodetype:2;
#endif
    __u8            pfmemalloc:1;
    __u8            ooo_okay:1;
    __u8            l4_rxhash:1;
    __u8            wifi_acked_valid:1;
    __u8            wifi_acked:1;
    __u8            no_fcs:1;
    __u8            head_frag:1;
    /* 8/10 bit hole (depending on ndisc_nodetype presence) */
    kmemcheck_bitfield_end(flags2);

#ifdef CONFIG_NET_DMA
    dma_cookie_t        dma_cookie;
#endif
#ifdef CONFIG_NETWORK_SECMARK
    __u32           secmark;
#endif
    union {
        __u32       mark;
        __u32       dropcount;
        __u32       avail_size;
    };

    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>


#define SKB_ALLOC_FCLONE    0x01
#define SKB_ALLOC_RX        0x02

/* Returns true if the skb was allocated from PFMEMALLOC reserves */
static inline bool skb_pfmemalloc(const struct sk_buff *skb)
{
    return unlikely(skb->pfmemalloc);
}

/*
 * skb might have a dst pointer attached, refcounted or not.
 * _skb_refdst low order bit is set if refcount was _not_ taken
 */
#define SKB_DST_NOREF   1UL
#define SKB_DST_PTRMASK ~(SKB_DST_NOREF)

static inline struct dst_entry *skb_dst(const struct sk_buff *skb)
{
    /* If refdst was not refcounted, check we still are in a 
     * rcu_read_lock section
     */
    WARN_ON((skb->_skb_refdst & SKB_DST_NOREF) &&
        !rcu_read_lock_held() &&
        !rcu_read_lock_bh_held());
    return (struct dst_entry *)(skb->_skb_refdst & SKB_DST_PTRMASK);
}

static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
{
    skb->_skb_refdst = (unsigned long)dst;
}

extern void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst);

static inline bool skb_dst_is_noref(const struct sk_buff *skb)
{
    return (skb->_skb_refdst & SKB_DST_NOREF) && skb_dst(skb);
}

static inline struct rtable *skb_rtable(const struct sk_buff *skb)
{
    return (struct rtable *)skb_dst(skb);
}

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 kmem_cache *skbuff_head_cache;

extern void kfree_skb_partial(struct sk_buff *skb, bool head_stolen);
extern bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
                 bool *fragstolen, int *delta_truesize);

extern struct sk_buff *__alloc_skb(unsigned int size,
                   gfp_t priority, int flags, int node);
extern struct sk_buff *build_skb(void *data, unsigned int frag_size);
static inline struct sk_buff *alloc_skb(unsigned int size,
                    gfp_t priority)
{
    return __alloc_skb(size, priority, 0, NUMA_NO_NODE);
}

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

extern struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src);
extern int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask);
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,
                 int headroom, 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)

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);

extern void __skb_get_rxhash(struct sk_buff *skb);
static inline __u32 skb_get_rxhash(struct sk_buff *skb)
{
    if (!skb->rxhash)
        __skb_get_rxhash(skb);

    return skb->rxhash;
}

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

static inline unsigned int skb_end_offset(const struct sk_buff *skb)
{
    return skb->end;
}
#else
static inline unsigned char *skb_end_pointer(const struct sk_buff *skb)
{
    return skb->end;
}

static inline unsigned int skb_end_offset(const struct sk_buff *skb)
{
    return skb->end - skb->head;
}
#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 int skb_queue_empty(const struct sk_buff_head *list)
{
    return list->next == (struct sk_buff *)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;
}

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;
}

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;
}

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;
}

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.
 */

static inline int skb_cloned(const struct sk_buff *skb)
{
    return skb->cloned &&
           (atomic_read(&skb_shinfo(skb)->dataref) & SKB_DATAREF_MASK) != 1;
}

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;
}

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);
}

static inline int skb_shared(const struct sk_buff *skb)
{
    return atomic_read(&skb->users) != 1;
}

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);

        if (likely(nskb))
            consume_skb(skb);
        else
            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.
 */

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;
}

static inline struct sk_buff *skb_peek(const struct sk_buff_head *list_)
{
    struct sk_buff *skb = list_->next;

    if (skb == (struct sk_buff *)list_)
        skb = NULL;
    return skb;
}

static inline struct sk_buff *skb_peek_next(struct sk_buff *skb,
        const struct sk_buff_head *list_)
{
    struct sk_buff *next = skb->next;

    if (next == (struct sk_buff *)list_)
        next = NULL;
    return next;
}

static inline struct sk_buff *skb_peek_tail(const struct sk_buff_head *list_)
{
    struct sk_buff *skb = list_->prev;

    if (skb == (struct sk_buff *)list_)
        skb = NULL;
    return skb;

}

static inline __u32 skb_queue_len(const struct sk_buff_head *list_)
{
    return list_->qlen;
}

static inline void __skb_queue_head_init(struct sk_buff_head *list)
{
    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;
}

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;
    }
}

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);
    }
}

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;
    }
}

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);
    }
}

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);
}

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);
}

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;
}

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;
}

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 bool 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_frag_size(&skb_shinfo(skb)->frags[i]);
    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];

    /*
     * Propagate page->pfmemalloc to the skb if we can. The problem is
     * that not all callers have unique ownership of the page. If
     * pfmemalloc is set, we check the mapping as a mapping implies
     * page->index is set (index and pfmemalloc share space).
     * If it's a valid mapping, we cannot use page->pfmemalloc but we
     * do not lose pfmemalloc information as the pages would not be
     * allocated using __GFP_MEMALLOC.
     */
    if (page->pfmemalloc && !page->mapping)
        skb->pfmemalloc = true;
    frag->page.p          = page;
    frag->page_offset     = off;
    skb_frag_size_set(frag, size);
}

static inline void skb_fill_page_desc(struct sk_buff *skb, int i,
                      struct page *page, int off, int size)
{
    __skb_fill_page_desc(skb, i, page, off, 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, unsigned int truesize);

#define SKB_PAGE_ASSERT(skb)    BUG_ON(skb_shinfo(skb)->nr_frags)
#define SKB_FRAG_ASSERT(skb)    BUG_ON(skb_has_frag_list(skb))
#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;
}

static inline unsigned char *skb_pull_inline(struct sk_buff *skb, unsigned int len)
{
    return unlikely(len > skb->len) ? NULL : __skb_pull(skb, len);
}

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

static inline 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;
}

static inline unsigned int skb_headroom(const struct sk_buff *skb)
{
    return skb->data - skb->head;
}

static inline int skb_tailroom(const struct sk_buff *skb)
{
    return skb_is_nonlinear(skb) ? 0 : skb->end - skb->tail;
}

static inline int skb_availroom(const struct sk_buff *skb)
{
    return skb_is_nonlinear(skb) ? 0 : skb->avail_size - skb->len;
}

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

static inline void skb_reset_mac_len(struct sk_buff *skb)
{
    skb->mac_len = skb->network_header - skb->mac_header;
}

#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 void skb_mac_header_rebuild(struct sk_buff *skb)
{
    if (skb_mac_header_was_set(skb)) {
        const unsigned char *old_mac = skb_mac_header(skb);

        skb_set_mac_header(skb, -skb->mac_len);
        memmove(skb_mac_header(skb), old_mac, skb->mac_len);
    }
}

static inline int skb_checksum_start_offset(const struct sk_buff *skb)
{
    return skb->csum_start - skb_headroom(skb);
}

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;
}

static inline int pskb_network_may_pull(struct sk_buff *skb, unsigned int len)
{
    return pskb_may_pull(skb, skb_network_offset(skb) + len);
}

/*
 * 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(skb, 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.
 *
 * Using max(32, L1_CACHE_BYTES) makes sense (especially with RPS)
 * to reduce average number of cache lines per packet.
 * get_rps_cpus() for example only access one 64 bytes aligned block :
 * NET_IP_ALIGN(2) + ethernet_header(14) + IP_header(20/40) + ports(8)
 */
#ifndef NET_SKB_PAD
#define NET_SKB_PAD max(32, L1_CACHE_BYTES)
#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_is_nonlinear(skb))) {
        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;
}

static inline void pskb_trim_unique(struct sk_buff *skb, unsigned int len)
{
    int err = pskb_trim(skb, len);
    BUG_ON(err);
}

static inline void skb_orphan(struct sk_buff *skb)
{
    if (skb->destructor)
        skb->destructor(skb);
    skb->destructor = NULL;
    skb->sk     = NULL;
}

static inline int skb_orphan_frags(struct sk_buff *skb, gfp_t gfp_mask)
{
    if (likely(!(skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY)))
        return 0;
    return skb_copy_ubufs(skb, gfp_mask);
}

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);
}

extern void *netdev_alloc_frag(unsigned int fragsz);

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

static inline struct sk_buff *netdev_alloc_skb(struct net_device *dev,
                           unsigned int length)
{
    return __netdev_alloc_skb(dev, length, GFP_ATOMIC);
}

/* legacy helper around __netdev_alloc_skb() */
static inline struct sk_buff *__dev_alloc_skb(unsigned int length,
                          gfp_t gfp_mask)
{
    return __netdev_alloc_skb(NULL, length, gfp_mask);
}

/* legacy helper around netdev_alloc_skb() */
static inline struct sk_buff *dev_alloc_skb(unsigned int length)
{
    return netdev_alloc_skb(NULL, length);
}


static inline struct sk_buff *__netdev_alloc_skb_ip_align(struct net_device *dev,
        unsigned int length, gfp_t gfp)
{
    struct sk_buff *skb = __netdev_alloc_skb(dev, length + NET_IP_ALIGN, gfp);

    if (NET_IP_ALIGN && skb)
        skb_reserve(skb, NET_IP_ALIGN);
    return skb;
}

static inline struct sk_buff *netdev_alloc_skb_ip_align(struct net_device *dev,
        unsigned int length)
{
    return __netdev_alloc_skb_ip_align(dev, length, GFP_ATOMIC);
}

/*
 *  __skb_alloc_page - allocate pages for ps-rx on a skb and preserve pfmemalloc data
 *  @gfp_mask: alloc_pages_node mask. Set __GFP_NOMEMALLOC if not for network packet RX
 *  @skb: skb to set pfmemalloc on if __GFP_MEMALLOC is used
 *  @order: size of the allocation
 *
 *  Allocate a new page.
 *
 *  %NULL is returned if there is no free memory.
*/
static inline struct page *__skb_alloc_pages(gfp_t gfp_mask,
                          struct sk_buff *skb,
                          unsigned int order)
{
    struct page *page;

    gfp_mask |= __GFP_COLD;

    if (!(gfp_mask & __GFP_NOMEMALLOC))
        gfp_mask |= __GFP_MEMALLOC;

    page = alloc_pages_node(NUMA_NO_NODE, gfp_mask, order);
    if (skb && page && page->pfmemalloc)
        skb->pfmemalloc = true;

    return page;
}

static inline struct page *__skb_alloc_page(gfp_t gfp_mask,
                         struct sk_buff *skb)
{
    return __skb_alloc_pages(gfp_mask, skb, 0);
}

static inline void skb_propagate_pfmemalloc(struct page *page,
                         struct sk_buff *skb)
{
    if (page && page->pfmemalloc)
        skb->pfmemalloc = true;
}

static inline struct page *skb_frag_page(const skb_frag_t *frag)
{
    return frag->page.p;
}

static inline void __skb_frag_ref(skb_frag_t *frag)
{
    get_page(skb_frag_page(frag));
}

static inline void skb_frag_ref(struct sk_buff *skb, int f)
{
    __skb_frag_ref(&skb_shinfo(skb)->frags[f]);
}

static inline void __skb_frag_unref(skb_frag_t *frag)
{
    put_page(skb_frag_page(frag));
}

static inline void skb_frag_unref(struct sk_buff *skb, int f)
{
    __skb_frag_unref(&skb_shinfo(skb)->frags[f]);
}

static inline void *skb_frag_address(const skb_frag_t *frag)
{
    return page_address(skb_frag_page(frag)) + frag->page_offset;
}

static inline void *skb_frag_address_safe(const skb_frag_t *frag)
{
    void *ptr = page_address(skb_frag_page(frag));
    if (unlikely(!ptr))
        return NULL;

    return ptr + frag->page_offset;
}

static inline void __skb_frag_set_page(skb_frag_t *frag, struct page *page)
{
    frag->page.p = page;
}

static inline void skb_frag_set_page(struct sk_buff *skb, int f,
                     struct page *page)
{
    __skb_frag_set_page(&skb_shinfo(skb)->frags[f], page);
}

static inline dma_addr_t skb_frag_dma_map(struct device *dev,
                      const skb_frag_t *frag,
                      size_t offset, size_t size,
                      enum dma_data_direction dir)
{
    return dma_map_page(dev, skb_frag_page(frag),
                frag->page_offset + offset, size, dir);
}

static inline struct sk_buff *pskb_copy(struct sk_buff *skb,
                    gfp_t gfp_mask)
{
    return __pskb_copy(skb, skb_headroom(skb), gfp_mask);
}

static inline int skb_clone_writable(const 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 > 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;
}

static inline int skb_cow(struct sk_buff *skb, unsigned int headroom)
{
    return __skb_cow(skb, headroom, skb_cloned(skb));
}

static inline int skb_cow_head(struct sk_buff *skb, unsigned int headroom)
{
    return __skb_cow(skb, headroom, skb_header_cloned(skb));
}

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

        return page == skb_frag_page(frag) &&
               off == frag->page_offset + skb_frag_size(frag);
    }
    return false;
}

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

static inline int skb_linearize(struct sk_buff *skb)
{
    return skb_is_nonlinear(skb) ? __skb_linearize(skb) : 0;
}

static inline int skb_linearize_cow(struct sk_buff *skb)
{
    return skb_is_nonlinear(skb) || skb_cloned(skb) ?
           __skb_linearize(skb) : 0;
}

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);

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;                   \
             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 (; 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;                   \
             skb != (struct sk_buff *)(queue);              \
             skb = skb->prev)

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

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

static inline bool skb_has_frag_list(const struct sk_buff *skb)
{
    return skb_shinfo(skb)->frag_list != NULL;
}

static inline void skb_frag_list_init(struct sk_buff *skb)
{
    skb_shinfo(skb)->frag_list = NULL;
}

static inline void skb_frag_add_head(struct sk_buff *skb, struct sk_buff *frag)
{
    frag->next = skb_shinfo(skb)->frag_list;
    skb_shinfo(skb)->frag_list = frag;
}

#define skb_walk_frags(skb, iter)   \
    for (iter = skb_shinfo(skb)->frag_list; iter; iter = iter->next)

extern struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned flags,
                       int *peeked, int *off, 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 void        skb_free_datagram_locked(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,
                   netdev_features_t 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;
}

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);
}

extern void skb_timestamping_init(void);

#ifdef CONFIG_NETWORK_PHY_TIMESTAMPING

extern void skb_clone_tx_timestamp(struct sk_buff *skb);
extern bool skb_defer_rx_timestamp(struct sk_buff *skb);

#else /* CONFIG_NETWORK_PHY_TIMESTAMPING */

static inline void skb_clone_tx_timestamp(struct sk_buff *skb)
{
}

static inline bool skb_defer_rx_timestamp(struct sk_buff *skb)
{
    return false;
}

#endif /* !CONFIG_NETWORK_PHY_TIMESTAMPING */

void skb_complete_tx_timestamp(struct sk_buff *skb,
                   struct skb_shared_hwtstamps *hwtstamps);

extern void skb_tstamp_tx(struct sk_buff *orig_skb,
            struct skb_shared_hwtstamps *hwtstamps);

static inline void sw_tx_timestamp(struct sk_buff *skb)
{
    if (skb_shinfo(skb)->tx_flags & SKBTX_SW_TSTAMP &&
        !(skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS))
        skb_tstamp_tx(skb, NULL);
}

static inline void skb_tx_timestamp(struct sk_buff *skb)
{
    skb_clone_tx_timestamp(skb);
    sw_tx_timestamp(skb);
}

void skb_complete_wifi_ack(struct sk_buff *skb, bool acked);

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;
}

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);
}
#endif
#ifdef NET_SKBUFF_NF_DEFRAG_NEEDED
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;
#endif
#ifdef NET_SKBUFF_NF_DEFRAG_NEEDED
    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;
#endif
#ifdef NET_SKBUFF_NF_DEFRAG_NEEDED
    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);
#endif
#ifdef NET_SKBUFF_NF_DEFRAG_NEEDED
    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,
             unsigned int num_tx_queues);

#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 bool skb_is_gso(const struct sk_buff *skb)
{
    return skb_shinfo(skb)->gso_size;
}

static inline bool 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. */
    const struct skb_shared_info *shinfo = skb_shinfo(skb);

    if (skb_is_nonlinear(skb) && 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;
}

static inline void skb_checksum_none_assert(const struct sk_buff *skb)
{
#ifdef DEBUG
    BUG_ON(skb->ip_summed != CHECKSUM_NONE);
#endif
}

bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off);

static inline bool skb_head_is_locked(const struct sk_buff *skb)
{
    return !skb->head_frag || skb_cloned(skb);
}
#endif  /* __KERNEL__ */
#endif  /* _LINUX_SKBUFF_H */