skbuff: size of hole is wrong in a comment

[~andy/linux] / 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/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>
#include <net/flow_keys.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 - 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;
};

/* 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,

        /* This indicates at least one fragment might be overwritten
         * (as in vmsplice(), sendfile() ...)
         * If we need to compute a TX checksum, we'll need to copy
         * all frags to avoid possible bad checksum
         */
        SKBTX_SHARED_FRAG = 1 << 5,
};

/*
 * 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 zerocopy_success argument is true if zero copy transmit occurred,
 * false on data copy or out of memory error caused by data copy attempt.
 * 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 *, bool zerocopy_success);
        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,

        SKB_GSO_GRE = 1 << 6,

        SKB_GSO_UDP_TUNNEL = 1 << 7,

        SKB_GSO_MPLS = 1 << 8,
};

#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 - socket buffer
 *      @next: Next buffer in list
 *      @prev: Previous buffer in list
 *      @tstamp: Time we arrived
 *      @sk: Socket we are owned by
 *      @dev: Device we arrived on/are leaving by
 *      @cb: Control buffer. Free for use by every layer. Put private vars here
 *      @_skb_refdst: destination entry (with norefcount bit)
 *      @sp: the security path, used for xfrm
 *      @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
 *      @priority: Packet queueing priority
 *      @local_df: allow local fragmentation
 *      @cloned: Head may be cloned (check refcnt to be sure)
 *      @ip_summed: Driver fed us an IP checksum
 *      @nohdr: Payload reference only, must not modify header
 *      @nfctinfo: Relationship of this skb to the connection
 *      @pkt_type: Packet class
 *      @fclone: skbuff clone status
 *      @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
 *      @protocol: Packet protocol from driver
 *      @destructor: Destruct function
 *      @nfct: Associated connection, if any
 *      @nfct_reasm: netfilter conntrack re-assembly pointer
 *      @nf_bridge: Saved data about a bridged frame - see br_netfilter.c
 *      @skb_iif: ifindex of device we arrived on
 *      @tc_index: Traffic control index
 *      @tc_verd: traffic control verdict
 *      @rxhash: the packet hash computed on receive
 *      @queue_mapping: Queue mapping for multiqueue devices
 *      @ndisc_nodetype: router type (from link layer)
 *      @ooo_okay: allow the mapping of a socket to a queue to be changed
 *      @l4_rxhash: indicate rxhash is a canonical 4-tuple hash over transport
 *              ports.
 *      @wifi_acked_valid: wifi_acked was set
 *      @wifi_acked: whether frame was acked on wifi or not
 *      @no_fcs:  Request NIC to treat last 4 bytes as Ethernet FCS
 *      @dma_cookie: a cookie to one of several possible DMA operations
 *              done by skb DMA functions
  *     @napi_id: id of the NAPI struct this skb came from
 *      @secmark: security marking
 *      @mark: Generic packet mark
 *      @dropcount: total number of sk_receive_queue overflows
 *      @vlan_proto: vlan encapsulation protocol
 *      @vlan_tci: vlan tag control information
 *      @inner_protocol: Protocol (encapsulation)
 *      @inner_transport_header: Inner transport layer header (encapsulation)
 *      @inner_network_header: Network layer header (encapsulation)
 *      @inner_mac_header: Link layer header (encapsulation)
 *      @transport_header: Transport layer header
 *      @network_header: Network layer header
 *      @mac_header: Link layer header
 *      @tail: Tail pointer
 *      @end: End pointer
 *      @head: Head of buffer
 *      @data: Data head pointer
 *      @truesize: Buffer size
 *      @users: User count - see {datagram,tcp}.c
 */

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;

        __be16                  vlan_proto;
        __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;
        /* Encapsulation protocol and NIC drivers should use
         * this flag to indicate to each other if the skb contains
         * encapsulated packet or not and maybe use the inner packet
         * headers if needed
         */
        __u8                    encapsulation:1;
        /* 6/8 bit hole (depending on ndisc_nodetype presence) */
        kmemcheck_bitfield_end(flags2);

#if defined CONFIG_NET_DMA || defined CONFIG_NET_RX_BUSY_POLL
        union {
                unsigned int    napi_id;
                dma_cookie_t    dma_cookie;
        };
#endif
#ifdef CONFIG_NETWORK_SECMARK
        __u32                   secmark;
#endif
        union {
                __u32           mark;
                __u32           dropcount;
                __u32           reserved_tailroom;
        };

        __be16                  inner_protocol;
        __u16                   inner_transport_header;
        __u16                   inner_network_header;
        __u16                   inner_mac_header;
        __u16                   transport_header;
        __u16                   network_header;
        __u16                   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)

/**
 * skb_dst - returns skb dst_entry
 * @skb: buffer
 *
 * Returns skb dst_entry, regardless of reference taken or not.
 */
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);
}

/**
 * skb_dst_set - sets skb dst
 * @skb: buffer
 * @dst: dst entry
 *
 * Sets skb dst, assuming a reference was taken on dst and should
 * be released by skb_dst_drop()
 */
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,
                                bool force);

/**
 * skb_dst_set_noref - sets skb dst, hopefully, without taking reference
 * @skb: buffer
 * @dst: dst entry
 *
 * Sets skb dst, assuming a reference was not taken on dst.
 * If dst entry is cached, we do not take reference and dst_release
 * will be avoided by refdst_drop. If dst entry is not cached, we take
 * reference, so that last dst_release can destroy the dst immediately.
 */
static inline void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
{
        __skb_dst_set_noref(skb, dst, false);
}

/**
 * skb_dst_set_noref_force - sets skb dst, without taking reference
 * @skb: buffer
 * @dst: dst entry
 *
 * Sets skb dst, assuming a reference was not taken on dst.
 * No reference is taken and no dst_release will be called. While for
 * cached dsts deferred reclaim is a basic feature, for entries that are
 * not cached it is caller's job to guarantee that last dst_release for
 * provided dst happens when nobody uses it, eg. after a RCU grace period.
 */
static inline void skb_dst_set_noref_force(struct sk_buff *skb,
                                           struct dst_entry *dst)
{
        __skb_dst_set_noref(skb, dst, true);
}

/**
 * skb_dst_is_noref - Test if skb dst isn't refcounted
 * @skb: buffer
 */
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 kfree_skb_list(struct sk_buff *segs);
extern void skb_tx_error(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 *__alloc_skb_head(gfp_t priority, int node);
static inline struct sk_buff *alloc_skb_head(gfp_t priority)
{
        return __alloc_skb_head(priority, -1);
}

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->l4_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;
}

/**
 *      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;
}

static inline int skb_unclone(struct sk_buff *skb, gfp_t pri)
{
        might_sleep_if(pri & __GFP_WAIT);

        if (skb_cloned(skb))
                return pskb_expand_head(skb, 0, 0, pri);

        return 0;
}

/**
 *      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);

                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.
 */

/**
 *      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 - peek at the head of an &sk_buff_head
 *      @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(const struct sk_buff_head *list_)
{
        struct sk_buff *skb = list_->next;

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

/**
 *      skb_peek_next - peek skb following the given one from a queue
 *      @skb: skb to start from
 *      @list_: list to peek at
 *
 *      Returns %NULL when the end of the list is met or a pointer to the
 *      next element. The reference count is not incremented and the
 *      reference is therefore volatile. Use with caution.
 */
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;
}

/**
 *      skb_peek_tail - peek at the tail of an &sk_buff_head
 *      @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(const struct sk_buff_head *list_)
{
        struct sk_buff *skb = list_->prev;

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

}

/**
 *      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_init - 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_init - 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 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);
}

/**
 * __skb_fill_page_desc - initialise a paged fragment in an skb
 * @skb: buffer containing fragment to be initialised
 * @i: paged fragment index to initialise
 * @page: the page to use for this fragment
 * @off: the offset to the data with @page
 * @size: the length of the data
 *
 * Initialises the @i'th fragment of @skb to point to &size bytes at
 * offset @off within @page.
 *
 * Does not take any additional reference on the fragment.
 */
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.
         */
        frag->page.p              = page;
        frag->page_offset         = off;
        skb_frag_size_set(frag, size);

        page = compound_head(page);
        if (page->pfmemalloc && !page->mapping)
                skb->pfmemalloc = true;
}

/**
 * skb_fill_page_desc - initialise a paged fragment in an skb
 * @skb: buffer containing fragment to be initialised
 * @i: paged fragment index to initialise
 * @page: the page to use for this fragment
 * @off: the offset to the data with @page
 * @size: the length of the data
 *
 * As per __skb_fill_page_desc() -- initialises the @i'th fragment of
 * @skb to point to &size bytes at offset @off within @page. In
 * addition updates @skb such that @i is the last fragment.
 *
 * Does not take any additional reference on the fragment.
 */
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;
}

/**
 *      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_availroom - bytes at buffer end
 *      @skb: buffer to check
 *
 *      Return the number of bytes of free space at the tail of an sk_buff
 *      allocated by sk_stream_alloc()
 */
static inline int skb_availroom(const struct sk_buff *skb)
{
        if (skb_is_nonlinear(skb))
                return 0;

        return skb->end - skb->tail - skb->reserved_tailroom;
}

/**
 *      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;
}

static inline void skb_reset_inner_headers(struct sk_buff *skb)
{
        skb->inner_mac_header = skb->mac_header;
        skb->inner_network_header = skb->network_header;
        skb->inner_transport_header = skb->transport_header;
}

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

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

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

static inline void skb_set_inner_transport_header(struct sk_buff *skb,
                                                   const int offset)
{
        skb_reset_inner_transport_header(skb);
        skb->inner_transport_header += offset;
}

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

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

static inline void skb_set_inner_network_header(struct sk_buff *skb,
                                                const int offset)
{
        skb_reset_inner_network_header(skb);
        skb->inner_network_header += offset;
}

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

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

static inline void skb_set_inner_mac_header(struct sk_buff *skb,
                                            const int offset)
{
        skb_reset_inner_mac_header(skb);
        skb->inner_mac_header += offset;
}
static inline bool skb_transport_header_was_set(const struct sk_buff *skb)
{
        return skb->transport_header != (typeof(skb->transport_header))~0U;
}

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 != (typeof(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;
}

static inline void skb_probe_transport_header(struct sk_buff *skb,
                                              const int offset_hint)
{
        struct flow_keys keys;

        if (skb_transport_header_was_set(skb))
                return;
        else if (skb_flow_dissect(skb, &keys))
                skb_set_transport_header(skb, keys.thoff);
        else
                skb_set_transport_header(skb, offset_hint);
}

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 u32 skb_inner_network_header_len(const struct sk_buff *skb)
{
        return skb->inner_transport_header - skb->inner_network_header;
}

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

static inline int skb_inner_network_offset(const struct sk_buff *skb)
{
        return skb_inner_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;
}

/**
 *      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;
        } else {
                BUG_ON(skb->sk);
        }
}

/**
 *      skb_orphan_frags - orphan the frags contained in a buffer
 *      @skb: buffer to orphan frags from
 *      @gfp_mask: allocation mask for replacement pages
 *
 *      For each frag in the SKB which needs a destructor (i.e. has an
 *      owner) create a copy of that frag and release the original
 *      page by calling the destructor.
 */
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);
}

/**
 *      __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);
}

#define NETDEV_FRAG_PAGE_MAX_ORDER get_order(32768)
#define NETDEV_FRAG_PAGE_MAX_SIZE  (PAGE_SIZE << NETDEV_FRAG_PAGE_MAX_ORDER)
#define NETDEV_PAGECNT_MAX_BIAS    NETDEV_FRAG_PAGE_MAX_SIZE

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);

/**
 *      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);
}

/* 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_pages - 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;
}

/**
 *      __skb_alloc_page - allocate a page for ps-rx for a given 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
 *
 *      Allocate a new page.
 *
 *      %NULL is returned if there is no free memory.
 */
static inline struct page *__skb_alloc_page(gfp_t gfp_mask,
                                             struct sk_buff *skb)
{
        return __skb_alloc_pages(gfp_mask, skb, 0);
}

/**
 *      skb_propagate_pfmemalloc - Propagate pfmemalloc if skb is allocated after RX page
 *      @page: The page that was allocated from skb_alloc_page
 *      @skb: The skb that may need pfmemalloc set
 */
static inline void skb_propagate_pfmemalloc(struct page *page,
                                             struct sk_buff *skb)
{
        if (page && page->pfmemalloc)
                skb->pfmemalloc = true;
}

/**
 * skb_frag_page - retrieve the page refered to by a paged fragment
 * @frag: the paged fragment
 *
 * Returns the &struct page associated with @frag.
 */
static inline struct page *skb_frag_page(const skb_frag_t *frag)
{
        return frag->page.p;
}

/**
 * __skb_frag_ref - take an addition reference on a paged fragment.
 * @frag: the paged fragment
 *
 * Takes an additional reference on the paged fragment @frag.
 */
static inline void __skb_frag_ref(skb_frag_t *frag)
{
        get_page(skb_frag_page(frag));
}

/**
 * skb_frag_ref - take an addition reference on a paged fragment of an skb.
 * @skb: the buffer
 * @f: the fragment offset.
 *
 * Takes an additional reference on the @f'th paged fragment of @skb.
 */
static inline void skb_frag_ref(struct sk_buff *skb, int f)
{
        __skb_frag_ref(&skb_shinfo(skb)->frags[f]);
}

/**
 * __skb_frag_unref - release a reference on a paged fragment.
 * @frag: the paged fragment
 *
 * Releases a reference on the paged fragment @frag.
 */
static inline void __skb_frag_unref(skb_frag_t *frag)
{
        put_page(skb_frag_page(frag));
}

/**
 * skb_frag_unref - release a reference on a paged fragment of an skb.
 * @skb: the buffer
 * @f: the fragment offset
 *
 * Releases a reference on the @f'th paged fragment of @skb.
 */
static inline void skb_frag_unref(struct sk_buff *skb, int f)
{
        __skb_frag_unref(&skb_shinfo(skb)->frags[f]);
}

/**
 * skb_frag_address - gets the address of the data contained in a paged fragment
 * @frag: the paged fragment buffer
 *
 * Returns the address of the data within @frag. The page must already
 * be mapped.
 */
static inline void *skb_frag_address(const skb_frag_t *frag)
{
        return page_address(skb_frag_page(frag)) + frag->page_offset;
}

/**
 * skb_frag_address_safe - gets the address of the data contained in a paged fragment
 * @frag: the paged fragment buffer
 *
 * Returns the address of the data within @frag. Checks that the page
 * is mapped and returns %NULL otherwise.
 */
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;
}

/**
 * __skb_frag_set_page - sets the page contained in a paged fragment
 * @frag: the paged fragment
 * @page: the page to set
 *
 * Sets the fragment @frag to contain @page.
 */
static inline void __skb_frag_set_page(skb_frag_t *frag, struct page *page)
{
        frag->page.p = page;
}

/**
 * skb_frag_set_page - sets the page contained in a paged fragment of an skb
 * @skb: the buffer
 * @f: the fragment offset
 * @page: the page to set
 *
 * Sets the @f'th fragment of @skb to contain @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);
}

/**
 * skb_frag_dma_map - maps a paged fragment via the DMA API
 * @dev: the device to map the fragment to
 * @frag: the paged fragment to map
 * @offset: the offset within the fragment (starting at the
 *          fragment's own offset)
 * @size: the number of bytes to map
 * @dir: the direction of the mapping (%PCI_DMA_*)
 *
 * Maps the page associated with @frag to @device.
 */
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);
}

/**
 *      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(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;
}

/**
 *      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 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;
}

/**
 *      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_has_shared_frag - can any frag be overwritten
 * @skb: buffer to test
 *
 * Return true if the skb has at least one frag that might be modified
 * by an external entity (as in vmsplice()/sendfile())
 */
static inline bool skb_has_shared_frag(const struct sk_buff *skb)
{
        return skb_is_nonlinear(skb) &&
               skb_shinfo(skb)->tx_flags & SKBTX_SHARED_FRAG;
}

/**
 *      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;                                       \
                     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             zerocopy_sg_from_iovec(struct sk_buff *skb,
                                              const struct iovec *frm,
                                              int offset,
                                              size_t count);
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 void            skb_scrub_packet(struct sk_buff *skb, bool xnet);

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;
}

/**
 *      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);
}

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 */

/**
 * skb_complete_tx_timestamp() - deliver cloned skb with tx timestamps
 *
 * PHY drivers may accept clones of transmitted packets for
 * timestamping via their phy_driver.txtstamp method. These drivers
 * must call this function to return the skb back to the stack, with
 * or without a timestamp.
 *
 * @skb: clone of the the original outgoing packet
 * @hwtstamps: hardware time stamps, may be NULL if not available
 *
 */
void skb_complete_tx_timestamp(struct sk_buff *skb,
                               struct skb_shared_hwtstamps *hwtstamps);

/**
 * 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);

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);
}

/**
 * skb_tx_timestamp() - Driver hook for transmit timestamping
 *
 * Ethernet MAC Drivers should call this function in their hard_xmit()
 * function immediately before giving the sk_buff to the MAC hardware.
 *
 * @skb: A socket buffer.
 */
static inline void skb_tx_timestamp(struct sk_buff *skb)
{
        skb_clone_tx_timestamp(skb);
        sw_tx_timestamp(skb);
}

/**
 * skb_complete_wifi_ack - deliver skb with wifi status
 *
 * @skb: the original outgoing packet
 * @acked: ack status
 *
 */
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;
}

/**
 *      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);
}
#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
}

static inline void nf_reset_trace(struct sk_buff *skb)
{
#if IS_ENABLED(CONFIG_NETFILTER_XT_TARGET_TRACE)
        skb->nf_trace = 0;
#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

/* Keeps track of mac header offset relative to skb->head.
 * It is useful for TSO of Tunneling protocol. e.g. GRE.
 * For non-tunnel skb it points to skb_mac_header() and for
 * tunnel skb it points to outer mac header. */
struct skb_gso_cb {
        int mac_offset;
};
#define SKB_GSO_CB(skb) ((struct skb_gso_cb *)(skb)->cb)

static inline int skb_tnl_header_len(const struct sk_buff *inner_skb)
{
        return (skb_mac_header(inner_skb) - inner_skb->head) -
                SKB_GSO_CB(inner_skb)->mac_offset;
}

static inline int gso_pskb_expand_head(struct sk_buff *skb, int extra)
{
        int new_headroom, headroom;
        int ret;

        headroom = skb_headroom(skb);
        ret = pskb_expand_head(skb, extra, 0, GFP_ATOMIC);
        if (ret)
                return ret;

        new_headroom = skb_headroom(skb);
        SKB_GSO_CB(skb)->mac_offset += (new_headroom - headroom);
        return 0;
}

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;
}

/**
 * skb_checksum_none_assert - make sure skb ip_summed is CHECKSUM_NONE
 * @skb: skb to check
 *
 * fresh skbs have their ip_summed set to CHECKSUM_NONE.
 * Instead of forcing ip_summed to CHECKSUM_NONE, we can
 * use this helper, to document places where we make this assertion.
 */
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);

u32 __skb_get_poff(const struct sk_buff *skb);

/**
 * skb_head_is_locked - Determine if the skb->head is locked down
 * @skb: skb to check
 *
 * The head on skbs build around a head frag can be removed if they are
 * not cloned.  This function returns true if the skb head is locked down
 * due to either being allocated via kmalloc, or by being a clone with
 * multiple references to the head.
 */
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 */