Merge tag 'stackleak-v4.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git...

[sfrench/cifs-2.6.git] / include / linux / skbuff.h

/*
 *      Definitions for the 'struct sk_buff' memory handlers.
 *
 *      Authors:
 *              Alan Cox, <gw4pts@gw4pts.ampr.org>
 *              Florian La Roche, <rzsfl@rz.uni-sb.de>
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 */

#ifndef _LINUX_SKBUFF_H
#define _LINUX_SKBUFF_H

#include <linux/kernel.h>
#include <linux/compiler.h>
#include <linux/time.h>
#include <linux/bug.h>
#include <linux/cache.h>
#include <linux/rbtree.h>
#include <linux/socket.h>
#include <linux/refcount.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/hrtimer.h>
#include <linux/dma-mapping.h>
#include <linux/netdev_features.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
#include <net/flow_dissector.h>
#include <linux/splice.h>
#include <linux/in6.h>
#include <linux/if_packet.h>
#include <net/flow.h>

/* The interface for checksum offload between the stack and networking drivers
 * is as follows...
 *
 * A. IP checksum related features
 *
 * Drivers advertise checksum offload capabilities in the features of a device.
 * From the stack's point of view these are capabilities offered by the driver,
 * a driver typically only advertises features that it is capable of offloading
 * to its device.
 *
 * The checksum related features are:
 *
 *      NETIF_F_HW_CSUM - The driver (or its device) is able to compute one
 *                        IP (one's complement) checksum for any combination
 *                        of protocols or protocol layering. The checksum is
 *                        computed and set in a packet per the CHECKSUM_PARTIAL
 *                        interface (see below).
 *
 *      NETIF_F_IP_CSUM - Driver (device) is only able to checksum plain
 *                        TCP or UDP packets over IPv4. These are specifically
 *                        unencapsulated packets of the form IPv4|TCP or
 *                        IPv4|UDP where the Protocol field in the IPv4 header
 *                        is TCP or UDP. The IPv4 header may contain IP options
 *                        This feature cannot be set in features for a device
 *                        with NETIF_F_HW_CSUM also set. This feature is being
 *                        DEPRECATED (see below).
 *
 *      NETIF_F_IPV6_CSUM - Driver (device) is only able to checksum plain
 *                        TCP or UDP packets over IPv6. These are specifically
 *                        unencapsulated packets of the form IPv6|TCP or
 *                        IPv4|UDP where the Next Header field in the IPv6
 *                        header is either TCP or UDP. IPv6 extension headers
 *                        are not supported with this feature. This feature
 *                        cannot be set in features for a device with
 *                        NETIF_F_HW_CSUM also set. This feature is being
 *                        DEPRECATED (see below).
 *
 *      NETIF_F_RXCSUM - Driver (device) performs receive checksum offload.
 *                       This flag is used only used to disable the RX checksum
 *                       feature for a device. The stack will accept receive
 *                       checksum indication in packets received on a device
 *                       regardless of whether NETIF_F_RXCSUM is set.
 *
 * B. Checksumming of received packets by device. Indication of checksum
 *    verification is in set skb->ip_summed. Possible values are:
 *
 * CHECKSUM_NONE:
 *
 *   Device did not checksum this packet e.g. due to lack of capabilities.
 *   The packet contains full (though not verified) checksum in packet but
 *   not in skb->csum. Thus, skb->csum is undefined in this case.
 *
 * CHECKSUM_UNNECESSARY:
 *
 *   The hardware you're dealing with doesn't calculate the full checksum
 *   (as in CHECKSUM_COMPLETE), but it does parse headers and verify checksums
 *   for specific protocols. For such packets it will set CHECKSUM_UNNECESSARY
 *   if their checksums are okay. skb->csum is still undefined in this case
 *   though. A driver or device must never modify the checksum field in the
 *   packet even if checksum is verified.
 *
 *   CHECKSUM_UNNECESSARY is applicable to following protocols:
 *     TCP: IPv6 and IPv4.
 *     UDP: IPv4 and IPv6. A device may apply CHECKSUM_UNNECESSARY to a
 *       zero UDP checksum for either IPv4 or IPv6, the networking stack
 *       may perform further validation in this case.
 *     GRE: only if the checksum is present in the header.
 *     SCTP: indicates the CRC in SCTP header has been validated.
 *     FCOE: indicates the CRC in FC frame has been validated.
 *
 *   skb->csum_level indicates the number of consecutive checksums found in
 *   the packet minus one that have been verified as CHECKSUM_UNNECESSARY.
 *   For instance if a device receives an IPv6->UDP->GRE->IPv4->TCP packet
 *   and a device is able to verify the checksums for UDP (possibly zero),
 *   GRE (checksum flag is set), and TCP-- skb->csum_level would be set to
 *   two. If the device were only able to verify the UDP checksum and not
 *   GRE, either because it doesn't support GRE checksum of because GRE
 *   checksum is bad, skb->csum_level would be set to zero (TCP checksum is
 *   not considered in this case).
 *
 * CHECKSUM_COMPLETE:
 *
 *   This is the most generic way. The device supplied checksum of the _whole_
 *   packet as seen by netif_rx() and fills out in skb->csum. Meaning, the
 *   hardware doesn't need to parse L3/L4 headers to implement this.
 *
 *   Notes:
 *   - Even if device supports only some protocols, but is able to produce
 *     skb->csum, it MUST use CHECKSUM_COMPLETE, not CHECKSUM_UNNECESSARY.
 *   - CHECKSUM_COMPLETE is not applicable to SCTP and FCoE protocols.
 *
 * CHECKSUM_PARTIAL:
 *
 *   A checksum is set up to be offloaded to a device as described in the
 *   output description for CHECKSUM_PARTIAL. This may occur on a packet
 *   received directly from another Linux OS, e.g., a virtualized Linux kernel
 *   on the same host, or it may be set in the input path in GRO or remote
 *   checksum offload. For the purposes of checksum verification, the checksum
 *   referred to by skb->csum_start + skb->csum_offset and any preceding
 *   checksums in the packet are considered verified. Any checksums in the
 *   packet that are after the checksum being offloaded are not considered to
 *   be verified.
 *
 * C. Checksumming on transmit for non-GSO. The stack requests checksum offload
 *    in the skb->ip_summed for a packet. Values are:
 *
 * CHECKSUM_PARTIAL:
 *
 *   The driver is required to checksum the packet as seen by hard_start_xmit()
 *   from skb->csum_start up to the end, and to record/write the checksum at
 *   offset skb->csum_start + skb->csum_offset. A driver may verify that the
 *   csum_start and csum_offset values are valid values given the length and
 *   offset of the packet, however they should not attempt to validate that the
 *   checksum refers to a legitimate transport layer checksum-- it is the
 *   purview of the stack to validate that csum_start and csum_offset are set
 *   correctly.
 *
 *   When the stack requests checksum offload for a packet, the driver MUST
 *   ensure that the checksum is set correctly. A driver can either offload the
 *   checksum calculation to the device, or call skb_checksum_help (in the case
 *   that the device does not support offload for a particular checksum).
 *
 *   NETIF_F_IP_CSUM and NETIF_F_IPV6_CSUM are being deprecated in favor of
 *   NETIF_F_HW_CSUM. New devices should use NETIF_F_HW_CSUM to indicate
 *   checksum offload capability.
 *   skb_csum_hwoffload_help() can be called to resolve CHECKSUM_PARTIAL based
 *   on network device checksumming capabilities: if a packet does not match
 *   them, skb_checksum_help or skb_crc32c_help (depending on the value of
 *   csum_not_inet, see item D.) is called to resolve the checksum.
 *
 * CHECKSUM_NONE:
 *
 *   The skb was already checksummed by the protocol, or a checksum is not
 *   required.
 *
 * CHECKSUM_UNNECESSARY:
 *
 *   This has the same meaning on as CHECKSUM_NONE for checksum offload on
 *   output.
 *
 * CHECKSUM_COMPLETE:
 *   Not used in checksum output. If a driver observes a packet with this value
 *   set in skbuff, if should treat as CHECKSUM_NONE being set.
 *
 * D. Non-IP checksum (CRC) offloads
 *
 *   NETIF_F_SCTP_CRC - This feature indicates that a device is capable of
 *     offloading the SCTP CRC in a packet. To perform this offload the stack
 *     will set set csum_start and csum_offset accordingly, set ip_summed to
 *     CHECKSUM_PARTIAL and set csum_not_inet to 1, to provide an indication in
 *     the skbuff that the CHECKSUM_PARTIAL refers to CRC32c.
 *     A driver that supports both IP checksum offload and SCTP CRC32c offload
 *     must verify which offload is configured for a packet by testing the
 *     value of skb->csum_not_inet; skb_crc32c_csum_help is provided to resolve
 *     CHECKSUM_PARTIAL on skbs where csum_not_inet is set to 1.
 *
 *   NETIF_F_FCOE_CRC - This feature indicates that a device is capable of
 *     offloading the FCOE CRC in a packet. To perform this offload the stack
 *     will set ip_summed to CHECKSUM_PARTIAL and set csum_start and csum_offset
 *     accordingly. Note the there is no indication in the skbuff that the
 *     CHECKSUM_PARTIAL refers to an FCOE checksum, a driver that supports
 *     both IP checksum offload and FCOE CRC offload must verify which offload
 *     is configured for a packet presumably by inspecting packet headers.
 *
 * E. Checksumming on output with GSO.
 *
 * In the case of a GSO packet (skb_is_gso(skb) is true), checksum offload
 * is implied by the SKB_GSO_* flags in gso_type. Most obviously, if the
 * gso_type is SKB_GSO_TCPV4 or SKB_GSO_TCPV6, TCP checksum offload as
 * part of the GSO operation is implied. If a checksum is being offloaded
 * with GSO then ip_summed is CHECKSUM_PARTIAL, csum_start and csum_offset
 * are set to refer to the outermost checksum being offload (two offloaded
 * checksums are possible with UDP encapsulation).
 */

/* 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

/* Maximum value in skb->csum_level */
#define SKB_MAX_CSUM_LEVEL      3

#define SKB_DATA_ALIGN(X)       ALIGN(X, SMP_CACHE_BYTES)
#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)))

struct net_device;
struct scatterlist;
struct pipe_inode_info;
struct iov_iter;
struct napi_struct;
struct bpf_prog;
union bpf_attr;

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

#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
struct nf_bridge_info {
        refcount_t              use;
        enum {
                BRNF_PROTO_UNCHANGED,
                BRNF_PROTO_8021Q,
                BRNF_PROTO_PPPOE
        } orig_proto:8;
        u8                      pkt_otherhost:1;
        u8                      in_prerouting:1;
        u8                      bridged_dnat:1;
        __u16                   frag_max_size;
        struct net_device       *physindev;

        /* always valid & non-NULL from FORWARD on, for physdev match */
        struct net_device       *physoutdev;
        union {
                /* prerouting: detect dnat in orig/reply direction */
                __be32          ipv4_daddr;
                struct in6_addr ipv6_daddr;

                /* after prerouting + nat detected: store original source
                 * mac since neigh resolution overwrites it, only used while
                 * skb is out in neigh layer.
                 */
                char neigh_header[8];
        };
};
#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
extern int sysctl_max_skb_frags;

/* Set skb_shinfo(skb)->gso_size to this in case you want skb_segment to
 * segment using its current segmentation instead.
 */
#define GSO_BY_FRAGS    0xFFFF

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;
}

static inline bool skb_frag_must_loop(struct page *p)
{
#if defined(CONFIG_HIGHMEM)
        if (PageHighMem(p))
                return true;
#endif
        return false;
}

/**
 *      skb_frag_foreach_page - loop over pages in a fragment
 *
 *      @f:             skb frag to operate on
 *      @f_off:         offset from start of f->page.p
 *      @f_len:         length from f_off to loop over
 *      @p:             (temp var) current page
 *      @p_off:         (temp var) offset from start of current page,
 *                                 non-zero only on first page.
 *      @p_len:         (temp var) length in current page,
 *                                 < PAGE_SIZE only on first and last page.
 *      @copied:        (temp var) length so far, excluding current p_len.
 *
 *      A fragment can hold a compound page, in which case per-page
 *      operations, notably kmap_atomic, must be called for each
 *      regular page.
 */
#define skb_frag_foreach_page(f, f_off, f_len, p, p_off, p_len, copied) \
        for (p = skb_frag_page(f) + ((f_off) >> PAGE_SHIFT),            \
             p_off = (f_off) & (PAGE_SIZE - 1),                         \
             p_len = skb_frag_must_loop(p) ?                            \
             min_t(u32, f_len, PAGE_SIZE - p_off) : f_len,              \
             copied = 0;                                                \
             copied < f_len;                                            \
             copied += p_len, p++, p_off = 0,                           \
             p_len = min_t(u32, f_len - copied, PAGE_SIZE))             \

#define HAVE_HW_TIME_STAMP

/**
 * struct skb_shared_hwtstamps - hardware time stamps
 * @hwtstamp:   hardware time stamp transformed into duration
 *              since arbitrary point in time
 *
 * Software time stamps generated by ktime_get_real() are stored in
 * skb->tstamp.
 *
 * 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;
};

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

        /* generate software time stamp when queueing packet to NIC */
        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,

        /* generate software time stamp when entering packet scheduling */
        SKBTX_SCHED_TSTAMP = 1 << 6,
};

#define SKBTX_ZEROCOPY_FRAG     (SKBTX_DEV_ZEROCOPY | SKBTX_SHARED_FRAG)
#define SKBTX_ANY_SW_TSTAMP     (SKBTX_SW_TSTAMP    | \
                                 SKBTX_SCHED_TSTAMP)
#define SKBTX_ANY_TSTAMP        (SKBTX_HW_TSTAMP | SKBTX_ANY_SW_TSTAMP)

/*
 * 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);
        union {
                struct {
                        unsigned long desc;
                        void *ctx;
                };
                struct {
                        u32 id;
                        u16 len;
                        u16 zerocopy:1;
                        u32 bytelen;
                };
        };
        refcount_t refcnt;

        struct mmpin {
                struct user_struct *user;
                unsigned int num_pg;
        } mmp;
};

#define skb_uarg(SKB)   ((struct ubuf_info *)(skb_shinfo(SKB)->destructor_arg))

int mm_account_pinned_pages(struct mmpin *mmp, size_t size);
void mm_unaccount_pinned_pages(struct mmpin *mmp);

struct ubuf_info *sock_zerocopy_alloc(struct sock *sk, size_t size);
struct ubuf_info *sock_zerocopy_realloc(struct sock *sk, size_t size,
                                        struct ubuf_info *uarg);

static inline void sock_zerocopy_get(struct ubuf_info *uarg)
{
        refcount_inc(&uarg->refcnt);
}

void sock_zerocopy_put(struct ubuf_info *uarg);
void sock_zerocopy_put_abort(struct ubuf_info *uarg);

void sock_zerocopy_callback(struct ubuf_info *uarg, bool success);

int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb,
                             struct msghdr *msg, int len,
                             struct ubuf_info *uarg);

/* This data is invariant across clones and lives at
 * the end of the header data, ie. at skb->end.
 */
struct skb_shared_info {
        __u8            __unused;
        __u8            meta_len;
        __u8            nr_frags;
        __u8            tx_flags;
        unsigned short  gso_size;
        /* Warning: this field is not always filled in (UFO)! */
        unsigned short  gso_segs;
        struct sk_buff  *frag_list;
        struct skb_shared_hwtstamps hwtstamps;
        unsigned int    gso_type;
        u32             tskey;

        /*
         * 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 has no fclone (from head_cache) */
        SKB_FCLONE_ORIG,        /* orig skb (from fclone_cache) */
        SKB_FCLONE_CLONE,       /* companion fclone skb (from fclone_cache) */
};

enum {
        SKB_GSO_TCPV4 = 1 << 0,

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

        /* This indicates the tcp segment has CWR set. */
        SKB_GSO_TCP_ECN = 1 << 2,

        SKB_GSO_TCP_FIXEDID = 1 << 3,

        SKB_GSO_TCPV6 = 1 << 4,

        SKB_GSO_FCOE = 1 << 5,

        SKB_GSO_GRE = 1 << 6,

        SKB_GSO_GRE_CSUM = 1 << 7,

        SKB_GSO_IPXIP4 = 1 << 8,

        SKB_GSO_IPXIP6 = 1 << 9,

        SKB_GSO_UDP_TUNNEL = 1 << 10,

        SKB_GSO_UDP_TUNNEL_CSUM = 1 << 11,

        SKB_GSO_PARTIAL = 1 << 12,

        SKB_GSO_TUNNEL_REMCSUM = 1 << 13,

        SKB_GSO_SCTP = 1 << 14,

        SKB_GSO_ESP = 1 << 15,

        SKB_GSO_UDP = 1 << 16,

        SKB_GSO_UDP_L4 = 1 << 17,
};

#if BITS_PER_LONG > 32
#define NET_SKBUFF_DATA_USES_OFFSET 1
#endif

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

/** 
 *      struct sk_buff - socket buffer
 *      @next: Next buffer in list
 *      @prev: Previous buffer in list
 *      @tstamp: Time we arrived/left
 *      @rbnode: RB tree node, alternative to next/prev for netem/tcp
 *      @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
 *      @ignore_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
 *      @pkt_type: Packet class
 *      @fclone: skbuff clone status
 *      @ipvs_property: skbuff is owned by ipvs
 *      @tc_skip_classify: do not classify packet. set by IFB device
 *      @tc_at_ingress: used within tc_classify to distinguish in/egress
 *      @tc_redirected: packet was redirected by a tc action
 *      @tc_from_ingress: if tc_redirected, tc_at_ingress at time of redirect
 *      @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
 *      @tcp_tsorted_anchor: list structure for TCP (tp->tsorted_sent_queue)
 *      @_nfct: Associated connection, if any (with nfctinfo bits)
 *      @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
 *      @hash: the packet hash
 *      @queue_mapping: Queue mapping for multiqueue devices
 *      @xmit_more: More SKBs are pending for this queue
 *      @pfmemalloc: skbuff was allocated from PFMEMALLOC reserves
 *      @ndisc_nodetype: router type (from link layer)
 *      @ooo_okay: allow the mapping of a socket to a queue to be changed
 *      @l4_hash: indicate hash is a canonical 4-tuple hash over transport
 *              ports.
 *      @sw_hash: indicates hash was computed in software stack
 *      @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
 *      @csum_not_inet: use CRC32c to resolve CHECKSUM_PARTIAL
 *      @dst_pending_confirm: need to confirm neighbour
 *      @decrypted: Decrypted SKB
  *     @napi_id: id of the NAPI struct this skb came from
 *      @secmark: security marking
 *      @mark: Generic packet mark
 *      @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 {
        union {
                struct {
                        /* These two members must be first. */
                        struct sk_buff          *next;
                        struct sk_buff          *prev;

                        union {
                                struct net_device       *dev;
                                /* Some protocols might use this space to store information,
                                 * while device pointer would be NULL.
                                 * UDP receive path is one user.
                                 */
                                unsigned long           dev_scratch;
                        };
                };
                struct rb_node          rbnode; /* used in netem, ip4 defrag, and tcp stack */
                struct list_head        list;
        };

        union {
                struct sock             *sk;
                int                     ip_defrag_offset;
        };

        union {
                ktime_t         tstamp;
                u64             skb_mstamp_ns; /* earliest departure time */
        };
        /*
         * 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);

        union {
                struct {
                        unsigned long   _skb_refdst;
                        void            (*destructor)(struct sk_buff *skb);
                };
                struct list_head        tcp_tsorted_anchor;
        };

#ifdef CONFIG_XFRM
        struct  sec_path        *sp;
#endif
#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
        unsigned long            _nfct;
#endif
#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
        struct nf_bridge_info   *nf_bridge;
#endif
        unsigned int            len,
                                data_len;
        __u16                   mac_len,
                                hdr_len;

        /* Following fields are _not_ copied in __copy_skb_header()
         * Note that queue_mapping is here mostly to fill a hole.
         */
        __u16                   queue_mapping;

/* if you move cloned around you also must adapt those constants */
#ifdef __BIG_ENDIAN_BITFIELD
#define CLONED_MASK     (1 << 7)
#else
#define CLONED_MASK     1
#endif
#define CLONED_OFFSET()         offsetof(struct sk_buff, __cloned_offset)

        __u8                    __cloned_offset[0];
        __u8                    cloned:1,
                                nohdr:1,
                                fclone:2,
                                peeked:1,
                                head_frag:1,
                                xmit_more:1,
                                pfmemalloc:1;

        /* fields enclosed in headers_start/headers_end are copied
         * using a single memcpy() in __copy_skb_header()
         */
        /* private: */
        __u32                   headers_start[0];
        /* public: */

/* if you move pkt_type around you also must adapt those constants */
#ifdef __BIG_ENDIAN_BITFIELD
#define PKT_TYPE_MAX    (7 << 5)
#else
#define PKT_TYPE_MAX    7
#endif
#define PKT_TYPE_OFFSET()       offsetof(struct sk_buff, __pkt_type_offset)

        __u8                    __pkt_type_offset[0];
        __u8                    pkt_type:3;
        __u8                    ignore_df:1;
        __u8                    nf_trace:1;
        __u8                    ip_summed:2;
        __u8                    ooo_okay:1;

        __u8                    l4_hash:1;
        __u8                    sw_hash:1;
        __u8                    wifi_acked_valid:1;
        __u8                    wifi_acked:1;
        __u8                    no_fcs:1;
        /* Indicates the inner headers are valid in the skbuff. */
        __u8                    encapsulation:1;
        __u8                    encap_hdr_csum:1;
        __u8                    csum_valid:1;

        __u8                    csum_complete_sw:1;
        __u8                    csum_level:2;
        __u8                    csum_not_inet:1;
        __u8                    dst_pending_confirm:1;
#ifdef CONFIG_IPV6_NDISC_NODETYPE
        __u8                    ndisc_nodetype:2;
#endif
        __u8                    ipvs_property:1;

        __u8                    inner_protocol_type:1;
        __u8                    remcsum_offload:1;
#ifdef CONFIG_NET_SWITCHDEV
        __u8                    offload_fwd_mark:1;
        __u8                    offload_mr_fwd_mark:1;
#endif
#ifdef CONFIG_NET_CLS_ACT
        __u8                    tc_skip_classify:1;
        __u8                    tc_at_ingress:1;
        __u8                    tc_redirected:1;
        __u8                    tc_from_ingress:1;
#endif
#ifdef CONFIG_TLS_DEVICE
        __u8                    decrypted:1;
#endif

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

        union {
                __wsum          csum;
                struct {
                        __u16   csum_start;
                        __u16   csum_offset;
                };
        };
        __u32                   priority;
        int                     skb_iif;
        __u32                   hash;
        __be16                  vlan_proto;
        __u16                   vlan_tci;
#if defined(CONFIG_NET_RX_BUSY_POLL) || defined(CONFIG_XPS)
        union {
                unsigned int    napi_id;
                unsigned int    sender_cpu;
        };
#endif
#ifdef CONFIG_NETWORK_SECMARK
        __u32           secmark;
#endif

        union {
                __u32           mark;
                __u32           reserved_tailroom;
        };

        union {
                __be16          inner_protocol;
                __u8            inner_ipproto;
        };

        __u16                   inner_transport_header;
        __u16                   inner_network_header;
        __u16                   inner_mac_header;

        __be16                  protocol;
        __u16                   transport_header;
        __u16                   network_header;
        __u16                   mac_header;

        /* private: */
        __u32                   headers_end[0];
        /* public: */

        /* 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;
        refcount_t              users;
};

#ifdef __KERNEL__
/*
 *      Handling routines are only of interest to the kernel
 */

#define SKB_ALLOC_FCLONE        0x01
#define SKB_ALLOC_RX            0x02
#define SKB_ALLOC_NAPI          0x04

/* 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)

#define SKB_NFCT_PTRMASK        ~(7UL)
/**
 * 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;
}

/**
 * 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)
{
        WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
        skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF;
}

/**
 * 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);
}

/* For mangling skb->pkt_type from user space side from applications
 * such as nft, tc, etc, we only allow a conservative subset of
 * possible pkt_types to be set.
*/
static inline bool skb_pkt_type_ok(u32 ptype)
{
        return ptype <= PACKET_OTHERHOST;
}

static inline unsigned int skb_napi_id(const struct sk_buff *skb)
{
#ifdef CONFIG_NET_RX_BUSY_POLL
        return skb->napi_id;
#else
        return 0;
#endif
}

/* decrement the reference count and return true if we can free the skb */
static inline bool skb_unref(struct sk_buff *skb)
{
        if (unlikely(!skb))
                return false;
        if (likely(refcount_read(&skb->users) == 1))
                smp_rmb();
        else if (likely(!refcount_dec_and_test(&skb->users)))
                return false;

        return true;
}

void skb_release_head_state(struct sk_buff *skb);
void kfree_skb(struct sk_buff *skb);
void kfree_skb_list(struct sk_buff *segs);
void skb_tx_error(struct sk_buff *skb);
void consume_skb(struct sk_buff *skb);
void __consume_stateless_skb(struct sk_buff *skb);
void  __kfree_skb(struct sk_buff *skb);
extern struct kmem_cache *skbuff_head_cache;

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

struct sk_buff *__alloc_skb(unsigned int size, gfp_t priority, int flags,
                            int node);
struct sk_buff *__build_skb(void *data, unsigned int frag_size);
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);
}

struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
                                     unsigned long data_len,
                                     int max_page_order,
                                     int *errcode,
                                     gfp_t gfp_mask);

/* Layout of fast clones : [skb1][skb2][fclone_ref] */
struct sk_buff_fclones {
        struct sk_buff  skb1;

        struct sk_buff  skb2;

        refcount_t      fclone_ref;
};

/**
 *      skb_fclone_busy - check if fclone is busy
 *      @sk: socket
 *      @skb: buffer
 *
 * Returns true if skb is a fast clone, and its clone is not freed.
 * Some drivers call skb_orphan() in their ndo_start_xmit(),
 * so we also check that this didnt happen.
 */
static inline bool skb_fclone_busy(const struct sock *sk,
                                   const struct sk_buff *skb)
{
        const struct sk_buff_fclones *fclones;

        fclones = container_of(skb, struct sk_buff_fclones, skb1);

        return skb->fclone == SKB_FCLONE_ORIG &&
               refcount_read(&fclones->fclone_ref) > 1 &&
               fclones->skb2.sk == sk;
}

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);
}

struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src);
void skb_headers_offset_update(struct sk_buff *skb, int off);
int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask);
struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t priority);
void skb_copy_header(struct sk_buff *new, const struct sk_buff *old);
struct sk_buff *skb_copy(const struct sk_buff *skb, gfp_t priority);
struct sk_buff *__pskb_copy_fclone(struct sk_buff *skb, int headroom,
                                   gfp_t gfp_mask, bool fclone);
static inline struct sk_buff *__pskb_copy(struct sk_buff *skb, int headroom,
                                          gfp_t gfp_mask)
{
        return __pskb_copy_fclone(skb, headroom, gfp_mask, false);
}

int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, gfp_t gfp_mask);
struct sk_buff *skb_realloc_headroom(struct sk_buff *skb,
                                     unsigned int headroom);
struct sk_buff *skb_copy_expand(const struct sk_buff *skb, int newheadroom,
                                int newtailroom, gfp_t priority);
int __must_check skb_to_sgvec_nomark(struct sk_buff *skb, struct scatterlist *sg,
                                     int offset, int len);
int __must_check skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg,
                              int offset, int len);
int skb_cow_data(struct sk_buff *skb, int tailbits, struct sk_buff **trailer);
int __skb_pad(struct sk_buff *skb, int pad, bool free_on_error);

/**
 *      skb_pad                 -       zero pad the tail of an skb
 *      @skb: buffer to pad
 *      @pad: space to pad
 *
 *      Ensure that a buffer is followed by a padding area that is zero
 *      filled. Used by network drivers which may DMA or transfer data
 *      beyond the buffer end onto the wire.
 *
 *      May return error in out of memory cases. The skb is freed on error.
 */
static inline int skb_pad(struct sk_buff *skb, int pad)
{
        return __skb_pad(skb, pad, true);
}
#define dev_kfree_skb(a)        consume_skb(a)

int skb_append_pagefrags(struct sk_buff *skb, struct page *page,
                         int offset, size_t size);

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;
};

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

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

/*
 * Packet hash types specify the type of hash in skb_set_hash.
 *
 * Hash types refer to the protocol layer addresses which are used to
 * construct a packet's hash. The hashes are used to differentiate or identify
 * flows of the protocol layer for the hash type. Hash types are either
 * layer-2 (L2), layer-3 (L3), or layer-4 (L4).
 *
 * Properties of hashes:
 *
 * 1) Two packets in different flows have different hash values
 * 2) Two packets in the same flow should have the same hash value
 *
 * A hash at a higher layer is considered to be more specific. A driver should
 * set the most specific hash possible.
 *
 * A driver cannot indicate a more specific hash than the layer at which a hash
 * was computed. For instance an L3 hash cannot be set as an L4 hash.
 *
 * A driver may indicate a hash level which is less specific than the
 * actual layer the hash was computed on. For instance, a hash computed
 * at L4 may be considered an L3 hash. This should only be done if the
 * driver can't unambiguously determine that the HW computed the hash at
 * the higher layer. Note that the "should" in the second property above
 * permits this.
 */
enum pkt_hash_types {
        PKT_HASH_TYPE_NONE,     /* Undefined type */
        PKT_HASH_TYPE_L2,       /* Input: src_MAC, dest_MAC */
        PKT_HASH_TYPE_L3,       /* Input: src_IP, dst_IP */
        PKT_HASH_TYPE_L4,       /* Input: src_IP, dst_IP, src_port, dst_port */
};

static inline void skb_clear_hash(struct sk_buff *skb)
{
        skb->hash = 0;
        skb->sw_hash = 0;
        skb->l4_hash = 0;
}

static inline void skb_clear_hash_if_not_l4(struct sk_buff *skb)
{
        if (!skb->l4_hash)
                skb_clear_hash(skb);
}

static inline void
__skb_set_hash(struct sk_buff *skb, __u32 hash, bool is_sw, bool is_l4)
{
        skb->l4_hash = is_l4;
        skb->sw_hash = is_sw;
        skb->hash = hash;
}

static inline void
skb_set_hash(struct sk_buff *skb, __u32 hash, enum pkt_hash_types type)
{
        /* Used by drivers to set hash from HW */
        __skb_set_hash(skb, hash, false, type == PKT_HASH_TYPE_L4);
}

static inline void
__skb_set_sw_hash(struct sk_buff *skb, __u32 hash, bool is_l4)
{
        __skb_set_hash(skb, hash, true, is_l4);
}

void __skb_get_hash(struct sk_buff *skb);
u32 __skb_get_hash_symmetric(const struct sk_buff *skb);
u32 skb_get_poff(const struct sk_buff *skb);
u32 __skb_get_poff(const struct sk_buff *skb, void *data,
                   const struct flow_keys_basic *keys, int hlen);
__be32 __skb_flow_get_ports(const struct sk_buff *skb, int thoff, u8 ip_proto,
                            void *data, int hlen_proto);

static inline __be32 skb_flow_get_ports(const struct sk_buff *skb,
                                        int thoff, u8 ip_proto)
{
        return __skb_flow_get_ports(skb, thoff, ip_proto, NULL, 0);
}

void skb_flow_dissector_init(struct flow_dissector *flow_dissector,
                             const struct flow_dissector_key *key,
                             unsigned int key_count);

#ifdef CONFIG_NET
int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
                                       struct bpf_prog *prog);

int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr);
#else
static inline int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
                                                     struct bpf_prog *prog)
{
        return -EOPNOTSUPP;
}

static inline int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr)
{
        return -EOPNOTSUPP;
}
#endif

bool __skb_flow_dissect(const struct sk_buff *skb,
                        struct flow_dissector *flow_dissector,
                        void *target_container,
                        void *data, __be16 proto, int nhoff, int hlen,
                        unsigned int flags);

static inline bool skb_flow_dissect(const struct sk_buff *skb,
                                    struct flow_dissector *flow_dissector,
                                    void *target_container, unsigned int flags)
{
        return __skb_flow_dissect(skb, flow_dissector, target_container,
                                  NULL, 0, 0, 0, flags);
}

static inline bool skb_flow_dissect_flow_keys(const struct sk_buff *skb,
                                              struct flow_keys *flow,
                                              unsigned int flags)
{
        memset(flow, 0, sizeof(*flow));
        return __skb_flow_dissect(skb, &flow_keys_dissector, flow,
                                  NULL, 0, 0, 0, flags);
}

static inline bool
skb_flow_dissect_flow_keys_basic(const struct sk_buff *skb,
                                 struct flow_keys_basic *flow, void *data,
                                 __be16 proto, int nhoff, int hlen,
                                 unsigned int flags)
{
        memset(flow, 0, sizeof(*flow));
        return __skb_flow_dissect(skb, &flow_keys_basic_dissector, flow,
                                  data, proto, nhoff, hlen, flags);
}

void
skb_flow_dissect_tunnel_info(const struct sk_buff *skb,
                             struct flow_dissector *flow_dissector,
                             void *target_container);

static inline __u32 skb_get_hash(struct sk_buff *skb)
{
        if (!skb->l4_hash && !skb->sw_hash)
                __skb_get_hash(skb);

        return skb->hash;
}

static inline __u32 skb_get_hash_flowi6(struct sk_buff *skb, const struct flowi6 *fl6)
{
        if (!skb->l4_hash && !skb->sw_hash) {
                struct flow_keys keys;
                __u32 hash = __get_hash_from_flowi6(fl6, &keys);

                __skb_set_sw_hash(skb, hash, flow_keys_have_l4(&keys));
        }

        return skb->hash;
}

__u32 skb_get_hash_perturb(const struct sk_buff *skb, u32 perturb);

static inline __u32 skb_get_hash_raw(const struct sk_buff *skb)
{
        return skb->hash;
}

static inline void skb_copy_hash(struct sk_buff *to, const struct sk_buff *from)
{
        to->hash = from->hash;
        to->sw_hash = from->sw_hash;
        to->l4_hash = from->l4_hash;
};

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

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

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

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

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

static inline struct ubuf_info *skb_zcopy(struct sk_buff *skb)
{
        bool is_zcopy = skb && skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY;

        return is_zcopy ? skb_uarg(skb) : NULL;
}

static inline void skb_zcopy_set(struct sk_buff *skb, struct ubuf_info *uarg)
{
        if (skb && uarg && !skb_zcopy(skb)) {
                sock_zerocopy_get(uarg);
                skb_shinfo(skb)->destructor_arg = uarg;
                skb_shinfo(skb)->tx_flags |= SKBTX_ZEROCOPY_FRAG;
        }
}

/* Release a reference on a zerocopy structure */
static inline void skb_zcopy_clear(struct sk_buff *skb, bool zerocopy)
{
        struct ubuf_info *uarg = skb_zcopy(skb);

        if (uarg) {
                if (uarg->callback == sock_zerocopy_callback) {
                        uarg->zerocopy = uarg->zerocopy && zerocopy;
                        sock_zerocopy_put(uarg);
                } else {
                        uarg->callback(uarg, zerocopy);
                }

                skb_shinfo(skb)->tx_flags &= ~SKBTX_ZEROCOPY_FRAG;
        }
}

/* Abort a zerocopy operation and revert zckey on error in send syscall */
static inline void skb_zcopy_abort(struct sk_buff *skb)
{
        struct ubuf_info *uarg = skb_zcopy(skb);

        if (uarg) {
                sock_zerocopy_put_abort(uarg);
                skb_shinfo(skb)->tx_flags &= ~SKBTX_ZEROCOPY_FRAG;
        }
}

static inline void skb_mark_not_on_list(struct sk_buff *skb)
{
        skb->next = NULL;
}

static inline void skb_list_del_init(struct sk_buff *skb)
{
        __list_del_entry(&skb->list);
        skb_mark_not_on_list(skb);
}

/**
 *      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 == (const 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 == (const 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 == (const 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)
{
        refcount_inc(&skb->users);
        return skb;
}

/*
 * If users == 1, we are the only owner and can avoid redundant atomic changes.
 */

/**
 *      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(gfpflags_allow_blocking(pri));

        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;
}

static inline int skb_header_unclone(struct sk_buff *skb, gfp_t pri)
{
        might_sleep_if(gfpflags_allow_blocking(pri));

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

        return 0;
}

/**
 *      __skb_header_release - release reference to header
 *      @skb: buffer to operate on
 */
static inline void __skb_header_release(struct sk_buff *skb)
{
        skb->nohdr = 1;
        atomic_set(&skb_shinfo(skb)->dataref, 1 + (1 << SKB_DATAREF_SHIFT));
}


/**
 *      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 refcount_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(gfpflags_allow_blocking(pri));
        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(gfpflags_allow_blocking(pri));
        if (skb_cloned(skb)) {
                struct sk_buff *nskb = skb_copy(skb, pri);

                /* Free our shared copy */
                if (likely(nskb))
                        consume_skb(skb);
                else
                        kfree_skb(skb);
                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 - peek at the head of a non-empty &sk_buff_head
 *      @list_: list to peek at
 *
 *      Like skb_peek(), but the caller knows that the list is not empty.
 */
static inline struct sk_buff *__skb_peek(const struct sk_buff_head *list_)
{
        return list_->next;
}

/**
 *      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.
 */
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);
}

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.
 */
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.
 */
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..
 */
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.
 */
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.
 */
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 unsigned int __skb_pagelen(const struct sk_buff *skb)
{
        unsigned int i, len = 0;

        for (i = skb_shinfo(skb)->nr_frags - 1; (int)i >= 0; i--)
                len += skb_frag_size(&skb_shinfo(skb)->frags[i]);
        return len;
}

static inline unsigned int skb_pagelen(const struct sk_buff *skb)
{
        return skb_headlen(skb) + __skb_pagelen(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 but rely
         * on page_is_pfmemalloc doing the right thing(tm).
         */
        frag->page.p              = page;
        frag->page_offset         = off;
        skb_frag_size_set(frag, size);

        page = compound_head(page);
        if (page_is_pfmemalloc(page))
                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;
}

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

void skb_coalesce_rx_frag(struct sk_buff *skb, int i, 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
 */
void *pskb_put(struct sk_buff *skb, struct sk_buff *tail, int len);
void *skb_put(struct sk_buff *skb, unsigned int len);
static inline void *__skb_put(struct sk_buff *skb, unsigned int len)
{
        void *tmp = skb_tail_pointer(skb);
        SKB_LINEAR_ASSERT(skb);
        skb->tail += len;
        skb->len  += len;
        return tmp;
}

static inline void *__skb_put_zero(struct sk_buff *skb, unsigned int len)
{
        void *tmp = __skb_put(skb, len);

        memset(tmp, 0, len);
        return tmp;
}

static inline void *__skb_put_data(struct sk_buff *skb, const void *data,
                                   unsigned int len)
{
        void *tmp = __skb_put(skb, len);

        memcpy(tmp, data, len);
        return tmp;
}

static inline void __skb_put_u8(struct sk_buff *skb, u8 val)
{
        *(u8 *)__skb_put(skb, 1) = val;
}

static inline void *skb_put_zero(struct sk_buff *skb, unsigned int len)
{
        void *tmp = skb_put(skb, len);

        memset(tmp, 0, len);

        return tmp;
}

static inline void *skb_put_data(struct sk_buff *skb, const void *data,
                                 unsigned int len)
{
        void *tmp = skb_put(skb, len);

        memcpy(tmp, data, len);

        return tmp;
}

static inline void skb_put_u8(struct sk_buff *skb, u8 val)
{
        *(u8 *)skb_put(skb, 1) = val;
}

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

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

void *__pskb_pull_tail(struct sk_buff *skb, int delta);

static inline void *__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 void *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;
}

void skb_condense(struct sk_buff *skb);

/**
 *      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;
}

/**
 *      skb_tailroom_reserve - adjust reserved_tailroom
 *      @skb: buffer to alter
 *      @mtu: maximum amount of headlen permitted
 *      @needed_tailroom: minimum amount of reserved_tailroom
 *
 *      Set reserved_tailroom so that headlen can be as large as possible but
 *      not larger than mtu and tailroom cannot be smaller than
 *      needed_tailroom.
 *      The required headroom should already have been reserved before using
 *      this function.
 */
static inline void skb_tailroom_reserve(struct sk_buff *skb, unsigned int mtu,
                                        unsigned int needed_tailroom)
{
        SKB_LINEAR_ASSERT(skb);
        if (mtu < skb_tailroom(skb) - needed_tailroom)
                /* use at most mtu */
                skb->reserved_tailroom = skb_tailroom(skb) - mtu;
        else
                /* use up to all available space */
                skb->reserved_tailroom = needed_tailroom;
}

#define ENCAP_TYPE_ETHER        0
#define ENCAP_TYPE_IPPROTO      1

static inline void skb_set_inner_protocol(struct sk_buff *skb,
                                          __be16 protocol)
{
        skb->inner_protocol = protocol;
        skb->inner_protocol_type = ENCAP_TYPE_ETHER;
}

static inline void skb_set_inner_ipproto(struct sk_buff *skb,
                                         __u8 ipproto)
{
        skb->inner_ipproto = ipproto;
        skb->inner_protocol_type = ENCAP_TYPE_IPPROTO;
}

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 int skb_inner_transport_offset(const struct sk_buff *skb)
{
        return skb_inner_transport_header(skb) - skb->data;
}

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_offset(const struct sk_buff *skb)
{
        return skb_mac_header(skb) - skb->data;
}

static inline u32 skb_mac_header_len(const struct sk_buff *skb)
{
        return skb->network_header - 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_pop_mac_header(struct sk_buff *skb)
{
        skb->mac_header = skb->network_header;
}

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

        if (skb_transport_header_was_set(skb))
                return;

        if (skb_flow_dissect_flow_keys_basic(skb, &keys, NULL, 0, 0, 0, 0))
                skb_set_transport_header(skb, keys.control.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 unsigned char *skb_checksum_start(const struct sk_buff *skb)
{
        return skb->head + skb->csum_start;
}

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

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

static inline void __skb_set_length(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);
}

static inline void __skb_trim(struct sk_buff *skb, unsigned int len)
{
        __skb_set_length(skb, len);
}

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);
}

static inline int __skb_grow(struct sk_buff *skb, unsigned int len)
{
        unsigned int diff = len - skb->len;

        if (skb_tailroom(skb) < diff) {
                int ret = pskb_expand_head(skb, 0, diff - skb_tailroom(skb),
                                           GFP_ATOMIC);
                if (ret)
                        return ret;
        }
        __skb_set_length(skb, len);
        return 0;
}

/**
 *      skb_orphan - orphan a buffer
 *      @skb: buffer to orphan
 *
 *      If a buffer currently has an owner then we call the owner's
 *      destructor function and make the @skb unowned. The buffer continues
 *      to exist but is no longer charged to its former owner.
 */
static inline void skb_orphan(struct sk_buff *skb)
{
        if (skb->destructor) {
                skb->destructor(skb);
                skb->destructor = NULL;
                skb->sk         = NULL;
        } 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_zcopy(skb)))
                return 0;
        if (skb_uarg(skb)->callback == sock_zerocopy_callback)
                return 0;
        return skb_copy_ubufs(skb, gfp_mask);
}

/* Frags must be orphaned, even if refcounted, if skb might loop to rx path */
static inline int skb_orphan_frags_rx(struct sk_buff *skb, gfp_t gfp_mask)
{
        if (likely(!skb_zcopy(skb)))
                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.
 */
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);
}

unsigned int skb_rbtree_purge(struct rb_root *root);

void *netdev_alloc_frag(unsigned int fragsz);

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);
}

static inline void skb_free_frag(void *addr)
{
        page_frag_free(addr);
}

void *napi_alloc_frag(unsigned int fragsz);
struct sk_buff *__napi_alloc_skb(struct napi_struct *napi,
                                 unsigned int length, gfp_t gfp_mask);
static inline struct sk_buff *napi_alloc_skb(struct napi_struct *napi,
                                             unsigned int length)
{
        return __napi_alloc_skb(napi, length, GFP_ATOMIC);
}
void napi_consume_skb(struct sk_buff *skb, int budget);

void __kfree_skb_flush(void);
void __kfree_skb_defer(struct sk_buff *skb);

/**
 * __dev_alloc_pages - allocate page for network Rx
 * @gfp_mask: allocation priority. Set __GFP_NOMEMALLOC if not for network Rx
 * @order: size of the allocation
 *
 * Allocate a new page.
 *
 * %NULL is returned if there is no free memory.
*/
static inline struct page *__dev_alloc_pages(gfp_t gfp_mask,
                                             unsigned int order)
{
        /* This piece of code contains several assumptions.
         * 1.  This is for device Rx, therefor a cold page is preferred.
         * 2.  The expectation is the user wants a compound page.
         * 3.  If requesting a order 0 page it will not be compound
         *     due to the check to see if order has a value in prep_new_page
         * 4.  __GFP_MEMALLOC is ignored if __GFP_NOMEMALLOC is set due to
         *     code in gfp_to_alloc_flags that should be enforcing this.
         */
        gfp_mask |= __GFP_COMP | __GFP_MEMALLOC;

        return alloc_pages_node(NUMA_NO_NODE, gfp_mask, order);
}

static inline struct page *dev_alloc_pages(unsigned int order)
{
        return __dev_alloc_pages(GFP_ATOMIC | __GFP_NOWARN, order);
}

/**
 * __dev_alloc_page - allocate a page for network Rx
 * @gfp_mask: allocation priority. Set __GFP_NOMEMALLOC if not for network Rx
 *
 * Allocate a new page.
 *
 * %NULL is returned if there is no free memory.
 */
static inline struct page *__dev_alloc_page(gfp_t gfp_mask)
{
        return __dev_alloc_pages(gfp_mask, 0);
}

static inline struct page *dev_alloc_page(void)
{
        return dev_alloc_pages(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_is_pfmemalloc(page))
                skb->pfmemalloc = true;
}

/**
 * skb_frag_page - retrieve the page referred 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);
}

bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t prio);

/**
 * 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);
}


static inline struct sk_buff *pskb_copy_for_clone(struct sk_buff *skb,
                                                  gfp_t gfp_mask)
{
        return __pskb_copy_fclone(skb, skb_headroom(skb), gfp_mask, true);
}


/**
 *      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_try_make_writable(struct sk_buff *skb,
                                        unsigned int write_len)
{
        return skb_cloned(skb) && !skb_clone_writable(skb, write_len) &&
               pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
}

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);
}

/**
 *      skb_put_padto - increase size and pad an skbuff up to a minimal size
 *      @skb: buffer to pad
 *      @len: minimal length
 *      @free_on_error: free buffer on error
 *
 *      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 if @free_on_error is true.
 */
static inline int __skb_put_padto(struct sk_buff *skb, unsigned int len,
                                  bool free_on_error)
{
        unsigned int size = skb->len;

        if (unlikely(size < len)) {
                len -= size;
                if (__skb_pad(skb, len, free_on_error))
                        return -ENOMEM;
                __skb_put(skb, len);
        }
        return 0;
}

/**
 *      skb_put_padto - increase size and 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_put_padto(struct sk_buff *skb, unsigned int len)
{
        return __skb_put_padto(skb, len, true);
}

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

        if (skb->ip_summed == CHECKSUM_NONE) {
                __wsum csum = 0;
                if (csum_and_copy_from_iter_full(skb_put(skb, copy), copy,
                                                 &csum, from)) {
                        skb->csum = csum_block_add(skb->csum, csum, off);
                        return 0;
                }
        } else if (copy_from_iter_full(skb_put(skb, copy), copy, from))
                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 (skb_zcopy(skb))
                return false;
        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;
}

static __always_inline void
__skb_postpull_rcsum(struct sk_buff *skb, const void *start, unsigned int len,
                     unsigned int off)
{
        if (skb->ip_summed == CHECKSUM_COMPLETE)
                skb->csum = csum_block_sub(skb->csum,
                                           csum_partial(start, len, 0), off);
        else if (skb->ip_summed == CHECKSUM_PARTIAL &&
                 skb_checksum_start_offset(skb) < 0)
                skb->ip_summed = CHECKSUM_NONE;
}

/**
 *      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)
{
        __skb_postpull_rcsum(skb, start, len, 0);
}

static __always_inline void
__skb_postpush_rcsum(struct sk_buff *skb, const void *start, unsigned int len,
                     unsigned int off)
{
        if (skb->ip_summed == CHECKSUM_COMPLETE)
                skb->csum = csum_block_add(skb->csum,
                                           csum_partial(start, len, 0), off);
}

/**
 *      skb_postpush_rcsum - update checksum for received skb after push
 *      @skb: buffer to update
 *      @start: start of data after push
 *      @len: length of data pushed
 *
 *      After doing a push on a received packet, you need to call this to
 *      update the CHECKSUM_COMPLETE checksum.
 */
static inline void skb_postpush_rcsum(struct sk_buff *skb,
                                      const void *start, unsigned int len)
{
        __skb_postpush_rcsum(skb, start, len, 0);
}

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

/**
 *      skb_push_rcsum - push skb and update receive checksum
 *      @skb: buffer to update
 *      @len: length of data pulled
 *
 *      This function performs an skb_push on the packet and updates
 *      the CHECKSUM_COMPLETE checksum.  It should be used on
 *      receive path processing instead of skb_push unless you know
 *      that the checksum difference is zero (e.g., a valid IP header)
 *      or you are setting ip_summed to CHECKSUM_NONE.
 */
static inline void *skb_push_rcsum(struct sk_buff *skb, unsigned int len)
{
        skb_push(skb, len);
        skb_postpush_rcsum(skb, skb->data, len);
        return skb->data;
}

int pskb_trim_rcsum_slow(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;
        return pskb_trim_rcsum_slow(skb, len);
}

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

static inline int __skb_grow_rcsum(struct sk_buff *skb, unsigned int len)
{
        if (skb->ip_summed == CHECKSUM_COMPLETE)
                skb->ip_summed = CHECKSUM_NONE;
        return __skb_grow(skb, len);
}

#define rb_to_skb(rb) rb_entry_safe(rb, struct sk_buff, rbnode)
#define skb_rb_first(root) rb_to_skb(rb_first(root))
#define skb_rb_last(root)  rb_to_skb(rb_last(root))
#define skb_rb_next(skb)   rb_to_skb(rb_next(&(skb)->rbnode))
#define skb_rb_prev(skb)   rb_to_skb(rb_prev(&(skb)->rbnode))

#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_rbtree_walk(skb, root)                                              \
                for (skb = skb_rb_first(root); skb != NULL;                     \
                     skb = skb_rb_next(skb))

#define skb_rbtree_walk_from(skb)                                               \
                for (; skb != NULL;                                             \
                     skb = skb_rb_next(skb))

#define skb_rbtree_walk_from_safe(skb, tmp)                                     \
                for (; tmp = skb ? skb_rb_next(skb) : NULL, (skb != NULL);      \
                     skb = tmp)

#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;
}

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


int __skb_wait_for_more_packets(struct sock *sk, int *err, long *timeo_p,
                                const struct sk_buff *skb);
struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,
                                          struct sk_buff_head *queue,
                                          unsigned int flags,
                                          void (*destructor)(struct sock *sk,
                                                           struct sk_buff *skb),
                                          int *peeked, int *off, int *err,
                                          struct sk_buff **last);
struct sk_buff *__skb_try_recv_datagram(struct sock *sk, unsigned flags,
                                        void (*destructor)(struct sock *sk,
                                                           struct sk_buff *skb),
                                        int *peeked, int *off, int *err,
                                        struct sk_buff **last);
struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned flags,
                                    void (*destructor)(struct sock *sk,
                                                       struct sk_buff *skb),
                                    int *peeked, int *off, int *err);
struct sk_buff *skb_recv_datagram(struct sock *sk, unsigned flags, int noblock,
                                  int *err);
__poll_t datagram_poll(struct file *file, struct socket *sock,
                           struct poll_table_struct *wait);
int skb_copy_datagram_iter(const struct sk_buff *from, int offset,
                           struct iov_iter *to, int size);
static inline int skb_copy_datagram_msg(const struct sk_buff *from, int offset,
                                        struct msghdr *msg, int size)
{
        return skb_copy_datagram_iter(from, offset, &msg->msg_iter, size);
}
int skb_copy_and_csum_datagram_msg(struct sk_buff *skb, int hlen,
                                   struct msghdr *msg);
int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
                                 struct iov_iter *from, int len);
int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *frm);
void skb_free_datagram(struct sock *sk, struct sk_buff *skb);
void __skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb, int len);
static inline void skb_free_datagram_locked(struct sock *sk,
                                            struct sk_buff *skb)
{
        __skb_free_datagram_locked(sk, skb, 0);
}
int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags);
int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len);
int skb_store_bits(struct sk_buff *skb, int offset, const void *from, int len);
__wsum skb_copy_and_csum_bits(const struct sk_buff *skb, int offset, u8 *to,
                              int len, __wsum csum);
int skb_splice_bits(struct sk_buff *skb, struct sock *sk, unsigned int offset,
                    struct pipe_inode_info *pipe, unsigned int len,
                    unsigned int flags);
int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
                         int len);
int skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset, int len);
void skb_copy_and_csum_dev(const struct sk_buff *skb, u8 *to);
unsigned int skb_zerocopy_headlen(const struct sk_buff *from);
int skb_zerocopy(struct sk_buff *to, struct sk_buff *from,
                 int len, int hlen);
void skb_split(struct sk_buff *skb, struct sk_buff *skb1, const u32 len);
int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen);
void skb_scrub_packet(struct sk_buff *skb, bool xnet);
bool skb_gso_validate_network_len(const struct sk_buff *skb, unsigned int mtu);
bool skb_gso_validate_mac_len(const struct sk_buff *skb, unsigned int len);
struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features);
struct sk_buff *skb_vlan_untag(struct sk_buff *skb);
int skb_ensure_writable(struct sk_buff *skb, int write_len);
int __skb_vlan_pop(struct sk_buff *skb, u16 *vlan_tci);
int skb_vlan_pop(struct sk_buff *skb);
int skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci);
struct sk_buff *pskb_extract(struct sk_buff *skb, int off, int to_copy,
                             gfp_t gfp);

static inline int memcpy_from_msg(void *data, struct msghdr *msg, int len)
{
        return copy_from_iter_full(data, len, &msg->msg_iter) ? 0 : -EFAULT;
}

static inline int memcpy_to_msg(struct msghdr *msg, void *data, int len)
{
        return copy_to_iter(data, len, &msg->msg_iter) == len ? 0 : -EFAULT;
}

struct skb_checksum_ops {
        __wsum (*update)(const void *mem, int len, __wsum wsum);
        __wsum (*combine)(__wsum csum, __wsum csum2, int offset, int len);
};

extern const struct skb_checksum_ops *crc32c_csum_stub __read_mostly;

__wsum __skb_checksum(const struct sk_buff *skb, int offset, int len,
                      __wsum csum, const struct skb_checksum_ops *ops);
__wsum skb_checksum(const struct sk_buff *skb, int offset, int len,
                    __wsum csum);

static inline void * __must_check
__skb_header_pointer(const struct sk_buff *skb, int offset,
                     int len, void *data, int hlen, void *buffer)
{
        if (hlen - offset >= len)
                return data + offset;

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

        return buffer;
}

static inline void * __must_check
skb_header_pointer(const struct sk_buff *skb, int offset, int len, void *buffer)
{
        return __skb_header_pointer(skb, offset, len, skb->data,
                                    skb_headlen(skb), buffer);
}

/**
 *      skb_needs_linearize - check if we need to linearize a given skb
 *                            depending on the given device features.
 *      @skb: socket buffer to check
 *      @features: net device features
 *
 *      Returns true if either:
 *      1. skb has frag_list and the device doesn't support FRAGLIST, or
 *      2. skb is fragmented and the device does not support SG.
 */
static inline bool skb_needs_linearize(struct sk_buff *skb,
                                       netdev_features_t features)
{
        return skb_is_nonlinear(skb) &&
               ((skb_has_frag_list(skb) && !(features & NETIF_F_FRAGLIST)) ||
                (skb_shinfo(skb)->nr_frags && !(features & NETIF_F_SG)));
}

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);
}

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 0;
}

static inline u8 skb_metadata_len(const struct sk_buff *skb)
{
        return skb_shinfo(skb)->meta_len;
}

static inline void *skb_metadata_end(const struct sk_buff *skb)
{
        return skb_mac_header(skb);
}

static inline bool __skb_metadata_differs(const struct sk_buff *skb_a,
                                          const struct sk_buff *skb_b,
                                          u8 meta_len)
{
        const void *a = skb_metadata_end(skb_a);
        const void *b = skb_metadata_end(skb_b);
        /* Using more efficient varaiant than plain call to memcmp(). */
#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && BITS_PER_LONG == 64
        u64 diffs = 0;

        switch (meta_len) {
#define __it(x, op) (x -= sizeof(u##op))
#define __it_diff(a, b, op) (*(u##op *)__it(a, op)) ^ (*(u##op *)__it(b, op))
        case 32: diffs |= __it_diff(a, b, 64);
                 /* fall through */
        case 24: diffs |= __it_diff(a, b, 64);
                 /* fall through */
        case 16: diffs |= __it_diff(a, b, 64);
                 /* fall through */
        case  8: diffs |= __it_diff(a, b, 64);
                break;
        case 28: diffs |= __it_diff(a, b, 64);
                 /* fall through */
        case 20: diffs |= __it_diff(a, b, 64);
                 /* fall through */
        case 12: diffs |= __it_diff(a, b, 64);
                 /* fall through */
        case  4: diffs |= __it_diff(a, b, 32);
                break;
        }
        return diffs;
#else
        return memcmp(a - meta_len, b - meta_len, meta_len);
#endif
}

static inline bool skb_metadata_differs(const struct sk_buff *skb_a,
                                        const struct sk_buff *skb_b)
{
        u8 len_a = skb_metadata_len(skb_a);
        u8 len_b = skb_metadata_len(skb_b);

        if (!(len_a | len_b))
                return false;

        return len_a != len_b ?
               true : __skb_metadata_differs(skb_a, skb_b, len_a);
}

static inline void skb_metadata_set(struct sk_buff *skb, u8 meta_len)
{
        skb_shinfo(skb)->meta_len = meta_len;
}

static inline void skb_metadata_clear(struct sk_buff *skb)
{
        skb_metadata_set(skb, 0);
}

struct sk_buff *skb_clone_sk(struct sk_buff *skb);

#ifdef CONFIG_NETWORK_PHY_TIMESTAMPING

void skb_clone_tx_timestamp(struct sk_buff *skb);
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 a
 * timestamp.
 *
 * @skb: clone of the the original outgoing packet
 * @hwtstamps: hardware time stamps
 *
 */
void skb_complete_tx_timestamp(struct sk_buff *skb,
                               struct skb_shared_hwtstamps *hwtstamps);

void __skb_tstamp_tx(struct sk_buff *orig_skb,
                     struct skb_shared_hwtstamps *hwtstamps,
                     struct sock *sk, int tstype);

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

/**
 * 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.
 *
 * Specifically, one should make absolutely sure that this function is
 * called before TX completion of this packet can trigger.  Otherwise
 * the packet could potentially already be freed.
 *
 * @skb: A socket buffer.
 */
static inline void skb_tx_timestamp(struct sk_buff *skb)
{
        skb_clone_tx_timestamp(skb);
        if (skb_shinfo(skb)->tx_flags & SKBTX_SW_TSTAMP)
                skb_tstamp_tx(skb, NULL);
}

/**
 * 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);

__sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len);
__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->csum_valid ||
                (skb->ip_summed == CHECKSUM_PARTIAL &&
                 skb_checksum_start_offset(skb) >= 0));
}

/**
 *      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);
}

static inline void __skb_decr_checksum_unnecessary(struct sk_buff *skb)
{
        if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
                if (skb->csum_level == 0)
                        skb->ip_summed = CHECKSUM_NONE;
                else
                        skb->csum_level--;
        }
}

static inline void __skb_incr_checksum_unnecessary(struct sk_buff *skb)
{
        if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
                if (skb->csum_level < SKB_MAX_CSUM_LEVEL)
                        skb->csum_level++;
        } else if (skb->ip_summed == CHECKSUM_NONE) {
                skb->ip_summed = CHECKSUM_UNNECESSARY;
                skb->csum_level = 0;
        }
}

/* Check if we need to perform checksum complete validation.
 *
 * Returns true if checksum complete is needed, false otherwise
 * (either checksum is unnecessary or zero checksum is allowed).
 */
static inline bool __skb_checksum_validate_needed(struct sk_buff *skb,
                                                  bool zero_okay,
                                                  __sum16 check)
{
        if (skb_csum_unnecessary(skb) || (zero_okay && !check)) {
                skb->csum_valid = 1;
                __skb_decr_checksum_unnecessary(skb);
                return false;
        }

        return true;
}

/* For small packets <= CHECKSUM_BREAK perform checksum complete directly
 * in checksum_init.
 */
#define CHECKSUM_BREAK 76

/* Unset checksum-complete
 *
 * Unset checksum complete can be done when packet is being modified
 * (uncompressed for instance) and checksum-complete value is
 * invalidated.
 */
static inline void skb_checksum_complete_unset(struct sk_buff *skb)
{
        if (skb->ip_summed == CHECKSUM_COMPLETE)
                skb->ip_summed = CHECKSUM_NONE;
}

/* Validate (init) checksum based on checksum complete.
 *
 * Return values:
 *   0: checksum is validated or try to in skb_checksum_complete. In the latter
 *      case the ip_summed will not be CHECKSUM_UNNECESSARY and the pseudo
 *      checksum is stored in skb->csum for use in __skb_checksum_complete
 *   non-zero: value of invalid checksum
 *
 */
static inline __sum16 __skb_checksum_validate_complete(struct sk_buff *skb,
                                                       bool complete,
                                                       __wsum psum)
{
        if (skb->ip_summed == CHECKSUM_COMPLETE) {
                if (!csum_fold(csum_add(psum, skb->csum))) {
                        skb->csum_valid = 1;
                        return 0;
                }
        }

        skb->csum = psum;

        if (complete || skb->len <= CHECKSUM_BREAK) {
                __sum16 csum;

                csum = __skb_checksum_complete(skb);
                skb->csum_valid = !csum;
                return csum;
        }

        return 0;
}

static inline __wsum null_compute_pseudo(struct sk_buff *skb, int proto)
{
        return 0;
}

/* Perform checksum validate (init). Note that this is a macro since we only
 * want to calculate the pseudo header which is an input function if necessary.
 * First we try to validate without any computation (checksum unnecessary) and
 * then calculate based on checksum complete calling the function to compute
 * pseudo header.
 *
 * Return values:
 *   0: checksum is validated or try to in skb_checksum_complete
 *   non-zero: value of invalid checksum
 */
#define __skb_checksum_validate(skb, proto, complete,                   \
                                zero_okay, check, compute_pseudo)       \
({                                                                      \
        __sum16 __ret = 0;                                              \
        skb->csum_valid = 0;                                            \
        if (__skb_checksum_validate_needed(skb, zero_okay, check))      \
                __ret = __skb_checksum_validate_complete(skb,           \
                                complete, compute_pseudo(skb, proto));  \
        __ret;                                                          \
})

#define skb_checksum_init(skb, proto, compute_pseudo)                   \
        __skb_checksum_validate(skb, proto, false, false, 0, compute_pseudo)

#define skb_checksum_init_zero_check(skb, proto, check, compute_pseudo) \
        __skb_checksum_validate(skb, proto, false, true, check, compute_pseudo)

#define skb_checksum_validate(skb, proto, compute_pseudo)               \
        __skb_checksum_validate(skb, proto, true, false, 0, compute_pseudo)

#define skb_checksum_validate_zero_check(skb, proto, check,             \
                                         compute_pseudo)                \
        __skb_checksum_validate(skb, proto, true, true, check, compute_pseudo)

#define skb_checksum_simple_validate(skb)                               \
        __skb_checksum_validate(skb, 0, true, false, 0, null_compute_pseudo)

static inline bool __skb_checksum_convert_check(struct sk_buff *skb)
{
        return (skb->ip_summed == CHECKSUM_NONE && skb->csum_valid);
}

static inline void __skb_checksum_convert(struct sk_buff *skb,
                                          __sum16 check, __wsum pseudo)
{
        skb->csum = ~pseudo;
        skb->ip_summed = CHECKSUM_COMPLETE;
}

#define skb_checksum_try_convert(skb, proto, check, compute_pseudo)     \
do {                                                                    \
        if (__skb_checksum_convert_check(skb))                          \
                __skb_checksum_convert(skb, check,                      \
                                       compute_pseudo(skb, proto));     \
} while (0)

static inline void skb_remcsum_adjust_partial(struct sk_buff *skb, void *ptr,
                                              u16 start, u16 offset)
{
        skb->ip_summed = CHECKSUM_PARTIAL;
        skb->csum_start = ((unsigned char *)ptr + start) - skb->head;
        skb->csum_offset = offset - start;
}

/* Update skbuf and packet to reflect the remote checksum offload operation.
 * When called, ptr indicates the starting point for skb->csum when
 * ip_summed is CHECKSUM_COMPLETE. If we need create checksum complete
 * here, skb_postpull_rcsum is done so skb->csum start is ptr.
 */
static inline void skb_remcsum_process(struct sk_buff *skb, void *ptr,
                                       int start, int offset, bool nopartial)
{
        __wsum delta;

        if (!nopartial) {
                skb_remcsum_adjust_partial(skb, ptr, start, offset);
                return;
        }

         if (unlikely(skb->ip_summed != CHECKSUM_COMPLETE)) {
                __skb_checksum_complete(skb);
                skb_postpull_rcsum(skb, skb->data, ptr - (void *)skb->data);
        }

        delta = remcsum_adjust(ptr, skb->csum, start, offset);

        /* Adjust skb->csum since we changed the packet */
        skb->csum = csum_add(skb->csum, delta);
}

static inline struct nf_conntrack *skb_nfct(const struct sk_buff *skb)
{
#if IS_ENABLED(CONFIG_NF_CONNTRACK)
        return (void *)(skb->_nfct & SKB_NFCT_PTRMASK);
#else
        return NULL;
#endif
}

#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
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
#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
static inline void nf_bridge_put(struct nf_bridge_info *nf_bridge)
{
        if (nf_bridge && refcount_dec_and_test(&nf_bridge->use))
                kfree(nf_bridge);
}
static inline void nf_bridge_get(struct nf_bridge_info *nf_bridge)
{
        if (nf_bridge)
                refcount_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));
        skb->_nfct = 0;
#endif
#if IS_ENABLED(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) || defined(CONFIG_NF_TABLES)
        skb->nf_trace = 0;
#endif
}

static inline void ipvs_reset(struct sk_buff *skb)
{
#if IS_ENABLED(CONFIG_IP_VS)
        skb->ipvs_property = 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,
                             bool copy)
{
#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
        dst->_nfct = src->_nfct;
        nf_conntrack_get(skb_nfct(src));
#endif
#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
        dst->nf_bridge  = src->nf_bridge;
        nf_bridge_get(src->nf_bridge);
#endif
#if IS_ENABLED(CONFIG_NETFILTER_XT_TARGET_TRACE) || defined(CONFIG_NF_TABLES)
        if (copy)
                dst->nf_trace = src->nf_trace;
#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(skb_nfct(dst));
#endif
#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
        nf_bridge_put(dst->nf_bridge);
#endif
        __nf_copy(dst, src, true);
}

#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 bool skb_irq_freeable(const struct sk_buff *skb)
{
        return !skb->destructor &&
#if IS_ENABLED(CONFIG_XFRM)
                !skb->sp &&
#endif
                !skb_nfct(skb) &&
                !skb->_skb_refdst &&
                !skb_has_frag_list(skb);
}

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;
}

static inline void skb_set_dst_pending_confirm(struct sk_buff *skb, u32 val)
{
        skb->dst_pending_confirm = val;
}

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

static inline struct sec_path *skb_sec_path(struct sk_buff *skb)
{
#ifdef CONFIG_XFRM
        return skb->sp;
#else
        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.
 * Keeps track of level of encapsulation of network headers.
 */
struct skb_gso_cb {
        union {
                int     mac_offset;
                int     data_offset;
        };
        int     encap_level;
        __wsum  csum;
        __u16   csum_start;
};
#define SKB_SGO_CB_OFFSET       32
#define SKB_GSO_CB(skb) ((struct skb_gso_cb *)((skb)->cb + SKB_SGO_CB_OFFSET))

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 void gso_reset_checksum(struct sk_buff *skb, __wsum res)
{
        /* Do not update partial checksums if remote checksum is enabled. */
        if (skb->remcsum_offload)
                return;

        SKB_GSO_CB(skb)->csum = res;
        SKB_GSO_CB(skb)->csum_start = skb_checksum_start(skb) - skb->head;
}

/* Compute the checksum for a gso segment. First compute the checksum value
 * from the start of transport header to SKB_GSO_CB(skb)->csum_start, and
 * then add in skb->csum (checksum from csum_start to end of packet).
 * skb->csum and csum_start are then updated to reflect the checksum of the
 * resultant packet starting from the transport header-- the resultant checksum
 * is in the res argument (i.e. normally zero or ~ of checksum of a pseudo
 * header.
 */
static inline __sum16 gso_make_checksum(struct sk_buff *skb, __wsum res)
{
        unsigned char *csum_start = skb_transport_header(skb);
        int plen = (skb->head + SKB_GSO_CB(skb)->csum_start) - csum_start;
        __wsum partial = SKB_GSO_CB(skb)->csum;

        SKB_GSO_CB(skb)->csum = res;
        SKB_GSO_CB(skb)->csum_start = csum_start - skb->head;

        return csum_fold(csum_partial(csum_start, plen, partial));
}

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

/* Note: Should be called only if skb_is_gso(skb) is true */
static inline bool skb_is_gso_v6(const struct sk_buff *skb)
{
        return skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6;
}

/* Note: Should be called only if skb_is_gso(skb) is true */
static inline bool skb_is_gso_sctp(const struct sk_buff *skb)
{
        return skb_shinfo(skb)->gso_type & SKB_GSO_SCTP;
}

static inline void skb_gso_reset(struct sk_buff *skb)
{
        skb_shinfo(skb)->gso_size = 0;
        skb_shinfo(skb)->gso_segs = 0;
        skb_shinfo(skb)->gso_type = 0;
}

static inline void skb_increase_gso_size(struct skb_shared_info *shinfo,
                                         u16 increment)
{
        if (WARN_ON_ONCE(shinfo->gso_size == GSO_BY_FRAGS))
                return;
        shinfo->gso_size += increment;
}

static inline void skb_decrease_gso_size(struct skb_shared_info *shinfo,
                                         u16 decrement)
{
        if (WARN_ON_ONCE(shinfo->gso_size == GSO_BY_FRAGS))
                return;
        shinfo->gso_size -= decrement;
}

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);

int skb_checksum_setup(struct sk_buff *skb, bool recalculate);
struct sk_buff *skb_checksum_trimmed(struct sk_buff *skb,
                                     unsigned int transport_len,
                                     __sum16(*skb_chkf)(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);
}

/* Local Checksum Offload.
 * Compute outer checksum based on the assumption that the
 * inner checksum will be offloaded later.
 * See Documentation/networking/checksum-offloads.txt for
 * explanation of how this works.
 * Fill in outer checksum adjustment (e.g. with sum of outer
 * pseudo-header) before calling.
 * Also ensure that inner checksum is in linear data area.
 */
static inline __wsum lco_csum(struct sk_buff *skb)
{
        unsigned char *csum_start = skb_checksum_start(skb);
        unsigned char *l4_hdr = skb_transport_header(skb);
        __wsum partial;

        /* Start with complement of inner checksum adjustment */
        partial = ~csum_unfold(*(__force __sum16 *)(csum_start +
                                                    skb->csum_offset));

        /* Add in checksum of our headers (incl. outer checksum
         * adjustment filled in by caller) and return result.
         */
        return csum_partial(l4_hdr, csum_start - l4_hdr, partial);
}

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