TOMOYO Linux Cross Reference
Linux/include/linux/skbuff.h

   /*
    *      Definitions for the 'struct sk_buff' memory handlers.
    *
    *      Authors:
    *              Alan Cox, <gw4pts@gw4pts.ampr.org>
    *              Florian La Roche, <rzsfl@rz.uni-sb.de>
    *
    *      This program is free software; you can redistribute it and/or
    *      modify it under the terms of the GNU General Public License
   *      as published by the Free Software Foundation; either version
   *      2 of the License, or (at your option) any later version.
   */
  
  #ifndef _LINUX_SKBUFF_H
  #define _LINUX_SKBUFF_H
  
  #include <linux/kernel.h>
  #include <linux/kmemcheck.h>
  #include <linux/compiler.h>
  #include <linux/time.h>
  #include <linux/bug.h>
  #include <linux/cache.h>
  #include <linux/rbtree.h>
  #include <linux/socket.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 <net/flow_dissector.h>
  #include <linux/splice.h>
  #include <linux/in6.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.
  *
  *   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.
  *
  *   Note: Even if device supports only some protocols, but is able to produce
  *   skb->csum, it MUST use CHECKSUM_COMPLETE, not CHECKSUM_UNNECESSARY.
  *
  * 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. If a  device has limited checksum capabilities
  *   (for instance can only perform NETIF_F_IP_CSUM or NETIF_F_IPV6_CSUM as
  *   described above) a helper function can be called to resolve
  *   CHECKSUM_PARTIAL. The helper functions are skb_csum_off_chk*. The helper
  *   function takes a spec argument that describes the protocol layer that is
  *   supported for checksum offload and can be called for each packet. If a
  *   packet does not match the specification for offload, skb_checksum_help
  *   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 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 SCTP checksum, a driver that supports
  *     both IP checksum offload and SCTP CRC offload must verify which offload
  *     is configured for a packet presumably by inspecting packet headers.
  *
  *   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;
 
 #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 {
         atomic_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;
 
 typedef struct skb_frag_struct skb_frag_t;
 
 struct skb_frag_struct {
         struct {
                 struct page *p;
         } page;
 #if (BITS_PER_LONG > 32) || (PAGE_SIZE >= 65536)
         __u32 page_offset;
         __u32 size;
 #else
         __u16 page_offset;
         __u16 size;
 #endif
 };
 
 static inline unsigned int skb_frag_size(const skb_frag_t *frag)
 {
         return frag->size;
 }
 
 static inline void skb_frag_size_set(skb_frag_t *frag, unsigned int size)
 {
         frag->size = size;
 }
 
 static inline void skb_frag_size_add(skb_frag_t *frag, int delta)
 {
         frag->size += delta;
 }
 
 static inline void skb_frag_size_sub(skb_frag_t *frag, int delta)
 {
         frag->size -= delta;
 }
 
 #define HAVE_HW_TIME_STAMP
 
 /**
  * struct skb_shared_hwtstamps - hardware time stamps
  * @hwtstamp:   hardware time stamp transformed into duration
  *              since arbitrary point in time
  *
  * 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_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);
         void *ctx;
         unsigned long desc;
 };
 
 /* This data is invariant across clones and lives at
  * the end of the header data, ie. at skb->end.
  */
 struct skb_shared_info {
         unsigned char   nr_frags;
         __u8            tx_flags;
         unsigned short  gso_size;
         /* Warning: this field is not always filled in (UFO)! */
         unsigned short  gso_segs;
         unsigned short  gso_type;
         struct sk_buff  *frag_list;
         struct skb_shared_hwtstamps hwtstamps;
         u32             tskey;
         __be32          ip6_frag_id;
 
         /*
          * Warning : all fields before dataref are cleared in __alloc_skb()
          */
         atomic_t        dataref;
 
         /* Intermediate layers must ensure that destructor_arg
          * remains valid until skb destructor */
         void *          destructor_arg;
 
         /* must be last field, see pskb_expand_head() */
         skb_frag_t      frags[MAX_SKB_FRAGS];
 };
 
 /* We divide dataref into two halves.  The higher 16 bits hold references
  * to the payload part of skb->data.  The lower 16 bits hold references to
  * the entire skb->data.  A clone of a headerless skb holds the length of
  * the header in skb->hdr_len.
  *
  * All users must obey the rule that the skb->data reference count must be
  * greater than or equal to the payload reference count.
  *
  * Holding a reference to the payload part means that the user does not
  * care about modifications to the header part of skb->data.
  */
 #define SKB_DATAREF_SHIFT 16
 #define SKB_DATAREF_MASK ((1 << SKB_DATAREF_SHIFT) - 1)
 
 
 enum {
         SKB_FCLONE_UNAVAILABLE, /* skb 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,
         SKB_GSO_UDP = 1 << 1,
 
         /* This indicates the skb is from an untrusted source. */
         SKB_GSO_DODGY = 1 << 2,
 
         /* This indicates the tcp segment has CWR set. */
         SKB_GSO_TCP_ECN = 1 << 3,
 
         SKB_GSO_TCP_FIXEDID = 1 << 4,
 
         SKB_GSO_TCPV6 = 1 << 5,
 
         SKB_GSO_FCOE = 1 << 6,
 
         SKB_GSO_GRE = 1 << 7,
 
         SKB_GSO_GRE_CSUM = 1 << 8,
 
         SKB_GSO_IPXIP4 = 1 << 9,
 
         SKB_GSO_IPXIP6 = 1 << 10,
 
         SKB_GSO_UDP_TUNNEL = 1 << 11,
 
         SKB_GSO_UDP_TUNNEL_CSUM = 1 << 12,
 
         SKB_GSO_PARTIAL = 1 << 13,
 
         SKB_GSO_TUNNEL_REMCSUM = 1 << 14,
 };
 
 #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 skb_mstamp - multi resolution time stamps
  * @stamp_us: timestamp in us resolution
  * @stamp_jiffies: timestamp in jiffies
  */
 struct skb_mstamp {
         union {
                 u64             v64;
                 struct {
                         u32     stamp_us;
                         u32     stamp_jiffies;
                 };
         };
 };
 
 /**
  * skb_mstamp_get - get current timestamp
  * @cl: place to store timestamps
  */
 static inline void skb_mstamp_get(struct skb_mstamp *cl)
 {
         u64 val = local_clock();
 
         do_div(val, NSEC_PER_USEC);
         cl->stamp_us = (u32)val;
         cl->stamp_jiffies = (u32)jiffies;
 }
 
 /**
  * skb_mstamp_delta - compute the difference in usec between two skb_mstamp
  * @t1: pointer to newest sample
  * @t0: pointer to oldest sample
  */
 static inline u32 skb_mstamp_us_delta(const struct skb_mstamp *t1,
                                       const struct skb_mstamp *t0)
 {
         s32 delta_us = t1->stamp_us - t0->stamp_us;
         u32 delta_jiffies = t1->stamp_jiffies - t0->stamp_jiffies;
 
         /* If delta_us is negative, this might be because interval is too big,
          * or local_clock() drift is too big : fallback using jiffies.
          */
         if (delta_us <= 0 ||
             delta_jiffies >= (INT_MAX / (USEC_PER_SEC / HZ)))
 
                 delta_us = jiffies_to_usecs(delta_jiffies);
 
         return delta_us;
 }
 
 static inline bool skb_mstamp_after(const struct skb_mstamp *t1,
                                     const struct skb_mstamp *t0)
 {
         s32 diff = t1->stamp_jiffies - t0->stamp_jiffies;
 
         if (!diff)
                 diff = t1->stamp_us - t0->stamp_us;
         return diff > 0;
 }
 
 /** 
  *      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
  *      @nfctinfo: Relationship of this skb to the connection
  *      @pkt_type: Packet class
  *      @fclone: skbuff clone status
  *      @ipvs_property: skbuff is owned by ipvs
  *      @peeked: this packet has been seen already, so stats have been
  *              done for it, don't do them again
  *      @nf_trace: netfilter packet trace flag
  *      @protocol: Packet protocol from driver
  *      @destructor: Destruct function
  *      @nfct: Associated connection, if any
  *      @nf_bridge: Saved data about a bridged frame - see br_netfilter.c
  *      @skb_iif: ifindex of device we arrived on
  *      @tc_index: Traffic control index
  *      @tc_verd: traffic control verdict
  *      @hash: the packet hash
  *      @queue_mapping: Queue mapping for multiqueue devices
  *      @xmit_more: More SKBs are pending for this queue
  *      @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
   *     @napi_id: id of the NAPI struct this skb came from
  *      @secmark: security marking
  *      @offload_fwd_mark: fwding offload mark
  *      @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 {
                                 ktime_t         tstamp;
                                 struct skb_mstamp skb_mstamp;
                         };
                 };
                 struct rb_node  rbnode; /* used in netem & tcp stack */
         };
         struct sock             *sk;
         struct net_device       *dev;
 
         /*
          * This is the control buffer. It is free to use for every
          * layer. Please put your private variables there. If you
          * want to keep them across layers you have to do a skb_clone()
          * first. This is owned by whoever has the skb queued ATM.
          */
         char                    cb[48] __aligned(8);
 
         unsigned long           _skb_refdst;
         void                    (*destructor)(struct sk_buff *skb);
 #ifdef CONFIG_XFRM
         struct  sec_path        *sp;
 #endif
 #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
         struct nf_conntrack     *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.
          */
         kmemcheck_bitfield_begin(flags1);
         __u16                   queue_mapping;
         __u8                    cloned:1,
                                 nohdr:1,
                                 fclone:2,
                                 peeked:1,
                                 head_frag:1,
                                 xmit_more:1;
         /* one bit hole */
         kmemcheck_bitfield_end(flags1);
 
         /* 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                    pfmemalloc:1;
         __u8                    ignore_df:1;
         __u8                    nfctinfo:3;
 
         __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_bad:1;
 
 #ifdef CONFIG_IPV6_NDISC_NODETYPE
         __u8                    ndisc_nodetype:2;
 #endif
         __u8                    ipvs_property:1;
         __u8                    inner_protocol_type:1;
         __u8                    remcsum_offload:1;
         /* 3 or 5 bit hole */
 
 #ifdef CONFIG_NET_SCHED
         __u16                   tc_index;       /* traffic control index */
 #ifdef CONFIG_NET_CLS_ACT
         __u16                   tc_verd;        /* traffic control verdict */
 #endif
 #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
         union {
 #ifdef CONFIG_NETWORK_SECMARK
                 __u32           secmark;
 #endif
 #ifdef CONFIG_NET_SWITCHDEV
                 __u32           offload_fwd_mark;
 #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;
         atomic_t                users;
 };
 
 #ifdef __KERNEL__
 /*
  *      Handling routines are only of interest to the kernel
  */
 #include <linux/slab.h>
 
 
 #define SKB_ALLOC_FCLONE        0x01
 #define SKB_ALLOC_RX            0x02
 #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)
 
 /**
  * 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);
 }
 
 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  __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;
 
         atomic_t        fclone_ref;
 };
 
 /**
  *      skb_fclone_busy - check if fclone is busy
  *      @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 &&
                atomic_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 *__alloc_skb_head(gfp_t priority, int node);
 static inline struct sk_buff *alloc_skb_head(gfp_t priority)
 {
         return __alloc_skb_head(priority, -1);
 }
 
 struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src);
 int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask);
 struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t priority);
 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 skb_to_sgvec_nomark(struct sk_buff *skb, struct scatterlist *sg,
                         int offset, int len);
 int 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);
 #define dev_kfree_skb(a)        consume_skb(a)
 
 int skb_append_datato_frags(struct sock *sk, struct sk_buff *skb,
                             int getfrag(void *from, char *to, int offset,
                                         int len, int odd, struct sk_buff *skb),
                             void *from, int length);
 
 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(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 *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);
 
 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_buf(struct flow_keys *flow,
                                                   void *data, __be16 proto,
                                                   int nhoff, int hlen,
                                                   unsigned int flags)
 {
         memset(flow, 0, sizeof(*flow));
         return __skb_flow_dissect(NULL, &flow_keys_buf_dissector, flow,
                                   data, proto, nhoff, hlen, flags);
 }
 
 static inline __u32 skb_get_hash(struct sk_buff *skb)
 {
         if (!skb->l4_hash && !skb->sw_hash)
                 __skb_get_hash(skb);
 
         return skb->hash;
 }
 
 __u32 __skb_get_hash_flowi6(struct sk_buff *skb, const struct flowi6 *fl6);
 
 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_flowi4(struct sk_buff *skb, const struct flowi4 *fl);
 
 static inline __u32 skb_get_hash_flowi4(struct sk_buff *skb, const struct flowi4 *fl4)
 {
         if (!skb->l4_hash && !skb->sw_hash) {
                 struct flow_keys keys;
                 __u32 hash = __get_hash_from_flowi4(fl4, &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;
 }
 
 /**
  *      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)
 {
         atomic_inc(&skb->users);
         return skb;
 }
 
 /*
  * If users == 1, we are the only owner and are can avoid redundant
  * atomic change.
  */
 
 /**
  *      skb_cloned - is the buffer a clone
  *      @skb: buffer to check
  *
  *      Returns true if the buffer was generated with skb_clone() and is
  *      one of multiple shared copies of the buffer. Cloned buffers are
  *      shared data so must not be written to under normal circumstances.
  */
 static inline int skb_cloned(const struct sk_buff *skb)
 {
         return skb->cloned &&
                (atomic_read(&skb_shinfo(skb)->dataref) & SKB_DATAREF_MASK) != 1;
 }
 
 static inline int skb_unclone(struct sk_buff *skb, gfp_t pri)
 {
         might_sleep_if(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
  *
  *      Drop a reference to the header part of the buffer.  This is done
  *      by acquiring a payload reference.  You must not read from the header
  *      part of skb->data after this.
  *      Note : Check if you can use __skb_header_release() instead.
  */
 static inline void skb_header_release(struct sk_buff *skb)
 {
         BUG_ON(skb->nohdr);
         skb->nohdr = 1;
         atomic_add(1 << SKB_DATAREF_SHIFT, &skb_shinfo(skb)->dataref);
 }
 
 /**
  *      __skb_header_release - release reference to header
  *      @skb: buffer to operate on
  *
  *      Variant of skb_header_release() assuming skb is private to caller.
  *      We can avoid one atomic operation.
  */
 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 atomic_read(&skb->users) != 1;
 }
 
 /**
  *      skb_share_check - check if buffer is shared and if so clone it
  *      @skb: buffer to check
  *      @pri: priority for memory allocation
  *
  *      If the buffer is shared the buffer is cloned and the old copy
  *      drops a reference. A new clone with a single reference is returned.
  *      If the buffer is not shared the original buffer is returned. When
  *      being called from interrupt status or with spinlocks held pri must
  *      be GFP_ATOMIC.
  *
  *      NULL is returned on a memory allocation failure.
  */
 static inline struct sk_buff *skb_share_check(struct sk_buff *skb, gfp_t pri)
 {
         might_sleep_if(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_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 int skb_pagelen(const struct sk_buff *skb)
 {
         int i, len = 0;
 
         for (i = (int)skb_shinfo(skb)->nr_frags - 1; i >= 0; i--)
                 len += skb_frag_size(&skb_shinfo(skb)->frags[i]);
         return len + skb_headlen(skb);
 }
 
 /**
  * __skb_fill_page_desc - initialise a paged fragment in an skb
  * @skb: buffer containing fragment to be initialised
  * @i: paged fragment index to initialise
  * @page: the page to use for this fragment
  * @off: the offset to the data with @page
  * @size: the length of the data
  *
  * Initialises the @i'th fragment of @skb to point to &size bytes at
  * offset @off within @page.
  *
  * Does not take any additional reference on the fragment.
  */
 static inline void __skb_fill_page_desc(struct sk_buff *skb, int i,
                                         struct page *page, int off, int size)
 {
         skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 
         /*
          * Propagate page pfmemalloc to the skb if we can. The problem is
          * that not all callers have unique ownership of the page 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
  */
 unsigned char *pskb_put(struct sk_buff *skb, struct sk_buff *tail, int len);
 unsigned char *skb_put(struct sk_buff *skb, unsigned int len);
 static inline unsigned char *__skb_put(struct sk_buff *skb, unsigned int len)
 {
         unsigned char *tmp = skb_tail_pointer(skb);
         SKB_LINEAR_ASSERT(skb);
         skb->tail += len;
         skb->len  += len;
         return tmp;
 }
 
 unsigned char *skb_push(struct sk_buff *skb, unsigned int len);
 static inline unsigned char *__skb_push(struct sk_buff *skb, unsigned int len)
 {
         skb->data -= len;
         skb->len  += len;
         return skb->data;
 }
 
 unsigned char *skb_pull(struct sk_buff *skb, unsigned int len);
 static inline unsigned char *__skb_pull(struct sk_buff *skb, unsigned int len)
 {
         skb->len -= len;
         BUG_ON(skb->len < skb->data_len);
         return skb->data += len;
 }
 
 static inline unsigned char *skb_pull_inline(struct sk_buff *skb, unsigned int len)
 {
         return unlikely(len > skb->len) ? NULL : __skb_pull(skb, len);
 }
 
 unsigned char *__pskb_pull_tail(struct sk_buff *skb, int delta);
 
 static inline unsigned char *__pskb_pull(struct sk_buff *skb, unsigned int len)
 {
         if (len > skb_headlen(skb) &&
             !__pskb_pull_tail(skb, len - skb_headlen(skb)))
                 return NULL;
         skb->len -= len;
         return skb->data += len;
 }
 
 static inline unsigned char *pskb_pull(struct sk_buff *skb, unsigned int len)
 {
         return unlikely(len > skb->len) ? NULL : __pskb_pull(skb, len);
 }
 
 static inline int pskb_may_pull(struct sk_buff *skb, unsigned int len)
 {
         if (likely(len <= skb_headlen(skb)))
                 return 1;
         if (unlikely(len > skb->len))
                 return 0;
         return __pskb_pull_tail(skb, len - skb_headlen(skb)) != NULL;
 }
 
 /**
  *      skb_headroom - bytes at buffer head
  *      @skb: buffer to check
  *
  *      Return the number of bytes of free space at the head of an &sk_buff.
  */
 static inline unsigned int skb_headroom(const struct sk_buff *skb)
 {
         return skb->data - skb->head;
 }
 
 /**
  *      skb_tailroom - bytes at buffer end
  *      @skb: buffer to check
  *
  *      Return the number of bytes of free space at the tail of an sk_buff
  */
 static inline int skb_tailroom(const struct sk_buff *skb)
 {
         return skb_is_nonlinear(skb) ? 0 : skb->end - skb->tail;
 }
 
 /**
  *      skb_availroom - bytes at buffer end
  *      @skb: buffer to check
  *
  *      Return the number of bytes of free space at the tail of an sk_buff
  *      allocated by sk_stream_alloc()
  */
 static inline int skb_availroom(const struct sk_buff *skb)
 {
         if (skb_is_nonlinear(skb))
                 return 0;
 
         return skb->end - skb->tail - skb->reserved_tailroom;
 }
 
 /**
  *      skb_reserve - adjust headroom
  *      @skb: buffer to alter
  *      @len: bytes to move
  *
  *      Increase the headroom of an empty &sk_buff by reducing the tail
  *      room. This is only allowed for an empty buffer.
  */
 static inline void skb_reserve(struct sk_buff *skb, int len)
 {
         skb->data += len;
         skb->tail += len;
 }
 
 /**
  *      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_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 keys;
 
         if (skb_transport_header_was_set(skb))
                 return;
         else if (skb_flow_dissect_flow_keys(skb, &keys, 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_trim(struct sk_buff *skb, unsigned int len)
 {
         if (unlikely(skb_is_nonlinear(skb))) {
                 WARN_ON(1);
                 return;
         }
         skb->len = len;
         skb_set_tail_pointer(skb, len);
 }
 
 void skb_trim(struct sk_buff *skb, unsigned int len);
 
 static inline int __pskb_trim(struct sk_buff *skb, unsigned int len)
 {
         if (skb->data_len)
                 return ___pskb_trim(skb, len);
         __skb_trim(skb, len);
         return 0;
 }
 
 static inline int pskb_trim(struct sk_buff *skb, unsigned int len)
 {
         return (len < skb->len) ? __pskb_trim(skb, len) : 0;
 }
 
 /**
  *      pskb_trim_unique - remove end from a paged unique (not cloned) buffer
  *      @skb: buffer to alter
  *      @len: new length
  *
  *      This is identical to pskb_trim except that the caller knows that
  *      the skb is not cloned so we should never get an error due to out-
  *      of-memory.
  */
 static inline void pskb_trim_unique(struct sk_buff *skb, unsigned int len)
 {
         int err = pskb_trim(skb, len);
         BUG_ON(err);
 }
 
 /**
  *      skb_orphan - orphan a buffer
  *      @skb: buffer to orphan
  *
  *      If a buffer currently has an owner then we call the owner's
  *      destructor function and make the @skb unowned. The buffer continues
  *      to exist but is no longer charged to its former owner.
  */
 static inline void skb_orphan(struct sk_buff *skb)
 {
         if (skb->destructor) {
                 skb->destructor(skb);
                 skb->destructor = NULL;
                 skb->sk         = NULL;
         } else {
                 BUG_ON(skb->sk);
         }
 }
 
 /**
  *      skb_orphan_frags - orphan the frags contained in a buffer
  *      @skb: buffer to orphan frags from
  *      @gfp_mask: allocation mask for replacement pages
  *
  *      For each frag in the SKB which needs a destructor (i.e. has an
  *      owner) create a copy of that frag and release the original
  *      page by calling the destructor.
  */
 static inline int skb_orphan_frags(struct sk_buff *skb, gfp_t gfp_mask)
 {
         if (likely(!(skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY)))
                 return 0;
         return skb_copy_ubufs(skb, gfp_mask);
 }
 
 /**
  *      __skb_queue_purge - empty a list
  *      @list: list to empty
  *
  *      Delete all buffers on an &sk_buff list. Each buffer is removed from
  *      the list and one reference dropped. This function does not take the
  *      list lock and the caller must hold the relevant locks to use it.
  */
 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);
 }
 
 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)
 {
         __free_page_frag(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_COLD | __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
  *
  *      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)
 {
         unsigned int size = skb->len;
 
         if (unlikely(size < len)) {
                 len -= size;
                 if (skb_pad(skb, len))
                         return -ENOMEM;
                 __skb_put(skb, len);
         }
         return 0;
 }
 
 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(skb_put(skb, copy), copy,
                                             &csum, from) == copy) {
                         skb->csum = csum_block_add(skb->csum, csum, off);
                         return 0;
                 }
         } else if (copy_from_iter(skb_put(skb, copy), copy, from) == copy)
                 return 0;
 
         __skb_trim(skb, off);
         return -EFAULT;
 }
 
 static inline bool skb_can_coalesce(struct sk_buff *skb, int i,
                                     const struct page *page, int off)
 {
         if (i) {
                 const struct skb_frag_struct *frag = &skb_shinfo(skb)->frags[i - 1];
 
                 return page == skb_frag_page(frag) &&
                        off == frag->page_offset + skb_frag_size(frag);
         }
         return false;
 }
 
 static inline int __skb_linearize(struct sk_buff *skb)
 {
         return __pskb_pull_tail(skb, skb->data_len) ? 0 : -ENOMEM;
 }
 
 /**
  *      skb_linearize - convert paged skb to linear one
  *      @skb: buffer to linarize
  *
  *      If there is no free memory -ENOMEM is returned, otherwise zero
  *      is returned and the old skb data released.
  */
 static inline int skb_linearize(struct sk_buff *skb)
 {
         return skb_is_nonlinear(skb) ? __skb_linearize(skb) : 0;
 }
 
 /**
  * skb_has_shared_frag - can any frag be overwritten
  * @skb: buffer to test
  *
  * Return true if the skb has at least one frag that might be modified
  * by an external entity (as in vmsplice()/sendfile())
  */
 static inline bool skb_has_shared_frag(const struct sk_buff *skb)
 {
         return skb_is_nonlinear(skb) &&
                skb_shinfo(skb)->tx_flags & SKBTX_SHARED_FRAG;
 }
 
 /**
  *      skb_linearize_cow - make sure skb is linear and writable
  *      @skb: buffer to process
  *
  *      If there is no free memory -ENOMEM is returned, otherwise zero
  *      is returned and the old skb data released.
  */
 static inline int skb_linearize_cow(struct sk_buff *skb)
 {
         return skb_is_nonlinear(skb) || skb_cloned(skb) ?
                __skb_linearize(skb) : 0;
 }
 
 /**
  *      skb_postpull_rcsum - update checksum for received skb after pull
  *      @skb: buffer to update
  *      @start: start of data before pull
  *      @len: length of data pulled
  *
  *      After doing a pull on a received packet, you need to call this to
  *      update the CHECKSUM_COMPLETE checksum, or set ip_summed to
  *      CHECKSUM_NONE so that it can be recomputed from scratch.
  */
 
 static inline void skb_postpull_rcsum(struct sk_buff *skb,
                                       const void *start, unsigned int len)
 {
         if (skb->ip_summed == CHECKSUM_COMPLETE)
                 skb->csum = csum_sub(skb->csum, csum_partial(start, len, 0));
         else if (skb->ip_summed == CHECKSUM_PARTIAL &&
                  skb_checksum_start_offset(skb) < 0)
                 skb->ip_summed = CHECKSUM_NONE;
 }
 
 unsigned char *skb_pull_rcsum(struct sk_buff *skb, unsigned int len);
 
 static inline void skb_postpush_rcsum(struct sk_buff *skb,
                                       const void *start, unsigned int len)
 {
         /* For performing the reverse operation to skb_postpull_rcsum(),
          * we can instead of ...
          *
          *   skb->csum = csum_add(skb->csum, csum_partial(start, len, 0));
          *
          * ... just use this equivalent version here to save a few
          * instructions. Feeding csum of 0 in csum_partial() and later
          * on adding skb->csum is equivalent to feed skb->csum in the
          * first place.
          */
         if (skb->ip_summed == CHECKSUM_COMPLETE)
                 skb->csum = csum_partial(start, len, skb->csum);
 }
 
 /**
  *      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 unsigned char *skb_push_rcsum(struct sk_buff *skb,
                                             unsigned int len)
 {
         skb_push(skb, len);
         skb_postpush_rcsum(skb, skb->data, len);
         return skb->data;
 }
 
 /**
  *      pskb_trim_rcsum - trim received skb and update checksum
  *      @skb: buffer to trim
  *      @len: new length
  *
  *      This is exactly the same as pskb_trim except that it ensures the
  *      checksum of received packets are still valid after the operation.
  */
 
 static inline int pskb_trim_rcsum(struct sk_buff *skb, unsigned int len)
 {
         if (likely(len >= skb->len))
                 return 0;
         if (skb->ip_summed == CHECKSUM_COMPLETE)
                 skb->ip_summed = CHECKSUM_NONE;
         return __pskb_trim(skb, len);
 }
 
 #define skb_queue_walk(queue, skb) \
                 for (skb = (queue)->next;                                       \
                      skb != (struct sk_buff *)(queue);                          \
                      skb = skb->next)
 
 #define skb_queue_walk_safe(queue, skb, tmp)                                    \
                 for (skb = (queue)->next, tmp = skb->next;                      \
                      skb != (struct sk_buff *)(queue);                          \
                      skb = tmp, tmp = skb->next)
 
 #define skb_queue_walk_from(queue, skb)                                         \
                 for (; skb != (struct sk_buff *)(queue);                        \
                      skb = skb->next)
 
 #define skb_queue_walk_from_safe(queue, skb, tmp)                               \
                 for (tmp = skb->next;                                           \
                      skb != (struct sk_buff *)(queue);                          \
                      skb = tmp, tmp = skb->next)
 
 #define skb_queue_reverse_walk(queue, skb) \
                 for (skb = (queue)->prev;                                       \
                      skb != (struct sk_buff *)(queue);                          \
                      skb = skb->prev)
 
 #define skb_queue_reverse_walk_safe(queue, skb, tmp)                            \
                 for (skb = (queue)->prev, tmp = skb->prev;                      \
                      skb != (struct sk_buff *)(queue);                          \
                      skb = tmp, tmp = skb->prev)
 
 #define skb_queue_reverse_walk_from_safe(queue, skb, tmp)                       \
                 for (tmp = skb->prev;                                           \
                      skb != (struct sk_buff *)(queue);                          \
                      skb = tmp, tmp = skb->prev)
 
 static inline bool skb_has_frag_list(const struct sk_buff *skb)
 {
         return skb_shinfo(skb)->frag_list != NULL;
 }
 
 static inline void skb_frag_list_init(struct sk_buff *skb)
 {
         skb_shinfo(skb)->frag_list = NULL;
 }
 
 #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_datagram(struct sock *sk, unsigned flags,
                                         int *peeked, int *off, int *err,
                                         struct sk_buff **last);
 struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned flags,
                                     int *peeked, int *off, int *err);
 struct sk_buff *skb_recv_datagram(struct sock *sk, unsigned flags, int noblock,
                                   int *err);
 unsigned int 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);
 ssize_t skb_socket_splice(struct sock *sk,
                           struct pipe_inode_info *pipe,
                           struct splice_pipe_desc *spd);
 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,
                     ssize_t (*splice_cb)(struct sock *,
                                          struct pipe_inode_info *,
                                          struct splice_pipe_desc *));
 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);
 unsigned int skb_gso_transport_seglen(const struct sk_buff *skb);
 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);
 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(data, len, &msg->msg_iter) == len ? 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);
 };
 
 __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 ktime_set(0, 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);
 
 static inline void sw_tx_timestamp(struct sk_buff *skb)
 {
         if (skb_shinfo(skb)->tx_flags & SKBTX_SW_TSTAMP &&
             !(skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS))
                 skb_tstamp_tx(skb, NULL);
 }
 
 /**
  * skb_tx_timestamp() - Driver hook for transmit timestamping
  *
  * Ethernet MAC Drivers should call this function in their hard_xmit()
  * function immediately before giving the sk_buff to the MAC hardware.
  *
  * 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);
         sw_tx_timestamp(skb);
 }
 
 /**
  * skb_complete_wifi_ack - deliver skb with wifi status
  *
  * @skb: the original outgoing packet
  * @acked: ack status
  *
  */
 void skb_complete_wifi_ack(struct sk_buff *skb, bool acked);
 
 __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;
         }
 }
 
 static inline void __skb_mark_checksum_bad(struct sk_buff *skb)
 {
         /* Mark current checksum as bad (typically called from GRO
          * path). In the case that ip_summed is CHECKSUM_NONE
          * this must be the first checksum encountered in the packet.
          * When ip_summed is CHECKSUM_UNNECESSARY, this is the first
          * checksum after the last one validated. For UDP, a zero
          * checksum can not be marked as bad.
          */
 
         if (skb->ip_summed == CHECKSUM_NONE ||
             skb->ip_summed == CHECKSUM_UNNECESSARY)
                 skb->csum_bad = 1;
 }
 
 /* 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 peform 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;
                 }
         } else if (skb->csum_bad) {
                 /* ip_summed == CHECKSUM_NONE in this case */
                 return (__force __sum16)1;
         }
 
         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 && !skb->csum_bad);
 }
 
 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);
 }
 
 #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 && atomic_dec_and_test(&nf_bridge->use))
                 kfree(nf_bridge);
 }
 static inline void nf_bridge_get(struct nf_bridge_info *nf_bridge)
 {
         if (nf_bridge)
                 atomic_inc(&nf_bridge->use);
 }
 #endif /* CONFIG_BRIDGE_NETFILTER */
 static inline void nf_reset(struct sk_buff *skb)
 {
 #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
         nf_conntrack_put(skb->nfct);
         skb->nfct = NULL;
 #endif
 #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
 }
 
 /* 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(src->nfct);
         if (copy)
                 dst->nfctinfo = src->nfctinfo;
 #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(dst->nfct);
 #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
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
                 !skb->nfct &&
 #endif
                 !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 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;
 }
 
 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);
 }
 
 /**
  * skb_gso_network_seglen - Return length of individual segments of a gso packet
  *
  * @skb: GSO skb
  *
  * skb_gso_network_seglen is used to determine the real size of the
  * individual segments, including Layer3 (IP, IPv6) and L4 headers (TCP/UDP).
  *
  * The MAC/L2 header is not accounted for.
  */
 static inline unsigned int skb_gso_network_seglen(const struct sk_buff *skb)
 {
         unsigned int hdr_len = skb_transport_header(skb) -
                                skb_network_header(skb);
         return hdr_len + skb_gso_transport_seglen(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 */