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 #ifndef __NET_NSH_H
 #define __NET_NSH_H 1
 
 #include <linux/skbuff.h>
 
 /*
  * Network Service Header:
  *  0                   1                   2                   3
  *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  * |Ver|O|U|    TTL    |   Length  |U|U|U|U|MD Type| Next Protocol |
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  * |          Service Path Identifier (SPI)        | Service Index |
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  * |                                                               |
  * ~               Mandatory/Optional Context Headers              ~
  * |                                                               |
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  *
  * Version: The version field is used to ensure backward compatibility
  * going forward with future NSH specification updates.  It MUST be set
  * to 0x0 by the sender, in this first revision of NSH.  Given the
  * widespread implementation of existing hardware that uses the first
  * nibble after an MPLS label stack for ECMP decision processing, this
  * document reserves version 01b and this value MUST NOT be used in
  * future versions of the protocol.  Please see [RFC7325] for further
  * discussion of MPLS-related forwarding requirements.
  *
  * O bit: Setting this bit indicates an Operations, Administration, and
  * Maintenance (OAM) packet.  The actual format and processing of SFC
  * OAM packets is outside the scope of this specification (see for
  * example [I-D.ietf-sfc-oam-framework] for one approach).
  *
  * The O bit MUST be set for OAM packets and MUST NOT be set for non-OAM
  * packets.  The O bit MUST NOT be modified along the SFP.
  *
  * SF/SFF/SFC Proxy/Classifier implementations that do not support SFC
  * OAM procedures SHOULD discard packets with O bit set, but MAY support
  * a configurable parameter to enable forwarding received SFC OAM
  * packets unmodified to the next element in the chain.  Forwarding OAM
  * packets unmodified by SFC elements that do not support SFC OAM
  * procedures may be acceptable for a subset of OAM functions, but can
  * result in unexpected outcomes for others, thus it is recommended to
  * analyze the impact of forwarding an OAM packet for all OAM functions
  * prior to enabling this behavior.  The configurable parameter MUST be
  * disabled by default.
  *
  * TTL: Indicates the maximum SFF hops for an SFP.  This field is used
  * for service plane loop detection.  The initial TTL value SHOULD be
  * configurable via the control plane; the configured initial value can
  * be specific to one or more SFPs.  If no initial value is explicitly
  * provided, the default initial TTL value of 63 MUST be used.  Each SFF
  * involved in forwarding an NSH packet MUST decrement the TTL value by
  * 1 prior to NSH forwarding lookup.  Decrementing by 1 from an incoming
  * value of 0 shall result in a TTL value of 63.  The packet MUST NOT be
  * forwarded if TTL is, after decrement, 0.
  *
  * All other flag fields, marked U, are unassigned and available for
  * future use, see Section 11.2.1.  Unassigned bits MUST be set to zero
  * upon origination, and MUST be ignored and preserved unmodified by
  * other NSH supporting elements.  Elements which do not understand the
  * meaning of any of these bits MUST NOT modify their actions based on
  * those unknown bits.
  *
  * Length: The total length, in 4-byte words, of NSH including the Base
  * Header, the Service Path Header, the Fixed Length Context Header or
  * Variable Length Context Header(s).  The length MUST be 0x6 for MD
  * Type equal to 0x1, and MUST be 0x2 or greater for MD Type equal to
  * 0x2.  The length of the NSH header MUST be an integer multiple of 4
  * bytes, thus variable length metadata is always padded out to a
  * multiple of 4 bytes.
  *
  * MD Type: Indicates the format of NSH beyond the mandatory Base Header
  * and the Service Path Header.  MD Type defines the format of the
  * metadata being carried.
  *
  * 0x0 - This is a reserved value.  Implementations SHOULD silently
  * discard packets with MD Type 0x0.
  *
  * 0x1 - This indicates that the format of the header includes a fixed
  * length Context Header (see Figure 4 below).
  *
  * 0x2 - This does not mandate any headers beyond the Base Header and
  * Service Path Header, but may contain optional variable length Context
  * Header(s).  The semantics of the variable length Context Header(s)
  * are not defined in this document.  The format of the optional
  * variable length Context Headers is provided in Section 2.5.1.
  *
  * 0xF - This value is reserved for experimentation and testing, as per
  * [RFC3692].  Implementations not explicitly configured to be part of
  * an experiment SHOULD silently discard packets with MD Type 0xF.
  *
  * Next Protocol: indicates the protocol type of the encapsulated data.
  * NSH does not alter the inner payload, and the semantics on the inner
  * protocol remain unchanged due to NSH service function chaining.
  * Please see the IANA Considerations section below, Section 11.2.5.
  *
  * This document defines the following Next Protocol values:
  *
  * 0x1: IPv4
  * 0x2: IPv6
  * 0x3: Ethernet
  * 0x4: NSH
  * 0x5: MPLS
  * 0xFE: Experiment 1
  * 0xFF: Experiment 2
  *
  * Packets with Next Protocol values not supported SHOULD be silently
  * dropped by default, although an implementation MAY provide a
  * configuration parameter to forward them.  Additionally, an
  * implementation not explicitly configured for a specific experiment
  * [RFC3692] SHOULD silently drop packets with Next Protocol values 0xFE
  * and 0xFF.
  *
  * Service Path Identifier (SPI): Identifies a service path.
  * Participating nodes MUST use this identifier for Service Function
  * Path selection.  The initial classifier MUST set the appropriate SPI
  * for a given classification result.
  *
  * Service Index (SI): Provides location within the SFP.  The initial
  * classifier for a given SFP SHOULD set the SI to 255, however the
  * control plane MAY configure the initial value of SI as appropriate
  * (i.e., taking into account the length of the service function path).
  * The Service Index MUST be decremented by a value of 1 by Service
  * Functions or by SFC Proxy nodes after performing required services
  * and the new decremented SI value MUST be used in the egress packet's
  * NSH.  The initial Classifier MUST send the packet to the first SFF in
  * the identified SFP for forwarding along an SFP.  If re-classification
  * occurs, and that re-classification results in a new SPI, the
  * (re)classifier is, in effect, the initial classifier for the
  * resultant SPI.
  *
  * The SI is used in conjunction the with Service Path Identifier for
  * Service Function Path Selection and for determining the next SFF/SF
  * in the path.  The SI is also valuable when troubleshooting or
  * reporting service paths.  Additionally, while the TTL field is the
  * main mechanism for service plane loop detection, the SI can also be
  * used for detecting service plane loops.
  *
  * When the Base Header specifies MD Type = 0x1, a Fixed Length Context
  * Header (16-bytes) MUST be present immediately following the Service
  * Path Header. The value of a Fixed Length Context
  * Header that carries no metadata MUST be set to zero.
  *
  * When the base header specifies MD Type = 0x2, zero or more Variable
  * Length Context Headers MAY be added, immediately following the
  * Service Path Header (see Figure 5).  Therefore, Length = 0x2,
  * indicates that only the Base Header followed by the Service Path
  * Header are present.  The optional Variable Length Context Headers
  * MUST be of an integer number of 4-bytes.  The base header Length
  * field MUST be used to determine the offset to locate the original
  * packet or frame for SFC nodes that require access to that
  * information.
  *
  * The format of the optional variable length Context Headers
  *
  *  0                   1                   2                   3
  *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  * |          Metadata Class       |      Type     |U|    Length   |
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  * |                      Variable Metadata                        |
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  *
  * Metadata Class (MD Class): Defines the scope of the 'Type' field to
  * provide a hierarchical namespace.  The IANA Considerations
  * Section 11.2.4 defines how the MD Class values can be allocated to
  * standards bodies, vendors, and others.
  *
  * Type: Indicates the explicit type of metadata being carried.  The
  * definition of the Type is the responsibility of the MD Class owner.
  *
  * Unassigned bit: One unassigned bit is available for future use. This
  * bit MUST NOT be set, and MUST be ignored on receipt.
  *
  * Length: Indicates the length of the variable metadata, in bytes.  In
  * case the metadata length is not an integer number of 4-byte words,
  * the sender MUST add pad bytes immediately following the last metadata
  * byte to extend the metadata to an integer number of 4-byte words.
  * The receiver MUST round up the length field to the nearest 4-byte
  * word boundary, to locate and process the next field in the packet.
  * The receiver MUST access only those bytes in the metadata indicated
  * by the length field (i.e., actual number of bytes) and MUST ignore
  * the remaining bytes up to the nearest 4-byte word boundary.  The
  * Length may be 0 or greater.
  *
  * A value of 0 denotes a Context Header without a Variable Metadata
  * field.
  *
  * [0] https://datatracker.ietf.org/doc/draft-ietf-sfc-nsh/
  */
 
 /**
  * struct nsh_md1_ctx - Keeps track of NSH context data
  * @nshc<1-4>: NSH Contexts.
  */
 struct nsh_md1_ctx {
     __be32 context[4];
 };
 
 struct nsh_md2_tlv {
     __be16 md_class;
     u8 type;
     u8 length;
     u8 md_value[];
 };
 
 struct nshhdr {
     __be16 ver_flags_ttl_len;
     u8 mdtype;
     u8 np;
     __be32 path_hdr;
     union {
         struct nsh_md1_ctx md1;
         struct nsh_md2_tlv md2;
     };
 };
 
 /* Masking NSH header fields. */
 #define NSH_VER_MASK       0xc000
 #define NSH_VER_SHIFT      14
 #define NSH_FLAGS_MASK     0x3000
 #define NSH_FLAGS_SHIFT    12
 #define NSH_TTL_MASK       0x0fc0
 #define NSH_TTL_SHIFT      6
 #define NSH_LEN_MASK       0x003f
 #define NSH_LEN_SHIFT      0
 
 #define NSH_MDTYPE_MASK    0x0f
 #define NSH_MDTYPE_SHIFT   0
 
 #define NSH_SPI_MASK       0xffffff00
 #define NSH_SPI_SHIFT      8
 #define NSH_SI_MASK        0x000000ff
 #define NSH_SI_SHIFT       0
 
 /* MD Type Registry. */
 #define NSH_M_TYPE1     0x01
 #define NSH_M_TYPE2     0x02
 #define NSH_M_EXP1      0xFE
 #define NSH_M_EXP2      0xFF
 
 /* NSH Base Header Length */
 #define NSH_BASE_HDR_LEN  8
 
 /* NSH MD Type 1 header Length. */
 #define NSH_M_TYPE1_LEN   24
 
 /* NSH header maximum Length. */
 #define NSH_HDR_MAX_LEN 256
 
 /* NSH context headers maximum Length. */
 #define NSH_CTX_HDRS_MAX_LEN 248
 
 static inline struct nshhdr *nsh_hdr(struct sk_buff *skb)
 {
     return (struct nshhdr *)skb_network_header(skb);
 }
 
 static inline u16 nsh_hdr_len(const struct nshhdr *nsh)
 {
     return ((ntohs(nsh->ver_flags_ttl_len) & NSH_LEN_MASK)
         >> NSH_LEN_SHIFT) << 2;
 }
 
 static inline u8 nsh_get_ver(const struct nshhdr *nsh)
 {
     return (ntohs(nsh->ver_flags_ttl_len) & NSH_VER_MASK)
         >> NSH_VER_SHIFT;
 }
 
 static inline u8 nsh_get_flags(const struct nshhdr *nsh)
 {
     return (ntohs(nsh->ver_flags_ttl_len) & NSH_FLAGS_MASK)
         >> NSH_FLAGS_SHIFT;
 }
 
 static inline u8 nsh_get_ttl(const struct nshhdr *nsh)
 {
     return (ntohs(nsh->ver_flags_ttl_len) & NSH_TTL_MASK)
         >> NSH_TTL_SHIFT;
 }
 
 static inline void __nsh_set_xflag(struct nshhdr *nsh, u16 xflag, u16 xmask)
 {
     nsh->ver_flags_ttl_len
         = (nsh->ver_flags_ttl_len & ~htons(xmask)) | htons(xflag);
 }
 
 static inline void nsh_set_flags_and_ttl(struct nshhdr *nsh, u8 flags, u8 ttl)
 {
     __nsh_set_xflag(nsh, ((flags << NSH_FLAGS_SHIFT) & NSH_FLAGS_MASK) |
                  ((ttl << NSH_TTL_SHIFT) & NSH_TTL_MASK),
             NSH_FLAGS_MASK | NSH_TTL_MASK);
 }
 
 static inline void nsh_set_flags_ttl_len(struct nshhdr *nsh, u8 flags,
                      u8 ttl, u8 len)
 {
     len = len >> 2;
     __nsh_set_xflag(nsh, ((flags << NSH_FLAGS_SHIFT) & NSH_FLAGS_MASK) |
                  ((ttl << NSH_TTL_SHIFT) & NSH_TTL_MASK) |
                  ((len << NSH_LEN_SHIFT) & NSH_LEN_MASK),
             NSH_FLAGS_MASK | NSH_TTL_MASK | NSH_LEN_MASK);
 }
 
 int nsh_push(struct sk_buff *skb, const struct nshhdr *pushed_nh);
 int nsh_pop(struct sk_buff *skb);
 
 #endif /* __NET_NSH_H */

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