net: add NSH header structures and helpers

#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);

}

#endif /* __NET_NSH_H */