nf_conntrack_proto_gre.h

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#ifndef _CONNTRACK_PROTO_GRE_H
#define _CONNTRACK_PROTO_GRE_H
#include <asm/byteorder.h>

/* GRE PROTOCOL HEADER */

/* GRE Version field */
#define GRE_VERSION_1701    0x0
#define GRE_VERSION_PPTP    0x1

/* GRE Protocol field */
#define GRE_PROTOCOL_PPTP   0x880B

/* GRE Flags */
#define GRE_FLAG_C      0x80
#define GRE_FLAG_R      0x40
#define GRE_FLAG_K      0x20
#define GRE_FLAG_S      0x10
#define GRE_FLAG_A      0x80

#define GRE_IS_C(f) ((f)&GRE_FLAG_C)
#define GRE_IS_R(f) ((f)&GRE_FLAG_R)
#define GRE_IS_K(f) ((f)&GRE_FLAG_K)
#define GRE_IS_S(f) ((f)&GRE_FLAG_S)
#define GRE_IS_A(f) ((f)&GRE_FLAG_A)

/* GRE is a mess: Four different standards */
struct gre_hdr {
#if defined(__LITTLE_ENDIAN_BITFIELD)
    __u16   rec:3,
        srr:1,
        seq:1,
        key:1,
        routing:1,
        csum:1,
        version:3,
        reserved:4,
        ack:1;
#elif defined(__BIG_ENDIAN_BITFIELD)
    __u16   csum:1,
        routing:1,
        key:1,
        seq:1,
        srr:1,
        rec:3,
        ack:1,
        reserved:4,
        version:3;
#else
#error "Adjust your <asm/byteorder.h> defines"
#endif
    __be16  protocol;
};

/* modified GRE header for PPTP */
struct gre_hdr_pptp {
    __u8   flags;       /* bitfield */
    __u8   version;     /* should be GRE_VERSION_PPTP */
    __be16 protocol;    /* should be GRE_PROTOCOL_PPTP */
    __be16 payload_len; /* size of ppp payload, not inc. gre header */
    __be16 call_id;     /* peer's call_id for this session */
    __be32 seq;     /* sequence number.  Present if S==1 */
    __be32 ack;     /* seq number of highest packet received by */
                /*  sender in this session */
};

struct nf_ct_gre {
    unsigned int stream_timeout;
    unsigned int timeout;
};

#ifdef __KERNEL__
#include <net/netfilter/nf_conntrack_tuple.h>

struct nf_conn;

/* structure for original <-> reply keymap */
struct nf_ct_gre_keymap {
    struct list_head list;
    struct nf_conntrack_tuple tuple;
};

/* add new tuple->key_reply pair to keymap */
int nf_ct_gre_keymap_add(struct nf_conn *ct, enum ip_conntrack_dir dir,
             struct nf_conntrack_tuple *t);

/* delete keymap entries */
void nf_ct_gre_keymap_destroy(struct nf_conn *ct);

extern void nf_ct_gre_keymap_flush(struct net *net);
extern void nf_nat_need_gre(void);

#endif /* __KERNEL__ */
#endif /* _CONNTRACK_PROTO_GRE_H */