https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86535
--- Comment #4 from Curtis Hamilton <clhamilto at gmail dot com> ---
Here's the definition in sys/socket.h:
/*
* Header for ancillary data objects in msg_control buffer.
* Used for additional information with/about a datagram
* not expressible by flags. The format is a sequence
* of message elements headed by cmsghdr structures.
*/
struct cmsghdr {
socklen_t cmsg_len; /* data byte count, including
hdr */
int cmsg_level; /* originating protocol */
int cmsg_type; /* protocol-specific type */
/* followed by u_char cmsg_data[]; */
};
Here's what is in inet6/in6.h:
struct cmsghdr;
extern int inet6_option_space(int);
extern int inet6_option_init(void *, struct cmsghdr **, int);
extern int inet6_option_append(struct cmsghdr *, const uint8_t *,
int, int);
extern uint8_t *inet6_option_alloc(struct cmsghdr *, int, int, int);
extern int inet6_option_next(const struct cmsghdr *, uint8_t **);
extern int inet6_option_find(const struct cmsghdr *, uint8_t **, int);
extern size_t inet6_rthdr_space(int, int);
extern struct cmsghdr *inet6_rthdr_init(void *, int);
extern int inet6_rthdr_add(struct cmsghdr *, const struct in6_addr *,
unsigned int);
extern int inet6_rthdr_lasthop(struct cmsghdr *, unsigned int);
#if 0 /* not implemented yet */
extern int inet6_rthdr_reverse(const struct cmsghdr *, struct cmsghdr *);
#endif
extern int inet6_rthdr_segments(const struct cmsghdr *);
extern struct in6_addr *inet6_rthdr_getaddr(struct cmsghdr *, int);
extern int inet6_rthdr_getflags(const struct cmsghdr *, int);
extern int inet6_opt_init(void *, socklen_t);
extern int inet6_opt_append(void *, socklen_t, int, uint8_t, socklen_t,
uint8_t, void **);
extern int inet6_opt_finish(void *, socklen_t, int);
extern int inet6_opt_set_val(void *, int, void *, socklen_t);
extern int inet6_opt_next(void *, socklen_t, int, uint8_t *, socklen_t *,
void **);
extern int inet6_opt_find(void *, socklen_t, int, uint8_t, socklen_t *,
void **);
extern int inet6_opt_get_val(void *, int, void *, socklen_t);
extern socklen_t inet6_rth_space(int, int);
extern void *inet6_rth_init(void *, socklen_t, int, int);
extern int inet6_rth_add(void *, const struct in6_addr *);
extern int inet6_rth_reverse(const void *, void *);
extern int inet6_rth_segments(const void *);
extern struct in6_addr *inet6_rth_getaddr(const void *, int);
__END_DECLS
