Comtrol eCos - Manual (Page 538)

Chapter 38. TCP/IP Library Reference
inet6_option_init(void *bp, struct cmsghdr **cmsgp, int type);
int
inet6_option_append(struct cmsghdr *cmsg, const u_int8_t *typep,
int multx, int plusy);
u_int8_t *
inet6_option_alloc(struct cmsghdr *cmsg, int datalen, int multx,
int plusy);;
int
inet6_option_next(const struct cmsghdr *cmsg, u_int8_t **tptrp);
int
inet6_option_find(const struct cmsghdr *cmsg, u_int8_t **tptrp,
int type);
DESCRIPTION
Building and parsing the Hop-by-Hop and Destination options is compli-
cated due to alignment constranints, padding and ancillary data manipula-
tion. RFC2292 defines a set of functions to help the application. The
function prototypes for these functions are all in the < netinet/in.h>
header.
inet6_option_space
inet6_option_space() returns the number of bytes required to hold an
option when it is stored as ancillary data, including the cmsghdr struc-
ture at the beginning, and any padding at the end (to make its size a
multiple of 8 bytes). The argument is the size of the structure defining
the option, which must include any pad bytes at the beginning (the value
y in the alignment term “xn + y”), the type byte, the length byte, and
the option data.
Note: If multiple options are stored in a single ancillary data object,
which is the recommended technique, this function overestimates the
amount of space required by the size of N-1 cmsghdr structures, where N
is the number of options to be stored in the object. This is of little
consequence, since it is assumed that most Hop-by-Hop option headers and
Destination option headers carry only one option (appendix B of
[RFC-2460]).
inet6_option_init
inet6_option_init() is called once per ancillary data object that will
contain either Hop-by-Hop or Destination options. It returns 0 on suc-
cess or -1 on an error.
bp is a pointer to previously allocated space that will contain the
ancillary data object. It must be large enough to contain all the indi-
vidual options to be added by later calls to inet6_option_append() and
inet6_option_alloc().
cmsgp is a pointer to a pointer to a cmsghdr structure. *cmsgp is ini-
tialized by this function to point to the cmsghdr structure constructed
by this function in the buffer pointed to by bp.
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