This section describes the APIs that include options to modify
the socket behavior.
SCTP provides many socket options to modify options that are
associated with a socket. These socket options can enable or disable
certain functions to facilitate applications to control the transport
of data.
If you modify a socket option, you must specify the level to
which the option belongs. The level indicates whether the option applies
to the socket interface, or to a lower-level communications protocol
interface, such as IP, TCP, or SCTP.
You can use the getsockopt()() and setsockopt()() system calls to modify the socket options.
These system calls set or retrieve socket interface options, or lower-level protocol
options.
Following is the syntax for the getsockopt()() system
call:
int getsockopt(
int s,
int level,
int optname,
void *optval,
int *optlen
);
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where:
- s
Indicates the file descriptor.
- level
Specifies the type of protocol. You must set the level to IPPROTO_SCTP for all the SCTP options.
- optname
Specifies the option name.
- optval
Specifies the buffer to store the value of the option.
- optlen
Specifies the size of the buffer (or the length of
the option returned).
Following is the syntax for the setsockopt()() API:
int setsockopt(
int s,
int level,
int optname,
const void *optval,
int optlen
);
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where:
- s
Indicates the file descriptor.
- level
Specifies the type of protocol. You must set the level
to IPPROTO_SCTP for all SCTP options.
- optname
Specifies the option name.
- optval
Specifies the buffer to store the value of the option.
- optlen
Specifies the size of the buffer (or the length of
the option returned).
SCTP associations being multihomed, certain option parameters
include the sockaddr_storage structure to select
the peer address to which the option must be applied. For a one-to-many
style socket, applications can use an association ID (sctp_assoc_t structure) to identify the association
instance that is affected by the option. Applications must set this
association ID while using a one-to-many API style socket. In the
case of one-to-one style socket APIs and the branched off one-to-many
style sockets, SCTP ignores this association ID parameter.
In the case of the one-to-many style APIs, the socket options
are applied to all associations that belong to a socket. For a one-to-one
API, the socket options apply to all peer addresses of the association
controlled by the socket.
In the SCTP stack, the getsockopt()() is
read-only. This means that applications cannot specify any information
in the getsockopt()() call. As a result, applications
must use the sctp_opt_info()() API to pass information both into
and out of the SCTP stack.
Following is the syntax for the sctp_opt_info()() API:
int sctp_opt_info(int sd,
sctp_assoc_t id,
int opt,
void *arg,
socklen_t *size);
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where:
- id
Specifies the association ID. For a one-to-many style
socket, id specifies the association to query.
For a one-to-one style socket, SCTP ignores the ID.
- opt
Specifies the SCTP socket option. The sctp_opt_info()() API retrieves socket options, specified as follows:
sctp_opt_info()() does not support the authentication
related-options SCTP_AUTH_CHUNKS, SCTP_AUTH_SECRET, and SCTP_PEER_AUTH_CHUNKS.
- arg
Specifies an option-specific structure buffer that
is provided by an application.
The sctp_opt_info()() API returns 0 on success,
and returns -1 on failure. It sets errno to the
appropriate error code.
The sctp_opt_info()() call is a replacement
for getsockopt()(), and sctp_opt_info()() does not set any option associated with the specified socket. You
must use the setsockopt()() call to set any writeable
option, such as SO_LINGER and SCTP_NODELAY.
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