HP 3000 Manuals HP 3000 Manuals
GETSOCKOPT, SETSOCKOPT
C Interface
#include <sys/socket.h>
int getsockopt(
int s,
int level,
int optname,
void *optval,
int *optlen);
int setsockopt(
int s,
int level,
int optname,
const void *optval,
int optlen);
Description
getsockopt and setsockopt manipulate options associated with a socket.
The socket is identified by the socket descriptor s. Options can exist
at multiple protocol levels. Options are described below under the
appropriate option.
When manipulating socket options, the level at which the option resides
(level) and the name of the option (optname) must be specified. To
manipulate options at the "socket" level, level is specified as
SOL_SOCKET.
There are two kinds of options: boolean and non-boolean. Boolean
options are either set or not set and also can use optval and optlen (see
below) to pass information. Non-boolean options always use optval and
optlen to pass information.
To determine whether or not a boolean option is set, the return value of
getsockopt must be examined. If the option is set, getsockopt returns
without error. If the boolean option is not set, getsockopt returns -1
and errno is set to ENOPROTOOPT.
For setsockopt, the parameters optval and optlen are used to pass option
information from the calling process to the system. optval is the
address of a location in memory that contains the option information to
be passed to the system. optlen is an integer that specifies the size in
bytes of the option information.
For getsockopt, optval and optlen are used to pass option information
from the system to the calling process. optval is the address of a
location in memory that contains the option information to be passed to
the calling process, or (char *) NULL if the option information is not of
interest and not to be passed to the calling process. optlen is an
address of an integer initially used to specify the maximum number of
bytes of option information to be passed. If optval is not (char *)
NULL, optlen is set on return to the actual number of bytes of option
information passed. If the getsockopt call fails, no option information
is passed.
optname and any specified options are passed uninterpreted to the
appropriate protocol module for interpretation. The include file
<sys/socket.h> contains definitions for "socket" level options. Options
at other protocol levels vary in format and name.
The "socket" level options defined in the include file <sys/socket.h> are
explained below.
SOL_SOCKETS
When the socket level is SOL_SOCKETS, the following options are
available:
SO_DEBUG (Boolean option) No functionality; included only for
compatibility.
SO_KEEPALIVE (Boolean option; AF_INET SOCK_STREAM sockets only)
Keeps otherwise idle connected sockets active by
forcing transmissions every 600 seconds for up to
four retransmissions without a response. The length
of time and number of retransmissions are
configurable in NMMGR.
Default: Off
SO_LINGER (Boolean option; AF_INET SOCK_STREAM sockets only)
Lingers on close if data is present. For SO_LINGER,
optval points to a struct linger, defined in
<sys/socket.h>. The linger structure contains an
integer boolean flag to toggle behavior on/off and an
integer linger value.
Default: Off
SO_BROADCAST (Boolean option; AF_INET SOCK_DGRAM sockets only)
Toggles permission to transmit broadcast messages.
Default: Off
SO_ERROR Returns to the caller the last error stored in the
socket record. This error variable is then cleared
in the socket record.
SO_TYPE Returns the socket type. This option is typically
used by a process that inherits a socket when it is
started.
SO_LINGER controls the actions taken when unsent messages are queued on a
SOCK_STREAM socket and a close is performed. If SO_LINGER is toggled on
with a non-zero linger interval, the system blocks the process on the
close attempt until it is able to transmit the data or until it decides
it is unable to deliver the information. If SO_LINGER is toggled on with
a linger interval of zero, the connection is immediately terminated on
the close of the socket, and any unsent data queued on the connection is
lost. If SO_LINGER is toggled off (default upon socket creation) and a
close is issued, the call returns immediately. The system still
gracefully brings down the connection by transmitting any queued data, if
possible. SO_LINGER can be toggled on/off at any time during the life of
an established connection. Toggling SO_LINGER does not affect the action
of shutdown.
The SO_BROADCAST option requests permission to send internet broadcast
datagrams on the socket.
The ip level option defined in the include file <netinet/in.h> is
explained below.
IPPROTO_IP
When the socket level is IPPROTO_IP, the following option is available:
IP_OPTIONS (AF_INET SOCK_DGRAM) Allows you to set and retrieve
direct IP header information.
IPPROTO_UDP
No options are defined for this level.
The tcp level option defined in the include file <netinet/tcp.h> is
described below.
IPPROTO_TCP
When the socket level is IPPROTO_TCP, the following option is available:
TCP_MAXSEG (AF_INET SOCK_STREAM) Returns the maximum segment
size in use for the socket. It defaults the size to
536 until the socket is connected. The size is
negotiated during connection establishment.
Return Value
If the call is successful, 0 is returned. If it fails, -1 is returned
and an error code is stored in errno.
Errors
The call to getsockopt or setsockopt fails if:
[EBADF] The argument s is not a valid descriptor.
[EOPNOTSUPP] The option is not supported by the protocol in use by
the socket.
[ENOBUFS] No buffer space is available.
[ENOTSOCK] The argument s is a file, not a socket.
[ENOPROTOOPT] In getsockopt, the requested option is currently not
set.
[EINVAL] The option is unknown at the socket level or the
socket has been shut down.
[EFAULT] The optval or, in the case of getsockopt, optlen
parameters are not valid pointers.
[ESOCKTNOSUPPORT] The socket is a NetIPC socket.
Author
UCB (University of California at Berkeley)
See Also
socket, getprotoent