getsockopt(2) getsockopt(2)
NAME
getsockopt, setsockopt - get and set options on sockets
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
getsockopt(s, level, optname, optval, optlen)
int s, level, optname;
char *optval;
int *optlen;
setsockopt(s, level, optname, optval, optlen)
int s, level, optname;
char *optval;
int optlen;
DESCRIPTION
getsockopt and setsockopt manipulate options associated with
a socket. Options may exist at multiple protocol levels;
they are always present at the uppermost ``socket'' level.
When manipulating socket options the level at which the
option resides and the name of the option must be specified.
To manipulate options at the ``socket'' level, level is
specified as SOL_SOCKET. To manipulate options at any other
level the protocol number of the appropriate protocol con-
trolling the option is supplied. For example, to indicate
that an option is to be interpreted by the TCP protocol,
level should be set to the protocol number of TCP; see
getprotoent(3N).
The parameters optval and optlen are used to access option
values for setsockopt. Zero should no longer be specified
for these parameters as the option may now be toggled on and
off. Specify a pointer to a non-zero value to enable a
boolean option, and a pointer to a zero value to disable an
option.
For getsockopt optval and optlen identify a buffer in which
the value for the requested option(s) are to be returned.
Optlen is a value-result parameter, initially containing the
size of the buffer pointed to by optval, and modified on
return to indicate the actual size of the value returned.
If no option value is to be supplied or returned, optval may
be supplied as 0.
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, described below. Options at other
protocol levels vary in format and name; consult the
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getsockopt(2) getsockopt(2)
appropriate entries in section (4P).
Most socket-level options take an int parameter for optval.
SO_LINGER uses a struct linger parameter, defined in
<sys/socket.h>, which specifies the desired state of the
option and the linger interval (see below).
The following options are recognized at the socket level.
Except as noted, each may be examined with getsockopt and
set with setsockopt
SO_DEBUG toggle recording of debugging information
SO_REUSEADDR toggle local address reuse
SO_KEEPALIVE toggle keep connections alive
SO_DONTROUTE toggle routing bypass for outgoing messages
SO_LINGER linger on close if data present
SO_BROADCAST toggle permission to transmit broadcast messages
SO_OOBINLINE toggle reception of out-of-band data in band
SO_SNDBUF set buffer size for output
SO_RCVBUF set buffer size for input
SO_MLSATTR set/get the label on a socket (B1 only)
SO_TYPE get the type of the socket (get only)
SO_ERROR get and clear error on the socket (get only)
SO_DEBUG enables debugging in the underlying protocol
modules. SO_REUSEADDR indicates that the rules used in
validating addresses supplied in a bind(2) call should allow
reuse of local addresses. SO_KEEPALIVE enables the periodic
transmission of messages on a connected socket. Should the
connected party fail to respond to these messages, the con-
nection is considered broken and processes using the socket
are notified via a SIGPIPE signal. SO_DONTROUTE indicates
that outgoing messages should bypass the standard routing
facilities. Instead, messages are directed to the appropri-
ate network interface according to the network portion of
the destination address.
SO_LINGER controls the action taken when unsent messages are
queued on socket and a close(2) is performed. If the socket
promises reliable delivery of data and SO_LINGER is set, the
system will block 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 (a timeout period, termed
the linger interval, is specified in the setsockopt call
when SO_LINGER is requested). If SO_LINGER is disabled and a
close is issued, the system will process the close in a
manner that allows the process to continue as quickly as
possible.
The option SO_BROADCAST requests permission to send broad-
cast datagrams on the socket. Broadcast was a privileged
operation in earlier versions of the system. With protocols
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getsockopt(2) getsockopt(2)
that support out-of-band data, the SO_OOBINLINE option
requests that out-of-band data be placed in the normal data
input queue as received; it will then be accessible with
recv or read calls without the MSG_OOB flag. SO_SNDBUF and
SO_RCVBUF are options to adjust the normal buffer sizes
allocated for output and input buffers, respectively. The
buffer size may be increased for high-volume connections, or
may be decreased to limit the possible backlog of incoming
data. The system places an absolute limit on these values.
The SO_MLSATTR option allows for changing or viewing the
label on a socket and is only available on CX/SX B1 systems
configured with secure networking. The label may be set only
if the process is running as super-user. Finally, SO_TYPE
and SO_ERROR are options used only with getsockopt. SO_TYPE
returns the type of the socket, such as SOCK_STREAM; it is
useful for servers that inherit sockets on startup.
SO_ERROR returns any pending error on the socket and clears
the error status. It may be used to check for asynchronous
errors on connected datagram sockets or for other asynchro-
nous errors.
RETURN VALUE
A 0 is returned if the call succeeds, -1 if it fails.
ERRORS
The call succeeds unless:
[EBADF] The argument s is not a valid descrip-
tor.
[ENOTSOCK] The argument s is a file, not a socket.
[ENOPROTOOPT] The option is unknown at the level indi-
cated.
[EFAULT] The address pointed to by optval is not
in a valid part of the process address
space. For getsockopt, this error may
also be returned if optlen is not in a
valid part of the process address space.
NOTE
This call is defined in the 88open Binary and Object Compa-
tibility Standards' Networking Supplements (BCSNS and OCSNS)
for use in BCSNS/OCSNS compliant applications. OCSNS-
defined functions may be accessed by passing OCS options to
cc(1) and ld(1).
SEE ALSO
ioctl(2), socket(2), getprotoent(3N)
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getsockopt(2) getsockopt(2)
BUGS
Several of the socket options should be handled at lower
levels of the system.
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