getsockopt - Get socket options
#include <sys/socket.h>
int getsockopt(
int socket,
int level,
int option_nam,
void *option_value,
socklen_t *option_len );
[XNS4.0] The definition of the getsockopt() function in
XNS4.0 uses a size_t data type instead of a socklen_t data
type as specified in XNS5.0 (the previous definition).
[Tru64 UNIX] The following definition of the getsockopt()
function does not conform to current standards and is supported
only for backward compatibility (see standards(5)):
int getsockopt(
int socket,
int level,
int option_nam,
char *option_value,
int *option_len );
Interfaces documented on this reference page conform to
industry standards as follows:
getsockopt(): XNS4.0, XNS5.0
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Specifies the file descriptor for the socket. Specifies
the protocol level at which the option resides. To
retrieve options at the socket level, specify the level
parameter as SOL_SOCKET. To retrieve options at other levels,
supply the appropriate protocol number for the protocol
controlling the option. For example, to indicate that
an option will be interpreted by the TCP protocol, set
level to the protocol number of TCP, as defined in the
netinet/in.h header file, or as determined by using the
getprotobyname() function. Specifies a single option to
be retrieved. The socket level options can be enabled or
disabled by the setsockopt() function. The getsockopt()
function retrieves information about the following
options: Reports whether socket listening is enabled. This
option returns an int value. Reports whether transmission
of broadcast messages is supported. This option returns an
int value. [Tru64 UNIX] In a cluster, reports whether
the socket will use the default cluster alias as its
source address. [Tru64 UNIX] In a cluster, reports
whether the socket can only receive packets addressed to
this cluster member. [Tru64 UNIX] In a cluster, reports
whether the socket must receive packets addressed to a
cluster alias and will drop any packets that are not
addressed to a cluster alias. Reports whether debugging
information is being recorded. This option returns an int
value. Reports whether outgoing messages should bypass
the standard routing facilities. The destination must be
on a directly-connected network; messages are directed to
the appropriate network interface. The protocol in use
determines the effect of this option. (Not recommended,
for debugging purposes only.) This option returns an int
value. Reports information about error status and clears
it. This option returns an int value. Reports whether
connections are kept active with periodic transmission of
messages. If the connected socket fails to respond to
these messages, the connection is broken and processes
using that socket are notified with a SIGPIPE signal. This
option returns an int value. Reports whether the socket
lingers on a close() function if data is present. If
SO_LINGER is set, the system blocks the process during the
close() function until it can transmit the data or until
the time expires. If SO_LINGER is not specified, and a
close() function is issued, the system handles the call in
a way that allows the process to continue as quickly as
possible. This option returns an struct linger value.
Reports whether the socket leaves received out-of-band
data (data marked urgent) in line. This option returns an
int value. Reports receive buffer size information. This
option returns an int value. Reports the minimum number
of bytes (low-water mark) for socket receive operations.
The default value is 1. If the value is set to a larger
value, blocking receive calls wait until they receive
either the low water mark value or the requested value
(whichever is smaller). The calls might return less than
the water mark if an error occurs, a signal is received,
or type of data in the receive queue is different than
that returned. This option returns an int value. Reports
receive time-out information. This option returns a
struct timeval value that specifies the amount of time to
wait for a receive operation to complete. If a receive
operation has blocked for the specified amount of time
without receiving additional data, it returns with a partial
error count or errno set to [EAGAIN] or [EWOULDBLOCK].
The default is 0 (zero), which indicates that a
receive operation will not time out. [Tru64 UNIX] In a
cluster, reports whether an attempt to bind the socket to
a port in the reserved range (512-1024) will fail if the
port is marked static. Reports whether the rules used in
validating addresses supplied by a bind() function should
allow reuse of local addresses. This option returns an int
value. [Tru64 UNIX] In a cluster, reports whether the
socket can reuse a locked cluster alias port. Reports
send buffer size information. This option returns an int
value. Reports the minimum number of bytes (low-water
mark) for socket transmit operations. Non-blocking transmit
operations process no data if flow control does not
allow either the send low water mark value or the entire
request (whichever is smaller) to be processed. This
option returns an int value. Reports send time-out information.
This option returns a struct timeval value that
specifies the amount of time a transmit function blocks
when flow control prevents the transmission of data. If a
transmit operation blocks for this amount of time without
transmitting data, it returns with a partial error count
or errno set to [EAGAIN] or [EWOULDBLOCK]. The default is
0 (zero), which indicates that a transmit operation will
not time out. Reports the socket type. This option
returns an int value. Only valid for routing sockets.
Reports whether the sender receives a copy of each message.
This option returns an int value.
[Tru64 UNIX] Options at other protocol levels
vary in format and name. See the tcp(7) and ip(7)
reference pages for more information on option
names relevant for TCP and IP options respectively.
Note
[Tru64 UNIX] The default values for socket
level options like SO_SENDBUF, SO_RCVBUF, SO_SNDLOWAT,
and SO_RCVLOWAT are not constant across different
protocols and implementations. Use the getsockopt(2) routine to obtain the default values
programmatically. The address of a buffer. Specifies
the length of buffer pointed to by
option_value. The option_len parameter initially
contains the size of the buffer pointed to by the
option_value parameter. On return, the option_len
parameter is modified to indicate the actual size
of the value returned. If no option value is supplied
or returned, the option_value parameter can
be 0 (zero). Options at other protocol levels vary
in format and name.
The getsockopt() function allows an application program to
query socket options. The calling program specifies the
name of the socket, the name of the option, and a place to
store the requested information. The operating system gets
the socket option information from its internal data
structures and passes the requested information back to
the calling program.
Options may exist at multiple protocol levels. They are
always present at the uppermost socket level. When
retrieving socket options, specify the level at which the
option resides and the name of the option.
Upon successful completion, the getsockopt() function
returns a value of 0 (zero). Otherwise, a value of -1 is
returned, and errno is set to indicate the error.
If the getsockopt() function fails, errno may be set to
one of the following values: The calling process does not
have appropriate permissions. The socket parameter is not
valid. [POSIX] The send and receive timeout values are
too large to fit in the timeout fields of the socket
structure. The address pointed to by the option_value
parameter is not in a valid (writable) part of the process
space, or the option_len parameter is not in a valid part
of the process address space. The option_value or
option_len parameter is invalid; or the socket is shut
down. Insufficient resources are available in the system
to complete the call. The option is unknown. The available
STREAMS resources were insufficient for the operation
to complete. The socket parameter refers to a file, not a
socket. [XNS4.0] The operation is not supported by the
socket protocol.
Functions: bind(2), close(2), endprotoent(3), getprotobynumber(3), getprotoent(3), setprotoent(3), setsockopt(2), socket(2).
NetworkInformation: ip(7), tcp(7).
Standards: standards(5).
Network Programmer's Guide
getsockopt(2)
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