getsockopt Subroutine

Purpose

Gets options on sockets.

Library

Standard C Library (libc.a)

Syntax

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/atmsock.h> /*Needed for SOCK_CONN_DGRAM socket type only*/

int getsockopt (Socket, Level, OptionName, OptionValue, OptionLength)
int Socket, Level, OptionName;
void *OptionValue;
size_t *OptionLength;

Description

The getsockopt subroutine 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 can exist at multiple protocol levels. They are always present at the uppermost socket level. When retrieving socket options, specify the level where the option resides and the name of the option.

Parameters

Options at other protocol levels vary in format and name.

IP level (IPPROTO_IP level) options are defined as follows:

In the case of TCP protocol sockets:

Return Values

Upon successful completion, the getsockopt subroutine returns a value of 0.

If the getsockopt subroutine is unsuccessful, the subroutine handler performs the following actions:

• Returns a value of -1 to the calling program.
• Moves an error code, indicating the specific error, into the errno global variable.

Upon successful completion of the IPPROTO_IP option IP_PMTUAGE the returns are:

• OptionValue 0 if PMTU discovery is not enabled.
• OptionValue -1 if PMTU discovery is not complete.
• Positive non-zero OptionValue if PMTU is available.

Upon successful completion of TCP protocol sockets option IP_FINDPMTU the returns are:

• OptionValue 0 if PMTU discovery (tcp_pmtu_discover) is not enabled.
• OptionValue -1 if PMTU discovery is not complete/not available.
• Positive non-zero OptionValue if PMTU is available.

Error Codes

The getsockopt subroutine is unsuccessful if any of the following errors occurs:

Examples

The following program fragment illustrates the use of the getsockopt subroutine to determine an existing socket type:

#include <sys/types.h>
#include <sys/socket.h>
int type, size;
size = sizeof(int);
if(getsockopt(s, SOL_SOCKET, SO_TYPE, (char*)&type,&size)<0){
.
.
.
}

Implementation Specifics

The getsockopt subroutine is part of Base Operating System (BOS) Runtime.

All applications containing the getsockopt subroutine must be compiled with _BSD set to a specific value. Acceptable values are 43 and 44. In addition, all socket applications must include the BSD libbsd.a library.

Related Information

The no command.

The bind subroutine, close subroutine, endprotoent subroutine, getprotobynumber subroutine, getprotoent subroutine, setprotoent subroutine, setsockopt subroutine, socket subroutine.

Sockets Overview, Understanding Socket Options, and Understanding Socket Types and Protocols in AIX Version 4.3 Communications Programming Concepts.