getsockopt, setsockopt — get and set options on sockets
#include <sys/types.h> /* See NOTES */ #include <sys/socket.h>
int getsockopt( |
int sockfd, |
| int level, | |
| int optname, | |
| void *optval, | |
socklen_t *optlen); |
int setsockopt( |
int sockfd, |
| int level, | |
| int optname, | |
| const void *optval, | |
socklen_t optlen); |
getsockopt() and
setsockopt() manipulate options
for the socket referred to by the file descriptor sockfd. 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 sockets API level, level is specified as
SOL_SOCKET. To manipulate
options at any other level the protocol number of the
appropriate protocol controlling 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(3).
The arguments optval and optlen are used to access
option values for setsockopt().
For getsockopt() they identify
a buffer in which the value for the requested option(s) are
to be returned. For getsockopt(), optlen is a value-result
argument, 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
NULL.
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 appropriate entries in
section 4 of the manual.
Most socket-level options utilize an int argument for optval. For setsockopt(), the argument should be
nonzero to enable a boolean option, or zero if the option is
to be disabled.
For a description of the available socket options see socket(7) and the appropriate protocol man pages.
On success, zero is returned. On error, −1 is
returned, and errno is set
appropriately.
The argument sockfd is not a valid
descriptor.
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.
optlen
invalid in setsockopt().
In some cases this error can also occur for an invalid
value in optval
(e.g., for the IP_ADD_MEMBERSHIP option described in
ip(7)).
The option is unknown at the level indicated.
The argument sockfd is a file, not a
socket.
POSIX.1-2001 does not require the inclusion of
<sys/types.h> and this header file is not required on
Linux. However, some historical (BSD) implementations
required this header file, and portable applications are
probably wise to include it.
The optlen
argument of getsockopt() and
setsockopt() is in reality an
int [*] (and this is
what 4.x BSD and libc4 and libc5 have). Some POSIX confusion
resulted in the present socklen_t,
also used by glibc. See also accept(2).
This page is part of release 3.24 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man-pages/.
|
Copyright (c) 1983, 1991 The Regents of the University of California. All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. 3. All advertising materials mentioning features or use of this software must display the following acknowledgement: This product includes software developed by the University of California, Berkeley and its contributors. 4. Neither the name of the University nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. $Id: getsockopt.2,v 1.1 1999/05/24 14:57:04 freitag Exp $ Modified Sat Jul 24 16:19:32 1993 by Rik Faith (faithcs.unc.edu) Modified Mon Apr 22 02:29:06 1996 by Martin Schulze (joeyinfodrom.north.de) Modified Tue Aug 27 10:52:51 1996 by Andries Brouwer (aebcwi.nl) Modified Thu Jan 23 13:29:34 1997 by Andries Brouwer (aebcwi.nl) Modified Sun Mar 28 21:26:46 1999 by Andries Brouwer (aebcwi.nl) Modified 1999 by Andi Kleen <akmuc.de>. Removed most stuff because it is in socket.7 now. |