getsockopt
NAME
getsockopt, setsockopt - get and set options on sockets
SYNOPSIS
R #include <sys/types.h> /* See NOTES */
#include <sys/socket.h> I int getsockopt(int s , int level , int optname , I void * optval , socklen_t * optlen ); I int setsockopt(int s , int level , int optname , I const void * optval , socklen_t optlen );
DESCRIPTION
R getsockopt ()
and
R setsockopt ()
manipulate the
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
R 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
R TCP ;
see
getprotoent(3).
The parameters
optval
and
optlen
are used to access option values for
R setsockopt ().
For
R getsockopt ()
they identify a buffer in which the value for the
requested option(s) are to be returned.
For
R getsockopt (),
optlen
is a value-result parameter, initially containing the
size of the buffer pointed to by
R 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
parameter for
R optval .
For
R setsockopt (),
the parameter should be non-zero 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.
RETURN VALUE
On success, zero is returned.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
EBADF
The argument
s
is not a valid descriptor.
EFAULT
The address pointed to by
optval
is not in a valid part of the process address space.
For
R getsockopt (),
this error may also be returned if
optlen
is not in a valid part of the process address space.
EINVAL
optlen
invalid in
R setsockopt ().
ENOPROTOOPT
The option is unknown at the level indicated.
ENOTSOCK
The argument
s
is a file, not a socket.
CONFORMING TO
SVr4, 4.4BSD (these system calls first appeared in 4.2BSD),
POSIX.1-2001.
NOTES
POSIX.1-2001 does not require the inclusion of
R <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
R getsockopt ()
and
R 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
R socklen_t ,
also used by glibc.
See also
accept(2).
BUGS
Several of the socket options should be handled at lower levels of the
system.
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