getsockopt, setsockopt — get and set options on sockets
#include <sys/types.h> /* See NOTES */ #include <sys/socket.h>
int
getsockopt( |
int | s, |
int | level, | |
int | optname, | |
void * | optval, | |
socklen_t * | optlen) ; |
int
setsockopt( |
int | s, |
int | level, | |
int | optname, | |
const void * | optval, | |
socklen_t | optlen) ; |
getsockopt
() and
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
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 parameters 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
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 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 optval
. For 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.
On success, zero is returned. On error, −1 is
returned, and errno
is set
appropriately.
The argument s
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
().
The option is unknown at the level indicated.
The argument s
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).
ioctl(2), socket(2), getprotoent(3), protocols(5), socket(7), tcp(7), unix(7)
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