getsockopt, setsockopt — get and set options on sockets
#include <sys/types.h> #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.
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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