Tribblix: manual page: getsockopt.3socket

GETSOCKOPT(3SOCKET) Sockets Library Functions GETSOCKOPT(3SOCKET)

NAME

getsockopt, setsockopt - get and set options on sockets

SYNOPSIS

cc [ flag ... ] file ... -lsocket -lnsl [ library ... ]
#include <sys/types.h>
#include <sys/socket.h>

int getsockopt(int s, int level, int optname, void *optval,
int *optlen);

int setsockopt(int s, int level, int optname, const void *optval,
int optlen);

DESCRIPTION

The getsockopt() and setsockopt() functions manipulate options
associated with a socket. Options may exist at multiple protocol
levels; they are always present at the uppermost "socket" level.

The level argument specifies the protocol level at which the option
resides. To manipulate options at the socket level, specify the level
argument as SOL_SOCKET. To manipulate options at the protocol level,
supply the appropriate protocol number for the protocol controlling
the option. For example, to indicate that an option will be
interpreted by the TCP, set level to the protocol number of TCP, as
defined in the <netinet/in.h> header, or as determined by using
getprotobyname(3SOCKET). Some socket protocol families may also
define additional levels, such as SOL_ROUTE. Only socket-level
options are described here.

The parameters optval and optlen are used to access option values for
setsockopt(). For getsockopt(), they identify a buffer in which the
value(s) 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. Use a 0
optval if no option value is to be supplied or returned.

The optname and any specified options are passed uninterpreted to the
appropriate protocol module for interpretation. The include file
<sys/socket.h> contains definitions for the socket-level options
described below. Options at other protocol levels vary in format and
name.

Most socket-level options take an int for optval. For setsockopt(),
the optval parameter should be non-zero to enable a boolean option,
or zero if the option is to be disabled. SO_LINGER uses a struct
linger parameter that specifies the desired state of the option and
the linger interval. struct linger is defined in <sys/socket.h>.
struct linger contains the following members:

l_onoff
on = 1/off = 0

l_linger
linger time, in seconds

The following options are recognized at the socket level. Except as
noted, each may be examined with getsockopt() and set with
setsockopt().

SO_DEBUG
enable/disable recording of debugging information

SO_REUSEADDR
enable/disable local address reuse

SO_KEEPALIVE
enable/disable keep connections alive

SO_DONTROUTE
enable/disable routing bypass for outgoing
messages

SO_LINGER
linger on close if data is present

SO_BROADCAST
enable/disable permission to transmit broadcast
messages

SO_OOBINLINE
enable/disable reception of out-of-band data in
band

SO_SNDBUF
set buffer size for output

SO_RCVBUF
set buffer size for input

SO_DGRAM_ERRIND
application wants delayed error

SO_TIMESTAMP
enable/disable reception of timestamp with
datagrams

SO_EXCLBIND
enable/disable exclusive binding of the socket

SO_TYPE
get the type of the socket (get only)

SO_ERROR
get and clear error on the socket (get only)

SO_MAC_EXEMPT
get or set mandatory access control on the socket.
This option is available only when the system is
configured with Trusted Extensions.

SO_ALLZONES
bypass zone boundaries (privileged).

SO_DOMAIN
get the domain used in the socket (get only)

SO_PROTOTYPE, SO_PROTOCOL
Get the protocol used in the socket. This may not
be the protocol passed in during a call to
socket(3SOCKET). For example, when protocol 0 is
used with sockets in the domain, PF_INET and
PF_INET6, this will return the underlying protocol
that is in use, such as IPPROTO_TCP. SO_PROTOCOL
is the standard POSIX name for this option.
SO_PROTOTYPE is the traditional operating system
name for this option. Most sockets do not support
setting this option.

The SO_DEBUG option enables debugging in the underlying protocol
modules. The SO_REUSEADDR option indicates that the rules used in
validating addresses supplied in a bind(3SOCKET) call should allow
reuse of local addresses. The SO_KEEPALIVE option enables the
periodic transmission of messages on a connected socket. If the
connected party fails to respond to these messages, the connection is
considered broken and threads using the socket are notified using a
SIGPIPE signal. The SO_DONTROUTE option indicates that outgoing
messages should bypass the standard routing facilities. Instead,
messages are directed to the appropriate network interface according
to the network portion of the destination address.

The SO_LINGER option controls the action taken when unsent messages
are queued on a socket and a close(2) is performed. If the socket
promises reliable delivery of data and SO_LINGER is set, the system
will block the thread on the close() attempt until it is able to
transmit the data or until it decides it is unable to deliver the
information (a timeout period, termed the linger interval, is
specified in the setsockopt() call when SO_LINGER is requested). If
SO_LINGER is disabled and a close() is issued, the system will
process the close() in a manner that allows the thread to continue as
quickly as possible.

The option SO_BROADCAST requests permission to send broadcast
datagrams on the socket. With protocols that support out-of-band
data, the SO_OOBINLINE option requests that out-of-band data be
placed in the normal data input queue as received; it will then be
accessible with recv() or read() calls without the MSG_OOB flag.

The SO_SNDBUF and SO_RCVBUF options adjust the normal buffer sizes
allocated for output and input buffers, respectively. The buffer size
may be increased for high-volume connections or may be decreased to
limit the possible backlog of incoming data. The maximum buffer size
for UDP is determined by the value of the ndd variable udp_max_buf.
The maximum buffer size for TCP is determined the value of the ndd
variable tcp_max_buf. Use the ndd(8) utility to determine the current
default values. See the Solaris Tunable Parameters Reference Manual
for information on setting the values of udp_max_buf and tcp_max_buf.
At present, lowering SO_RCVBUF on a TCP connection after it has been
established has no effect.

By default, delayed errors (such as ICMP port unreachable packets)
are returned only for connected datagram sockets. The SO_DGRAM_ERRIND
option makes it possible to receive errors for datagram sockets that
are not connected. When this option is set, certain delayed errors
received after completion of a sendto() or sendmsg() operation will
cause a subsequent sendto() or sendmsg() operation using the same
destination address (to parameter) to fail with the appropriate
error. See send(3SOCKET).

If the SO_TIMESTAMP option is enabled on a SO_DGRAM or a SO_RAW
socket, the recvmsg(3XNET) call will return a timestamp in the native
data format, corresponding to when the datagram was received.

The SO_EXCLBIND option is used to enable or disable the exclusive
binding of a socket. It overrides the use of the SO_REUSEADDR option
to reuse an address on bind(3SOCKET). The actual semantics of the
SO_EXCLBIND option depend on the underlying protocol. See tcp(4P) or
udp(4P) for more information.

The SO_TYPE and SO_ERROR options are used only with getsockopt(). The
SO_TYPE option returns the type of the socket, for example,
SOCK_STREAM. It is useful for servers that inherit sockets on
startup. The SO_ERROR option returns any pending error on the socket
and clears the error status. It may be used to check for asynchronous
errors on connected datagram sockets or for other asynchronous
errors.

The SO_MAC_EXEMPT option is used to toggle socket behavior with
unlabeled peers. A socket that has this option enabled can
communicate with an unlabeled peer if it is in the global zone or has
a label that dominates the default label of the peer. Otherwise, the
socket must have a label that is equal to the default label of the
unlabeled peer. Calling setsockopt() with this option returns an
EACCES error if the process lacks the NET_MAC_AWARE privilege or if
the socket is bound. The SO_MAC_EXEMPT option is available only when
the system is configured with Trusted Extensions.

The SO_ALLZONES option can be used to bypass zone boundaries between
shared-IP zones. Normally, the system prevents a socket from being
bound to an address that is not assigned to the current zone. It also
prevents a socket that is bound to a wildcard address from receiving
traffic for other zones. However, some daemons which run in the
global zone might need to send and receive traffic using addresses
that belong to other shared-IP zones. If set before a socket is
bound, SO_ALLZONES causes the socket to ignore zone boundaries
between shared-IP zones and permits the socket to be bound to any
address assigned to the shared-IP zones. If the socket is bound to a
wildcard address, it receives traffic intended for all shared-IP
zones and behaves as if an equivalent socket were bound in each
active shared-IP zone. Applications that use the SO_ALLZONES option
to initiate connections or send datagram traffic should specify the
source address for outbound traffic by binding to a specific address.
There is no effect from setting this option in an exclusive-IP zone.
Setting this option requires the sys_net_config privilege. See
zones(7).

RETURN VALUES

If successful, getsockopt() and setsockopt() return 0. Otherwise,
the functions return -1 and set errno to indicate the error.

ERRORS

The getsockopt() and setsockopt() calls succeed unless:

EBADF
The argument s is not a valid file descriptor.

ENOMEM
There was insufficient memory available for the
operation to complete.

ENOPROTOOPT
The option is unknown at the level indicated.

ENOSR
There were insufficient STREAMS resources available
for the operation to complete.

ENOTSOCK
The argument s is not a socket.

ENOBUFS
SO_SNDBUF or SO_RCVBUF exceeds a system limit.

EINVAL
Invalid length for a given socket option.

EHOSTUNREACH
Invalid address for IP_MULTICAST_IF.

EINVAL
Not a multicast address for IP_ADD_MEMBERSHIP and
IP_DROP_MEMBERSHIP.

EADDRNOTAVAIL
Bad interface address for IP_ADD_MEMBERSHIP and
IP_DROP_MEMBERSHIP.

EADDRINUSE
Address already joined for IP_ADD_MEMBERSHIP.

ENOENT
Address not joined for IP_DROP_MEMBERSHIP.

EPERM
No permissions.

EACCES
Permission denied.

EINVAL
The specified option is invalid at the specified
socket level, or the socket has been shut down.