NAME | SYNOPSIS | API RESTRICTIONS | FEATURES | DESCRIPTION | RETURN VALUES | ATTRIBUTES | SEE ALSO
#include <sys/types.h> #include <sys/socket.h>int getsockopt(int s, int level, int optname, void * optval, socklen_t * optlen);
The function or functions documented here may not be used safely in all application contexts with all APIs provided in the ChorusOS 5.0 product.
See API(5FEA) for details.
POSIX_SOCKETS
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.
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 mumber of TCP ; see getprotoent(3POSIX) .
The optval and optlen parameters 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 supplied as 0.
The optname parameter and any options specified 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 (7P).
Most socket-level options take 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. The SO_LINGER option uses a
struct
linger
parameter, defined in <
sys/socket.h
>, which specifies the desired state of the option
and the linger interval (see below).
SO_SNDTIMEO
and
SO_RCVTIMEO
use a
struct
timeval
parameter, defined in
<sys/time.h>
.
The following options are recognized at the socket level. Except as noted, each may be examined using getsockopt and set using setsockopt .
toggle recording of debugging information.
toggle local address reuse.
enable duplicate address and port bindings.
toggle keep connections alive.
toggle routing bypass for outgoing messages.
linger on close if data present.
toggle permission to transmit broadcast messages.
toggle reception of out-of-band data in band.
set buffer size for output.
set buffer size for input.
set minimum count for output.
set minimum count for input.
set timeout value for output.
set timout value for input.
get the type of the socket (get only).
get and clear error on the socket (get only).
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 (2POSIX) call should allow reuse of local addresses. The SO_REUSEPORT option allows completely duplicate bindings by multiple processes if they all set SO_REUSEPORT before binding the port. This option permits multiple instances of a program, each to receive multicast or broadcast datagrams destined for the bound port. The SO_KEEPALIVE option enables the periodic transmission of messages on a connected socket. Should the connected party fail t o respond to these messages, the connection is considered broken. 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 (2POSIX) is performed. If the socket confirms reliable delivery of data and SO_LINGER is set, the system will block the process on the close (2POSIX) attempt until it is able to transmit the data or until 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 (2POSIX) is issued, the system will process the close in a manner that allows the process to continue as quickly as possible.
The SO_BROADCAST option 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 to
recv
(2POSIX)
or
read
(2POSIX)
calls without the MSG_OOB flag. The SO_SNDBUF and SO_RCVBUF options allow
you to 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 system
places an absolute limit on these values, which can be accessed through the
sysctl(1M)
MIB
variable,
kern.maxsockbuf
.
SO_SNDLOWAT is an option to set the minimum count for output operations. Most output operations process all of the data supplied by the call, delivering data to the protocol for transmission and blocking as necessary for flow control. Nonblocking output operations will process as much data as permitted, subject to flow control without blocking, but will process no data if flow control does not allow the smaller of either the low water mark value or the entire request to be processed. A select(2POSIX) operation testing the ability to write to a socket will return true only if the low water mark amount could be processed. The default value for SO_SNDLOWAT is set to a convenient size for network efficiency, often 1024.
SO_RCVLOWAT is an option to set the minimum count for input operations. In general, receive calls will block until any (non-zero) amount of data is received, then return with the smaller of the amounts available or the amount requested. The default value for SO_RCVLOWAT is 1. If SO_RCVLOWAT is set to a larger value, blocking receive calls normally wait until they have received the smaller of either the low water mark values or the requested amount. Receive calls may still return less than the low water mark if an error occurs, a signal is caught, or the type of data next in the receive queue is different from that which was returned.
SO_SNDTIMEO is an option to set a timeout value for output operations. It accepts a struct timeval parameter with the number of seconds and microseconds used to limit waits for output operations to complete. If a send operation has blocked for this amount of time, it returns with a partial count or with the error EWOULDBLOCK if no data were sent. In the current implementation, this timer is restarted each time additional data are delivered to the protocol, implying that the limit applies to output portions ranging in size from the low water mark to the high water mark for output.
SO_RCVTIMEO is an option to set a timeout value for input operations. It accepts a struct timeval parameter with the number of seconds and microseconds used to limit waits for input operations to complete. In the current implementation, this timer is restarted each time additional data are received by the protocol, and thus the limit is in effect an inactivity timer. If a receive operation has been blocked for this much time without receiving additional data, it returns with a short count or with the error EWOULDBLOCK if no data were received.
Finally, SO_TYPE and SO_ERROR are options used only with setsockopt . The SO_TYPE option returns the type of the socket, such as 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 any other asynchronous errors.
Upon successful completion, getsockopt and setsockopt return 0; otherwise they return -1 and set errno to indicate one of the following error conditions:
The s argument is not a valid descriptor.
The optval argument is an invalid pointer.
The s argument is a file, not a socket.
The option is unknown at the level indicated.
See attributes(5) for descriptions of the following attributes:
ATTRIBUTE TYPE | ATTRIBUTE VALUE |
---|---|
Interface Stability | Evolving |
MT-level | MT-safe |
sysctl(1M) , bind(2POSIX) , close(2POSIX) , ioctl(2POSIX) , read(2POSIX) , recv(2POSIX) , socket(2POSIX) , getprotoent(3POSIX) , protocols(4CC)
NAME | SYNOPSIS | API RESTRICTIONS | FEATURES | DESCRIPTION | RETURN VALUES | ATTRIBUTES | SEE ALSO