Originální popis anglicky:
getsockopt - get the socket options
Návod, kniha: POSIX Programmer's Manual
#include <sys/socket.h>
int getsockopt(int
socket, int
level, int
option_name,
void *restrict
option_value , socklen_t *restrict
option_len );
The
getsockopt() function manipulates options associated with a socket.
The
getsockopt() function shall retrieve the value for the option
specified by the
option_name argument for the socket specified by the
socket argument. If the size of the option value is greater than
option_len, the value stored in the object pointed to by the
option_value argument shall be silently truncated. Otherwise, the
object pointed to by the
option_len argument shall be modified to
indicate the actual length of the value.
The
level argument specifies the protocol level at which the option
resides. To retrieve options at the socket level, specify the
level
argument as SOL_SOCKET. To retrieve options at other levels, supply the
appropriate level identifier for the protocol controlling the option. For
example, to indicate that an option is interpreted by the TCP (Transmission
Control Protocol), set
level to IPPROTO_TCP as defined in the
<netinet/in.h> header.
The socket in use may require the process to have appropriate privileges to use
the
getsockopt() function.
The
option_name argument specifies a single option to be retrieved. It
can be one of the following values defined in
<sys/socket.h>:
- SO_DEBUG
- Reports whether debugging information is being recorded.
This option shall store an int value. This is a Boolean
option.
- SO_ACCEPTCONN
- Reports whether socket listening is enabled. This option
shall store an int value. This is a Boolean option.
- SO_BROADCAST
- Reports whether transmission of broadcast messages is
supported, if this is supported by the protocol. This option shall store
an int value. This is a Boolean option.
- SO_REUSEADDR
- Reports whether the rules used in validating addresses
supplied to bind() should allow reuse of local addresses, if this
is supported by the protocol. This option shall store an int value.
This is a Boolean option.
- SO_KEEPALIVE
- Reports whether connections are kept active with periodic
transmission of messages, if this is supported by the protocol.
If the connected socket fails to respond to these messages, the connection shall
be broken and threads writing to that socket shall be notified with a SIGPIPE
signal. This option shall store an
int value. This is a Boolean option.
- SO_LINGER
- Reports whether the socket lingers on close() if
data is present. If SO_LINGER is set, the system blocks the process during
close() until it can transmit the data or until the end of the
interval indicated by the l_linger member, whichever comes first.
If SO_LINGER is not specified, and close() is issued, the system
handles the call in a way that allows the process to continue as quickly
as possible. This option shall store a linger structure.
- SO_OOBINLINE
- Reports whether the socket leaves received out-of-band data
(data marked urgent) inline. This option shall store an int value.
This is a Boolean option.
- SO_SNDBUF
- Reports send buffer size information. This option shall
store an int value.
- SO_RCVBUF
- Reports receive buffer size information. This option shall
store an int value.
- SO_ERROR
- Reports information about error status and clears it. This
option shall store an int value.
- SO_TYPE
- Reports the socket type. This option shall store an
int value. Socket types are described in Socket Types .
- SO_DONTROUTE
- Reports whether outgoing messages bypass the standard
routing facilities. The destination shall be on a directly-connected
network, and messages are directed to the appropriate network interface
according to the destination address. The effect, if any, of this option
depends on what protocol is in use. This option shall store an int
value. This is a Boolean option.
- SO_RCVLOWAT
- Reports the minimum number of bytes to process for socket
input operations. 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 the low water mark value or the requested
amount. (They may 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 returned; for example, out-of-band data.) This option
shall store an int value. Note that not all implementations allow
this option to be retrieved.
- SO_RCVTIMEO
- Reports the timeout value for input operations. This option
shall store a timeval structure with the number of seconds and
microseconds specifying the limit on how long to wait for an input
operation to complete. If a receive operation has blocked for this much
time without receiving additional data, it shall return with a partial
count or errno set to [EAGAIN] or [EWOULDBLOCK] if no data was
received. The default for this option is zero, which indicates that a
receive operation shall not time out. Note that not all implementations
allow this option to be retrieved.
- SO_SNDLOWAT
- Reports the minimum number of bytes to process for socket
output operations. Non-blocking output operations shall process no data if
flow control does not allow the smaller of the send low water mark value
or the entire request to be processed. This option shall store an
int value. Note that not all implementations allow this option to
be retrieved.
- SO_SNDTIMEO
- Reports the timeout value specifying the amount of time
that an output function blocks because flow control prevents data from
being sent. If a send operation has blocked for this time, it shall return
with a partial count or with errno set to [EAGAIN] or [EWOULDBLOCK]
if no data was sent. The default for this option is zero, which indicates
that a send operation shall not time out. The option shall store a
timeval structure. Note that not all implementations allow this
option to be retrieved.
For Boolean options, a zero value indicates that the option is disabled and a
non-zero value indicates that the option is enabled.
Upon successful completion,
getsockopt() shall return 0; otherwise, -1
shall be returned and
errno set to indicate the error.
The
getsockopt() function shall fail if:
- EBADF
- The socket argument is not a valid file
descriptor.
- EINVAL
- The specified option is invalid at the specified socket
level.
- ENOPROTOOPT
-
The option is not supported by the protocol.
- ENOTSOCK
- The socket argument does not refer to a socket.
The
getsockopt() function may fail if:
- EACCES
- The calling process does not have the appropriate
privileges.
- EINVAL
- The socket has been shut down.
- ENOBUFS
- Insufficient resources are available in the system to
complete the function.
The following sections are informative.
None.
None.
None.
None.
bind() ,
close() ,
endprotoent() ,
setsockopt() ,
socket() , the Base Definitions volume of
IEEE Std 1003.1-2001,
<sys/socket.h>,
<netinet/in.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.