getsockopt

Synopsis

#include <sys/socket.h>

int getsockopt(int socket, int level, int option_name,
               void *restrict option_value, socklen_t *restrict option_len);

Status

Implemented

Conformance

IEEE Std 1003.1-2017

Description

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 socket-level options defined in <sys/socket.h>.

The default value of the SO_SNDBUF option is implementation-defined. AF_UNIX sockets have no send buffer, as the sent data is stored directly in the receive buffer of the peer socket, so SO_SNDBUF is reported as 0.

Return value

Upon successful completion, getsockopt() shall return 0; otherwise, -1 shall be returned and errno set to indicate the error.

Errors

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 appropriate privileges.

  • EINVAL - The socket has been shut down.

  • ENOBUFS - Insufficient resources are available in the system to complete the function.

POSIX deviations

IEEE Std 1003.1-2017 requires the option value to be silently truncated when its size is greater than option_len. In Phoenix-RTOS, getsockopt() fails with EINVAL in that case, both for AF_UNIX and AF_INET sockets. A truncated value of a multibyte option (for example an int or a struct timeval) can’t be interpreted correctly by the application, so reporting an error is the safer behavior.