sendfd - send a file descriptor to a local socket peer
#include <sys/socket.h>
int sendfd(int sockfd, int fd);Send an open file descriptor to a local socket peer connected via sockfd. This is a non-blocking call that will fail if there are too many file descriptors already waiting to be received by the peer.
File descriptors are sent out-of-band and do not affect the regular data streams.
If a file descriptor is successfully sent, sendfd() returns 0. Otherwise, -1 is returned and errno is set to indicate the error.
EBADF: sockfd or fd is not an open file descriptor.ENOTSOCK: sockfd does not refer to a socket.EAFNOSUPPORT: sockfd does not refer to a local domain socket.ENOTCONN: sockfd refers to a socket which is not connected.EINVAL: sockfd does not refer to a connected or accepted socket.EBUSY: There are too many file descriptors already waiting to be received by the peer.sendfd() was first introduced in Plan 9 from User Space.