#include "apue.h"#ifdef MACOS#include <sys/uio.h>#endif#include <sys/socket.h>/* size of control buffer to send/recv one file descriptor */#define	CONTROLLEN	CMSG_LEN(sizeof(int))static struct cmsghdr	*cmptr = NULL;	/* malloc'ed first time *//* * Pass a file descriptor to another process. * If fd<0, then -fd is sent back instead as the error status. */intsend_fd(int fd, int fd_to_send){	struct iovec	iov[1];	struct msghdr	msg;	char			buf[2];	/* send_fd()/recv_fd() 2-byte protocol */	iov[0].iov_base = buf;	iov[0].iov_len  = 2;	msg.msg_iov     = iov;	msg.msg_iovlen  = 1;	msg.msg_name    = NULL;	msg.msg_namelen = 0;	if (fd_to_send < 0) {		msg.msg_control    = NULL;		msg.msg_controllen = 0;		buf[1] = -fd_to_send;	/* nonzero status means error */		if (buf[1] == 0)			buf[1] = 1;	/* -256, etc. would screw up protocol */	} else {		if (cmptr == NULL && (cmptr = malloc(CONTROLLEN)) == NULL)			return(-1);		cmptr->cmsg_level  = SOL_SOCKET;		cmptr->cmsg_type   = SCM_RIGHTS;		cmptr->cmsg_len    = CONTROLLEN;		msg.msg_control    = cmptr;		msg.msg_controllen = CONTROLLEN;		*(int *)CMSG_DATA(cmptr) = fd_to_send;		/* the fd to pass */		buf[1] = 0;		/* zero status means OK */	}	buf[0] = 0;			/* null byte flag to recv_fd() */	if (sendmsg(fd, &msg, 0) != 2)		return(-1);	return(0);}