#include "apue.h"#include <sys/socket.h>#if defined(SCM_CREDS)			/* BSD interface */#define CREDSTRUCT		cmsgcred#define SCM_CREDTYPE	SCM_CREDS#elif defined(SCM_CREDENTIALS)	/* Linux interface */#define CREDSTRUCT		ucred#define SCM_CREDTYPE	SCM_CREDENTIALS#else#error passing credentials is unsupported!#endif/* size of control buffer to send/recv one file descriptor */#define RIGHTSLEN	CMSG_LEN(sizeof(int))#define CREDSLEN	CMSG_LEN(sizeof(struct CREDSTRUCT))#define	CONTROLLEN	(RIGHTSLEN + CREDSLEN)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 CREDSTRUCT	*credp;	struct cmsghdr		*cmp;	struct iovec		iov[1];	struct msghdr		msg;	char				buf[2];	/* send_fd/recv_ufd 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;	msg.msg_flags = 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);		msg.msg_control    = cmptr;		msg.msg_controllen = CONTROLLEN;		cmp = cmptr;		cmp->cmsg_level  = SOL_SOCKET;		cmp->cmsg_type   = SCM_RIGHTS;		cmp->cmsg_len    = RIGHTSLEN;		*(int *)CMSG_DATA(cmp) = fd_to_send;	/* the fd to pass */		cmp = CMSG_NXTHDR(&msg, cmp);		cmp->cmsg_level  = SOL_SOCKET;		cmp->cmsg_type   = SCM_CREDTYPE;		cmp->cmsg_len    = CREDSLEN;		credp = (struct CREDSTRUCT *)CMSG_DATA(cmp);#if defined(SCM_CREDENTIALS)		credp->uid = geteuid();		credp->gid = getegid();		credp->pid = getpid();#endif		buf[1] = 0;		/* zero status means OK */	}	buf[0] = 0;			/* null byte flag to recv_ufd() */	if (sendmsg(fd, &msg, 0) != 2)		return(-1);	return(0);}