/* recvfd.c * * Receive a file descriptor : */#include "common.h"/* * Receive a file descriptor from the * socket. * * ARGUMENTS: *  s       Socket to receive file *          descriptor on. * * RETURNS: *  >= 0    Received file descriptor *  -1      Failed: See errno */intrecv_fd(int s) {    int z;    struct msghdr msgh;  /* Message header */    struct iovec iov[1];     /* I/O vector */    struct cmsghdr *cmsgp = NULL;    char buf[CMSG_SPACE(sizeof(int))];    char dbuf[80];    /* Small data buffer */    /*     * Initialize structures to zero bytes:     */    memset(&msgh,0,sizeof msgh);    memset(buf,0,sizeof buf);    /*     * No socket addresses are used here:     */    msgh.msg_name = NULL;    msgh.msg_namelen = 0;    /*     * Install our I/O vector :     */    msgh.msg_iov = iov;    msgh.msg_iovlen = 1;    /*     * Initilize I/O vector to read data     * into our dbuf[] array :     */    iov[0].iov_base = dbuf;    iov[0].iov_len = sizeof dbuf;    /*     * Load control data into buf[] :     */    msgh.msg_control = buf;    msgh.msg_controllen = sizeof buf;    /*     * Receive a message :     */    do  {        z = recvmsg(s,&msgh,0);    } while ( z == -1 && errno == EINTR );    if ( z == -1 )        return -1;    /* Failed: see errno */    /*     * Walk the control structure looking for     * a file descriptor :     */    for ( cmsgp = CMSG_FIRSTHDR(&msgh);        cmsgp != NULL;        cmsgp = CMSG_NXTHDR(&msgh,cmsgp) ) {        if ( cmsgp->cmsg_level == SOL_SOCKET        && cmsgp->cmsg_type == SCM_RIGHTS ) {            /*             * File descriptor found :             */            return *(int *) CMSG_DATA(cmsgp);        }    }    /*     * No file descriptor was received:     * If we received 4 bytes, assume we     * received an errno value... then     * set errno from our received data.     */    if ( z == sizeof (int) )        errno = *(int *)dbuf; /* Rcvd errno */    else        errno = ENOENT;    /* Default errno */    return -1; /* Return failure indication */}