mcast_join_source_group函数

#include    <errno.h>
#include    <net/if.h>
#include    <sys/socket.h>

#define     SA    struct sockaddr

int mcast_join_source_group(int sockfd, const SA *src, 
    socklen_t srclen,const SA *grp, socklen_t grplen,
    const char *ifname, u_int ifindex)
{
#ifdef MCAST_JOIN_SOURCE_GROUP
    struct group_source_req req;
    if (ifindex > 0) {
        req.gsr_interface = ifindex;
    } else if (ifname != NULL) {
        if ( (req.gsr_interface = if_nametoindex(ifname)) == 0) {
            errno = ENXIO;    /* i/f name not found */
            return(-1);
        }
    } else {
        req.gsr_interface = 0;
    }
    if (grplen > sizeof(req.gsr_group) || 
        srclen > sizeof(req.gsr_source)) {
        errno = EINVAL;
        return -1;
    }
    memcpy(&req.gsr_group, grp, grplen);
    memcpy(&req.gsr_source, src, srclen);
    return (setsockopt(sockfd, family_to_level(grp->sa_family),
            MCAST_JOIN_SOURCE_GROUP, &req, sizeof(req)));
#else
    switch (grp->sa_family) {
#ifdef IP_ADD_SOURCE_MEMBERSHIP
        case AF_INET: {
            struct ip_mreq_source    mreq;
            struct ifreq            ifreq;

            memcpy(&mreq.imr_multiaddr,
               &((struct sockaddr_in *) grp)->sin_addr,
               sizeof(struct in_addr));
            memcpy(&mreq.imr_sourceaddr,
               &((struct sockaddr_in *) src)->sin_addr,
               sizeof(struct in_addr));

            if (ifindex > 0) {
                if (if_indextoname(ifindex, ifreq.ifr_name) == NULL) {
                    errno = ENXIO;    /* i/f index not found */
                    return(-1);
                }
                goto doioctl;
            } else if (ifname != NULL) {
                strncpy(ifreq.ifr_name, ifname, IFNAMSIZ);
                doioctl:
                if (ioctl(sockfd, SIOCGIFADDR, &ifreq) < 0) {
                    return(-1);
                }
                memcpy(&mreq.imr_interface,
                   &((struct sockaddr_in *) &ifreq.ifr_addr)->sin_addr,
                   sizeof(struct in_addr));
            } else {
                mreq.imr_interface.s_addr = htonl(INADDR_ANY);
            }

            return(setsockopt(sockfd, IPPROTO_IP, 
                IP_ADD_SOURCE_MEMBERSHIP,&mreq, sizeof(mreq)));
        }
#endif

#ifdef    IPV6
        /* IPv6 source-specific API is MCAST_JOIN_SOURCE_GROUP */
        case AF_INET6: {}
#endif
        default: {
            errno = EAFNOSUPPORT;
            return(-1);
        }
    }
#endif
}