为什么setsockopt返回EINVAL？

Question

我试图使用setsockopt函数将一个地址添加到接口的多播地址列表中，但是它在EINVAL中失败了。我在内核代码中放置了一些printk，看起来最终在内核packet_setsockopt函数中设置了errno，因为optlen的值小于packet_mreq结构的大小。为了我的生命，我不知道为什么会发生这种事。以下是相关代码：

int addMulticastAddress(int ifindex, unsigned char macaddr[6]) {

    struct packet_mreq mreq;
    int fd;
    int ret = -1;


    if ((fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL))) < 0) {
        return -1;
    }

    memset(&mreq, 0, sizeof(struct packet_mreq));
    mreq.mr_ifindex = ifindex;
    mreq.mr_type = PACKET_MR_MULTICAST;
    memcpy(mreq.mr_address, macaddr, 6);
    mreq.mr_alen = 6;

    if (setsockopt(fd, SOL_PACKET,
                   PACKET_ADD_MEMBERSHIP,
                   &mreq, sizeof(struct packet_mreq) < 0)) {
        virReportSystemError(errno,
                             _("Failed to %s %s %s multicast list for '%s' interface"),
                             add ? "add" : "delete",
                             virMacAddrFormat(macaddr, macstr),
                             add ? "to" : "from", ifname);
        goto cleanup;
    }

    ret = 0;

 cleanup:
     close(fd);
     return ret;
}

Answer 1

你的括号中有一个在错误的地方：

if (setsockopt(fd, SOL_PACKET,
    PACKET_ADD_MEMBERSHIP,
    &mreq, sizeof(struct packet_mreq) < 0)) {

应：

if (setsockopt(fd, SOL_PACKET,
    PACKET_ADD_MEMBERSHIP,
    &mreq, sizeof(struct packet_mreq)) < 0) {