linux - 为什么 setsockopt 返回 EINVAL？

Question

我正在尝试使用 setsockopt 函数将地址添加到接口(interface)的多播地址列表中，但失败并显示错误号 EINVAL。我在内核代码中放置了一些 printk，看起来 errno 最终是在内核 packet_setsockopt 函数中设置的，因为传递给 optlen 的值小于packet_mreq 结构。对于我的生活，我无法弄清楚为什么会这样。相关代码如下:

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

你的一个括号在错误的地方:

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

应该是:

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