nf_conntrack_helper_register return error

问题

In kernel if I want to restart my conntrack registers with:

nf_conntrack_helper_unregister(&sip[i][j]);
....// redefinition of the sip[i][j] parameters
nf_conntrack_helper_register(&sip[i][j]);

the nf_conntrack_helper_register(&sip[i][j]) will fail

what I m missing?

Here after the detailed source code:

static void __nf_conntrack_sip_fini(void)
{
    int i, j;

    for (i = 0; i < ports_c; i++) {
        for (j = 0; j < ARRAY_SIZE(sip[i]); j++) {
            if (sip[i][j].me == NULL)
                continue;
            nf_conntrack_helper_unregister(&sip[i][j]);
        }
    }
    memset(sip, 0, sizeof(sip));
}

static int __nf_conntrack_sip_init(void)
{
    int i, j, ret;

    if (ports_c == 0)
        ports[ports_c++] = SIP_PORT;

    for (i = 0; i < ports_c; i++) {
        memset(&sip[i], 0, sizeof(sip[i]));

        sip[i][0].tuple.src.l3num = AF_INET;
        sip[i][0].tuple.dst.protonum = IPPROTO_UDP;
        sip[i][0].help = sip_help_udp;
        sip[i][1].tuple.src.l3num = AF_INET;
        sip[i][1].tuple.dst.protonum = IPPROTO_TCP;
        sip[i][1].help = sip_help_tcp;

        sip[i][2].tuple.src.l3num = AF_INET6;
        sip[i][2].tuple.dst.protonum = IPPROTO_UDP;
        sip[i][2].help = sip_help_udp;
        sip[i][3].tuple.src.l3num = AF_INET6;
        sip[i][3].tuple.dst.protonum = IPPROTO_TCP;
        sip[i][3].help = sip_help_tcp;

        for (j = 0; j < ARRAY_SIZE(sip[i]); j++) {
            sip[i][j].data_len = sizeof(struct nf_ct_sip_master);
            sip[i][j].tuple.src.u.udp.port = htons(ports[i]);
            sip[i][j].expect_policy = sip_exp_policy;
            sip[i][j].expect_class_max = SIP_EXPECT_MAX;
            sip[i][j].me = THIS_MODULE;

            if (ports[i] == SIP_PORT)
                sprintf(sip[i][j].name, "sip");
            else
                sprintf(sip[i][j].name, "sip-%u", i);

            pr_debug("port #%u: %u\n", i, ports[i]);

            ret = nf_conntrack_helper_register(&sip[i][j]);
            if (ret) {
                printk(KERN_ERR "nf_ct_sip: failed to register"
                       " helper for pf: %u port: %u i=%d\n",
                       sip[i][j].tuple.src.l3num, ports[i], i);
                __nf_conntrack_sip_fini();
                return ret;
            }
        }
    }
    return 0;
}

static void nf_conntrack_sip_restart(void)
{
    printk("*****Restart SIP Conntrack *****\n");
    __nf_conntrack_sip_fini();
    __nf_conntrack_sip_init();
}

when I trigger nf_conntrack_sip_restart() from user space the __nf_conntrack_sip_init() will return error

By the way the fail does not occur always. Sometimes the register success.

来源：https://stackoverflow.com/questions/36799413/nf-conntrack-helper-register-return-error