[libvirt] [PATCH 1/2] network: added waiting for DAD to finish for bridge address.

[Dmitry Guryanov]

On 07/31/2015 07:35 PM, Maxim Perevedentsev wrote:
> This is a fix for commit db488c79173b240459c7754f38c3c6af9b432970
> dnsmasq main process exits without waiting for DAD, this is dnsmasq
> daemon's task. So we periodically poll the kernel using netlink and
> check whether there are any IPv6 addresses assigned to bridge
> which have 'tentative' state. After DAD is finished, execution continues.
> I guess that is what dnsmasq was assumed to do.

There are some comments on style, but unfortunately I'm not very 
confident in this part of libvirt, so it would be great if someone else 
reviewed these patches.

> ---
>   src/network/bridge_driver.c | 109 +++++++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 108 insertions(+), 1 deletion(-)
>
> diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c
> index 3d6721b..6a7a505 100644
> --- a/src/network/bridge_driver.c
> +++ b/src/network/bridge_driver.c
> @@ -2025,6 +2025,107 @@ networkAddRouteToBridge(virNetworkObjPtr network,
>       return 0;
>   }
>
> +/* return whether DAD is in progress */
Could you, please, specify, which value mean 'DAD is in progress', it's 
unclear from the comment?
> +static int
> +networkParseDadStatus(struct nlmsghdr *nlh, int len,
> +                      virNetworkObjPtr network)
> +{
> +    struct ifaddrmsg *ifaddrmsg_ptr;
> +    unsigned int ifaddrmsg_len;
> +    struct rtattr *rtattr_ptr;
> +    size_t i;
> +    virNetworkIpDefPtr ipdef;
> +    unsigned char prefix;
> +    struct in6_addr *addr;
> +    for (; NLMSG_OK(nlh, len); nlh = NLMSG_NEXT(nlh, len)) {
> +        if (NLMSG_PAYLOAD(nlh, 0) < sizeof(struct ifaddrmsg))
> +            // Message without payload is the last one.

Please, change comments to C89-style, /* */.
Also add braces, libvirt's coding style requires putting braces around 
multi-line
body even if it's a single line of code with a comment.

> +            break;
> +
> +        ifaddrmsg_ptr = (struct ifaddrmsg *)NLMSG_DATA(nlh);
> +        if (!(ifaddrmsg_ptr->ifa_flags & IFA_F_TENTATIVE))
> +            // Not tentative: we are not interested in this entry.
> +            continue;

The same, braces and comment.

> +
> +        ifaddrmsg_len = IFA_PAYLOAD(nlh);
> +        rtattr_ptr = (struct rtattr *) IFA_RTA(ifaddrmsg_ptr);
> +        for (; RTA_OK(rtattr_ptr, ifaddrmsg_len);
> +            rtattr_ptr = RTA_NEXT(rtattr_ptr, ifaddrmsg_len)) {
> +            if (RTA_PAYLOAD(rtattr_ptr) != sizeof(struct in6_addr))
> +                // No address: ignore.
> +                continue;
> +
Braces and comment, also please, fix all such things in code below.

> +            // We check only known addresses.
> +            for (i = 0;
> +                 (ipdef = virNetworkDefGetIpByIndex(network->def, AF_INET6, i));
> +                 i++) {
> +
> +                prefix = virNetworkIpDefPrefix(ipdef);
> +                addr = &ipdef->address.data.inet6.sin6_addr;
> +
> +                if (prefix == ifaddrmsg_ptr->ifa_prefixlen &&
> +                    !memcmp(addr, RTA_DATA(rtattr_ptr),
> +                            sizeof(struct in6_addr)))
> +                    // We found matching tentative address.
> +                    return 1;
> +            }
> +        }
> +    }
> +    return 0;
> +}
> +
> +/* return after DAD finishes for all known IPv6 addresses or an error */
> +static int
> +networkWaitDadFinish(virNetworkObjPtr network)

I'd put this function to src/util/virnetlink.c

> +{
> +    struct nl_msg *nlmsg = NULL;
> +    struct ifaddrmsg ifa;
> +    struct nlmsghdr *resp = NULL;
> +    unsigned int recvbuflen;
> +    int ret = -1, dad = 1;
> +
> +    if (!(nlmsg = nlmsg_alloc_simple(RTM_GETADDR,
> +                    NLM_F_REQUEST | NLM_F_DUMP))) {

style:

if (!(nlmsg = nlmsg_alloc_simple(RTM_GETADDR,
                                  NLM_F_REQUEST | NLM_F_DUMP))) {


> +        virReportOOMError();
> +        return -1;
> +    }
> +
> +    memset(&ifa, 0, sizeof(ifa));
> +    // DAD is for IPv6 adresses only.
> +    ifa.ifa_family = AF_INET6;
> +    if (nlmsg_append(nlmsg, &ifa, sizeof(ifa), NLMSG_ALIGNTO) < 0) {
> +        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> +                   _("allocated netlink buffer is too small"));
please, align second line to the brace

> +        goto cleanup;
> +    }
> +
> +    // Periodically query netlink until DAD finishes on all known addresses.
> +    while (dad) {
> +        if (virNetlinkCommand(nlmsg, &resp, &recvbuflen, 0, 0,
> +                              NETLINK_ROUTE, 0) < 0)
> +            goto cleanup;
> +
> +        if (virNetlinkGetErrorCode(resp, recvbuflen) < 0) {
> +            virReportError(VIR_ERR_SYSTEM_ERROR, "%s",
> +                    _("error reading DAD state information"));
the same

> +            goto cleanup;
> +        }
> +
> +        //Parse response.
> +        dad = networkParseDadStatus(resp, recvbuflen, network);
> +        if (dad)
> +            usleep(1000 * 10);
What if an interface will remain in transient state forever?

> +
> +        VIR_FREE(resp);
> +    }
> +    ret = 0;
> +
> + cleanup:
> +    VIR_FREE(resp);
> +    nlmsg_free(nlmsg);
> +    return ret;
> +}
> +
>   static int
>   networkStartNetworkVirtual(virNetworkDriverStatePtr driver,
>                              virNetworkObjPtr network)
> @@ -2159,7 +2260,13 @@ networkStartNetworkVirtual(virNetworkDriverStatePtr driver,
>       if (v6present && networkStartRadvd(driver, network) < 0)
>           goto err4;
>
> -    /* DAD has happened (dnsmasq waits for it), dnsmasq is now bound to the
> +    /* dnsmasq main process does not wait for DAD to complete,
> +     * so we need to wait for it ourselves.
> +     */
> +    if (v6present && networkWaitDadFinish(network) < 0)
> +        goto err4;
> +
> +    /* DAD has happened, dnsmasq is now bound to the
>        * bridge's IPv6 address, so we can now set the dummy tun down.
>        */
>       if (tapfd >= 0) {
> --
> Sincerely,
> Maxim Perevedentsev
>
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