[libvirt PATCH 1/2] network: don't wait for IPv6 DAD completion when starting a network

Laine Stump laine at redhat.com
Fri Sep 4 18:01:14 UTC 2020

0f7436ca54 added code during virtual network startup to wait for DAD
(Duplicate Address Detection) to complete if there were any IPv6
addresses on the network. This wait was needed because (according to
the commit log) "created problems when [the "dummy" tap device] is set
to IFF_DOWN prior to DAD completing".

That commit in turn referenced commit db488c7917, which had added the
code to set the dummy tap device IFF_DOWN, commenting "DAD has
happened (dnsmasq waits for it)", and in its commit message pointed
out that if we just got rid of the dummy tap device this wouldn't be

Now that the dummy tap device has indeed been removed (commit
ee6c936fbb), there is no longer any need to set it IFF_DOWN, and thus
nothing requiring us to wait for DAD to complete. At any rate, with
the dummy tap device removed, leaving nothing else on the bridge when
it is first started, DAD never completes, leading to failure to start
any IPv6 network.

So, yes, this patch removes the wait for DAD completion, and IPv6
networks can once again start, and their associated dnsmasq process
starts successfully (this is the problem that the DAD wait was
originally intended to fix)

Signed-off-by: Laine Stump <laine at redhat.com>
 src/network/bridge_driver.c | 32 --------------------------------
 1 file changed, 32 deletions(-)

diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c
index 5c00befc16..87d7acab06 100644
--- a/src/network/bridge_driver.c
+++ b/src/network/bridge_driver.c
@@ -2286,32 +2286,6 @@ networkAddRouteToBridge(virNetworkObjPtr obj,
     return 0;
-static int
-networkWaitDadFinish(virNetworkObjPtr obj)
-    virNetworkDefPtr def = virNetworkObjGetDef(obj);
-    virNetworkIPDefPtr ipdef;
-    g_autofree virSocketAddrPtr *addrs = NULL;
-    virSocketAddrPtr addr = NULL;
-    size_t naddrs = 0;
-    int ret = -1;
-    VIR_DEBUG("Begin waiting for IPv6 DAD on network %s", def->name);
-    while ((ipdef = virNetworkDefGetIPByIndex(def, AF_INET6, naddrs))) {
-        addr = &ipdef->address;
-        if (VIR_APPEND_ELEMENT_COPY(addrs, naddrs, addr) < 0)
-            goto cleanup;
-    }
-    ret = (naddrs == 0) ? 0 : virNetDevIPWaitDadFinish(addrs, naddrs);
- cleanup:
-    VIR_DEBUG("Finished waiting for IPv6 DAD on network %s with status %d",
-              def->name, ret);
-    return ret;
 static int
 networkStartNetworkVirtual(virNetworkDriverStatePtr driver,
@@ -2444,12 +2418,6 @@ networkStartNetworkVirtual(virNetworkDriverStatePtr driver,
     if (v6present && networkStartRadvd(driver, obj) < 0)
         goto error;
-    /* dnsmasq does not wait for DAD to complete before daemonizing,
-     * so we need to wait for it ourselves.
-     */
-    if (v6present && networkWaitDadFinish(obj) < 0)
-        goto error;
     if (virNetDevBandwidthSet(def->bridge, def->bandwidth, true, true) < 0)
         goto error;

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