Re: [libvirt] [PATCH v3 22/36] network: remove the virDomainNetBandwidthChangeAllowed callback

On 3/19/19 8:46 AM, Daniel P. Berrangé wrote: > The current qemu driver code for changing bandwidth on a NIC first asks > the network driver if the change is supported, then changes the > bandwidth on the VIF, and then tells the network driver to update the > bandwidth on the bridge. > > This is potentially racing if a parallel API call causes the network > driver to allocate bandwidth on the bridge between the check and the > update phases. > > Change the code to just try to apply the network bridge update > immediately and rollback at the end if something failed. > > Signed-off-by: Daniel P. Berrangé <berrange(a)redhat.com&gt;

> @@ -5391,6 +5334,7 @@ networkBandwidthUpdate(virDomainNetDefPtr iface, > unsigned long long tmp_floor_sum; > virNetDevBandwidthPtr ifaceBand = virDomainNetGetActualBandwidth(iface); > unsigned long long new_rate = 0; > + unsigned long long old_floor, new_floor; > int plug_ret; > int ret = -1; > @@ -5400,7 +5344,21 @@ networkBandwidthUpdate(virDomainNetDefPtr iface, > return -1; > } > - if (!networkBandwidthGenericChecks(iface, newBandwidth)) > + if (virDomainNetGetActualType(iface) != VIR_DOMAIN_NET_TYPE_BRIDGE || > + iface->data.network.actual->data.bridge.brname == NULL) { > + /* This is not an interface that's plugged into a network. > + * We don't care. Thus from our POV bandwidth change is allowed. */ This comment is more confusing than it is helpful. Especially since it's wrong :-)

> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c > index b81c411007..baf188ae40 100644 > --- a/src/qemu/qemu_driver.c > +++ b/src/qemu/qemu_driver.c > @@ -11729,17 +11729,17 @@ qemuDomainSetInterfaceParameters(virDomainPtr dom, > } > if (net->type == VIR_DOMAIN_NET_TYPE_NETWORK && > - !virDomainNetBandwidthChangeAllowed(net, newBandwidth)) > + virDomainNetBandwidthUpdate(net, newBandwidth) < 0) > goto endjob; > if (virNetDevBandwidthSet(net->ifname, newBandwidth, false, > - !virDomainNetTypeSharesHostView(net)) < 0 || > - (net->type == VIR_DOMAIN_NET_TYPE_NETWORK && > - virDomainNetBandwidthUpdate(net, newBandwidth) < 0)) { > + !virDomainNetTypeSharesHostView(net)) < 0) { > ignore_value(virNetDevBandwidthSet(net->ifname, > net->bandwidth, > false, > !virDomainNetTypeSharesHostView(net))); > + ignore_value(virDomainNetBandwidthUpdate(net, > + net->bandwidth)); > goto endjob; > } The new version of the code is calling virDomainNetBandwidthUpdate() and virNetDevBandwidthSet() in reverse order from what it previously did. If either of the functions were to modify newBandwidth's contents, then the results would change. Fortunately it looks like neither of them do that, so I think we're safe.

Reviewed-by: Laine Stump <laine(a)laine.org&gt;