Re: [PATCH 1/4] qemu: prevent unnecessarily failing live interface update

Attempts to use update-device to modify just the link state of a guest interface were failing due to a supposed attempt to modify something in the interface that can't be modified live (even though the only thing that was changing was the link state, which *can* be modified live). It turned out that this failure happened because the guest interface in question was type='network', and the network in question was a 'direct' network that provides each guest interface with one device from a pool of network devices. As a part of qemuDomainChangeNet() we would always allocate a new port from the network driver for the updated interface definition (by way of calling virDomainNetAllocateActualDevice(newdev)), and this new port (ie the ActualNetDef in newdev) would of course be allocated a new host device from the pool (which would of course be different from the one currently in use by the guest interface (in olddev)). Because direct interfaces don't support changing the host device in a live update, this would cause the update to fail. The solution to this is to realize that as long as the interface doesn't get switched to a different network as a part of the update, the network port information (ie the ActualNetDef) will not change as a part of updating the guest interface itself. So for sake of comparison we can just point the newdev at the ActualNetDef of olddev, and then clear out one or the other when we're done (to avoid a double free or, more likely, attempt to reference freed memory). (If, on the other hand, the name of the network has changed, or if the interface type has changed to type='network' from something else, then we *do* need to allocate a new port (actual device) from the network driver (as we used to do in all cases when the new type was 'network'), and also indicate that we'll need to replace olddev in the domain with newdev (because either of these changes is major enough that we shouldn't just try to fix up olddev) Resolves: https://issues.redhat.com/browse/RHEL-7036 Signed-off-by: Laine Stump <laine(a)redhat.com&gt; --- src/qemu/qemu_hotplug.c | 92 +++++++++++++++++++++++++++++++++++------ 1 file changed, 80 insertions(+), 12 deletions(-) diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c index 75b97cf736..a187466c5b 100644 --- a/src/qemu/qemu_hotplug.c +++ b/src/qemu/qemu_hotplug.c @@ -3675,6 +3675,7 @@ qemuDomainChangeNet(virQEMUDriver *driver, virDomainNetDef **devslot = NULL; virDomainNetDef *olddev; virDomainNetType oldType, newType; + bool actualSame = false; bool needReconnect = false; bool needBridgeChange = false; bool needFilterChange = false; @@ -3895,15 +3896,49 @@ qemuDomainChangeNet(virQEMUDriver *driver, * free it if we fail for any reason */ if (newdev->type == VIR_DOMAIN_NET_TYPE_NETWORK) { - if (!(conn = virGetConnectNetwork())) - goto cleanup; - if (virDomainNetAllocateActualDevice(conn, vm->def, newdev) < 0) - goto cleanup; - } + if (olddev->type == VIR_DOMAIN_NET_TYPE_NETWORK + && STREQ(olddev->data.network.name, newdev->data.network.name)) { + /* old and new are type='network', and the network name + * hasn't changed. In this case we *don't* want to get a + * new port ("actual device") from the network because we + * can use the old one (since it hasn't changed). + * + * So instead we just duplicate *the pointer to* the + * actualNetDef from olddev to newdev so that comparisons + * of actualNetDef will show no change. If the update is + * successful, we will clear the actualNetDef pointer from + * olddev before destroying it (or if the update fails, + * then we need to clear the pointer from newdev before + * destroying it) + */ + newdev->data.network.actual = olddev->data.network.actual; + memcpy(newdev->data.network.portid, olddev->data.network.portid, + sizeof(newdev->data.network.portid));

+ actualSame = true; /* old and new actual are pointing to same object */ + } else { + /* either the olddev wasn't type='network', or else the + * name of the network changed. In this case we *do* want + * to get a new port from the new network (because we know + * that it *will* change), and then if the update is + * successful, we will release the port ("actual device") + * in olddev. Or if the update is a failure, we will + * release this new port + */ + if (!(conn = virGetConnectNetwork()) + || virDomainNetAllocateActualDevice(conn, vm->def, newdev) < 0) {

+ goto cleanup; + }