network: 0.849
device: 0.837
instruction: 0.831
semantic: 0.752
socket: 0.658
other: 0.653
mistranslation: 0.645
graphic: 0.613
boot: 0.572
vnc: 0.474
assembly: 0.330
KVM: 0.127

libvirt cannot hot insert interfaces to qemu

When attempting to hot insert an interface using Ubuntu 16.04.1, I get the following
$ virsh attach-interface --domain gluster1 --type direct \
>         --source test0 --model virtio \
>         --mac 2a:b6:b0:dc:c7:c4 --config --live
error: Failed to attach interface
error: internal error: unable to execute QEMU command 'getfd': No file descriptor supplied via SCM_RIGHTS

test0 exists:
$ ip link show test0
35: test0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000
    link/ether aa:8c:65:2e:79:61 brd ff:ff:ff:ff:ff:ff

Just in case I did it wrong with direct, I did network
$ virsh net-list
 Name                 State      Autostart     Persistent
----------------------------------------------------------
 default              active     yes           yes
 mgmtnet0             active     yes           yes

$ virsh attach-interface --domain gluster1 --type network \
>         --source default --model virtio \
>         --mac 2a:b6:b0:dc:c7:c4 --config --live
error: Failed to attach interface
error: internal error: unable to execute QEMU command 'getfd': No file descriptor supplied via SCM_RIGHTS


This seems to be an old bug, but is still present.  Other relevant information:
$ qemu-system-x86_64 --version
QEMU emulator version 2.5.0 (Debian 1:2.5+dfsg-5ubuntu10.5), Copyright (c) 2003-2008 Fabrice Bellard
$ virsh -v
1.3.1

This looks like a libvirt bug at a first glance. Have you tried to report it to the libvirt project? (See https://libvirt.org/bugs.html ) ... also, can you re-create the bug with the very latest upstream version of libvirt and qemu, or does it only occur with an (older?) version of Ubuntu?

That seems to be the Libvirt of Ubuntu in Xenial.

In the past similar issues were uncommon configs or changed behavior on updates that triggered apparmor or SELinux protection.

=> https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1747442
=> https://bugzilla.redhat.com/show_bug.cgi?id=731243

It could as well be some variant of bug 1677398.

If you are still affected by this, could you check:
1. if it also happens on newer libvirt versions e.g. do a trial run in the most recent Ubuntu
2. if it does could you check dmesg in your setup for related apparmor denials?