Comment 0 for bug 1684481

Setup:
- Xenial host
- lxd guests with Trusty, Xenial, ...
- add a LXD profile to allow kvm [3] (inspired by stgraber)
- spawn KVM guests in the LXD guests using the different distro release versions
- guests are based on the uvtool default template which has a serial console [4]

Issue:
- guest starting with serial device gets blocked by apparmor and killed on creation
- This affects at least ppc64el and x86 (s390x has no serial concept that would match)
- This appeared in our usual checks on -proposed releases so maybe we can/should stop something?
  Last good was "Apr 5, 2017 10:40:50 AM" first bad one "Apr 8, 2017 5:11:22 AM"

Background:
We use this setup for a while and it was working without a change on our end.
Also the fact that it still works in the Trusty LXD makes it somewhat suspicious.
Therefore I'd assume an SRUed change in LXD/Kernel/Apparmor might be the reason and open this bug to get your opinion on it.

You can look into [1] and search for uvt-kvm create in it.

Deny in dmesg:
[652759.606218] audit: type=1400 audit(1492671353.134:4520): apparmor="DENIED" operation="open" namespace="root//lxd-testkvm-xenial-from_<var-lib-lxd>" profile="libvirt-668e21f1-fa55-4a30-b325-0ed5cfd55e5b" name="/dev/pts/ptmx" pid=27162 comm="qemu-system-ppc" requested_mask="wr" denied_mask="wr" fsuid=0 ouid=0

Qemu-log:
2017-04-20T06:55:53.139450Z qemu-system-ppc64: -chardev pty,id=charserial0: Failed to create PTY: No such file or directory

There was a similar issue on qmeu namespacing (which we don't use on any of these releases) [2].
While we surely don't have the "same" issue the debugging on the namespacing might be worth as it could be related.

Workaround for now:
- drop serial section from guest xml

[1]: https://jenkins.ubuntu.com/server/view/Virt/job/virt-migration-cross-release-amd64/78/consoleFull
[2]: https://bugzilla.redhat.com/show_bug.cgi?id=1421036
[3]: https://git.launchpad.net/~ubuntu-server/ubuntu/+source/qemu-migration-test/tree/kvm_profile.yaml
[4]: https://libvirt.org/formatdomain.html#elementsCharPTY