Bug 2138339

Description of problem:
Libvirt since version 6.9.0 (see https://www.libvirt.org/news.html#v6-9-0-2020-11-02) is by default setting "noqueue" qdisc for tap interfaces. So newly created tap device looks in tc like:

qdisc noqueue 8007: dev tap20326cf2-f1 root refcnt 2

When qos and queue is set for such interface in ovs, e.g. with commands like:

ovs-vsctl -- set port tap20326cf2-f1 qos=@newqos -- --id=@newqos create qos type=linux-htb other-config:max-rate=1000000 queues:0=@newqueue -- --id=@newqueue create queue other-config:burst=800000 other-config:max-rate=1000000

OVS fails to create htb qdisc for this interface.

AFAIU ovs, to create proper htb qdisc is doing something like:

tc qdisc add dev tap20326cf2-f1 root handle 1: htb default 100

and this ends up with error like:

Error: NLM_F_REPLACE needed to override.

OVS should first delete existing qdisc with function tc_del_qdisc (https://github.com/openvswitch/ovs/blob/850e639021125c3646effa0eae9e422082ade2ca/lib/netdev-linux.c#L6127) but it not happens. Probably because this function is just trying to delete qdisc with handle "1:0" even if doc says that it's doing equivalent to "tc qdisc del dev <name> root".

Version-Release number of selected component (if applicable):

I checked on:
openvswitch2.15-2.15.0-109.el8fdp.x86_64
and
openvswitch2.17-2.17.0-59.el8fdp.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Spawn VM with libvirt (e.g. using OpenStack)
2. Create qos and queue for tap port in ovs:

ovs-vsctl -- set port tap20326cf2-f1 qos=@newqos -- --id=@newqos create qos type=linux-htb other-config:max-rate=1000000 queues:0=@newqueue -- --id=@newqueue create queue other-config:burst=800000 other-config:max-rate=1000000

or use neutron qos ingress bandwith limit rule to create it automatically by neutron-openvswitch-agent.
3. check if htb qdisc is created for tap port

Actual results:
tap interface still have "noqueue" qdisc configured

Expected results:
tap interface should have "htb" qdisc configured

Additional info: