[Pkg-libvirt-maintainers] Bug#996476: libvirt-daemon: Does not show host veth interfaces as host devices any more

[Martin Pitt]

Package: libvirt-daemon
Version: 7.6.0-1

Since the upgrade of Debian 11 to current testing, libvirt has a regression: It
does not recognize veth devices as "nodedevs" (devices available on the host
and known by libvirt) any more. This breaks assigning them to VMs for
networking or PXE booting.

  # ip link add name eth42 type veth peer name v_eth42
  # virsh nodedev-list --cap net
  net_eth0_52_54_00_12_34_56
  net_lo_00_00_00_00_00_00

→ No trace of eth42 and v_eth42.

This still works fine on Debian 11,  with libvirt 7.0.0-3, systemd 247.3-6, and
kernel 5.10.0-8-cloud-amd64:

  # ip link add name eth42 type veth peer name v_eth42
  # virsh nodedev-list --cap net
  net_eth0_52_54_00_12_34_56
  net_eth42_ba_f8_89_e3_96_41
  net_lo_00_00_00_00_00_00
  net_v_eth42_c2_28_c1_aa_03_0b

I file this against Debian, as none of our other cockpit-tested operating
systems show this regression (Ubuntu 20.04 LTS/21.10, Fedora 34/35, RHEL/CentOS
8/9, etc.). In particular current Fedora 35 has the exact same libvirt version
7.6.0, just a newer systemd (249.4 in Fedora, 247.9 in Debian testing).

I don't think it's related to udev: In both Debian 11 and testing the device
looks exactly alike in `udevadm info --export-db`:

  P: /devices/virtual/net/eth42
  L: 0
  E: DEVPATH=/devices/virtual/net/eth42
  E: SUBSYSTEM=net
  E: INTERFACE=eth42
  E: IFINDEX=6
  E: USEC_INITIALIZED=106226972
  E: ID_MM_CANDIDATE=1
  E: ID_NET_DRIVER=veth
  E: ID_NET_LINK_FILE=/usr/lib/systemd/network/99-default.link
  E: ID_NET_NAME=eth42
  E: NM_UNMANAGED=1
  E: SYSTEMD_ALIAS=/sys/subsystem/net/devices/eth42
  E: TAGS=:systemd:
  E: CURRENT_TAGS=:systemd:

Thanks,

Martin