[Pkg-libvirt-maintainers] Bug#1008239: libvirt-daemon: wrong MTU on bridge interface created by libvirt

[maxim orlov]

Package: libvirt-daemon-system
Version: 7.0.0-3
Severity: normal
X-Debbugs-Cc: maxx.orlov at gmail.com

After creating virtual network from next XML file:
$ cat test.xml
<network>
  <name>test</name>
  <bridge name='test' stp='off' delay='0'/>
  <mtu size='9000'/>
</network>

$ virsh net-dumpxml test
<network>
  <name>test</name>
  <uuid>6db03fea-1275-4036-aa0c-fa12428631a8</uuid>
  <bridge name='test' stp='off' delay='0'/>
  <mtu size='9000'/>
  <mac address='52:54:00:34:2d:b1'/>
</network>

bridge interface ignore mtu settings 9000 and use default 1500

$ ip link
26: test: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:34:2d:b1 brd ff:ff:ff:ff:ff:ff
                                                  ^^^^

Bug doesn't exist in libvirt 5.0.0-4+deb10u1 (debian 10):
4: test: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 9000 qdisc noqueue state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:23:cf:42 brd ff:ff:ff:ff:ff:ff
5: test-nic: <BROADCAST,MULTICAST> mtu 9000 qdisc pfifo_fast master test state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:23:cf:42 brd ff:ff:ff:ff:ff:ff

in libvirt 6.0.0-0ubuntu8.15 (ubuntu 20.04):
6: test: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 9000 qdisc noqueue state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:97:39:0d brd ff:ff:ff:ff:ff:ff
7: test-nic: <BROADCAST,MULTICAST> mtu 9000 qdisc fq_codel master test state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:97:39:0d brd ff:ff:ff:ff:ff:ff

and in libvirt 8.0.0-1~bpo11+1 (bullseye-backports/main) 
5: test: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 9000 qdisc noqueue state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:3f:42:ee brd ff:ff:ff:ff:ff:ff



-- System Information:
Debian Release: 11.2
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 5.10.0-9-amd64 (SMP w/4 CPU threads)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages libvirt-daemon-system depends on:
ii  adduser                         3.118
ii  debconf [debconf-2.0]           1.5.77
ii  gettext-base                    0.21-4
ii  iptables                        1.8.7-1
ii  libvirt-clients                 7.0.0-3
ii  libvirt-daemon                  7.0.0-3
ii  libvirt-daemon-config-network   7.0.0-3
ii  libvirt-daemon-config-nwfilter  7.0.0-3
ii  libvirt-daemon-system-systemd   7.0.0-3
ii  logrotate                       3.18.0-2
ii  policykit-1                     0.105-31+deb11u1

Versions of packages libvirt-daemon-system recommends:
ii  dmidecode                    3.3-2
ii  dnsmasq-base [dnsmasq-base]  2.85-1
ii  iproute2                     5.10.0-4
ii  mdevctl                      0.81-1
ii  parted                       3.4-1

Versions of packages libvirt-daemon-system suggests:
ii  apparmor    2.13.6-10
pn  auditd      <none>
ii  nfs-common  1:1.3.4-6
pn  open-iscsi  <none>
pn  pm-utils    <none>
pn  radvd       <none>
ii  systemd     247.3-6
pn  systemtap   <none>
pn  zfsutils    <none>

-- Configuration Files:
/etc/libvirt/qemu.conf [Errno 13] Permission denied: '/etc/libvirt/qemu.conf'

-- debconf information excluded