On a Monday in 2025, Peter Krempa via Devel wrote:
From: Peter Krempa <pkrempa@redhat.com>
Attempting to set MTU for network types which don't actually use the network device on the host results in a failure. The 'mtu' property is also used e.g. for the 'host_mtu' property of e.g. 'virtio-net-pci' which is applied even in vhost-user mode.
Use the existing switch which selects devices without a network device backend on the host side and skip setting the MTU.
Tested by running 'passt' in vhost-user mode manually:
passt -f --vhost-user -s /tmp/vh.sock
and the following XML:
<interface type="vhostuser"> <mac address="52:54:00:3d:91:97"/> <source type="unix" path="/tmp/vh.sock" mode="client"/> <model type="virtio"/> <mtu size="9999"/> <address type="pci" domain="0x0000" bus="0x00" slot="0x02" function="0x0"/> </interface>
The OS in the guest reports MTU 9999.
Closes: https://gitlab.com/libvirt/libvirt/-/issues/717 Closes: https://gitlab.com/libvirt/libvirt/-/issues/192 Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/qemu/qemu_command.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
Reviewed-by: Ján Tomko <jtomko@redhat.com> Jano