Hi Aleksi, Thanks for the report. I actually ran into the same situation recently, wanting to set up a PPPoE connection from within a Xen domU, also using openvswitch as bridge.
On 19/03/2024 12:21, Aleksi Suhonen wrote: > Package: src:xen > Version: 4.17.3+10-g091466ba55-1~deb12u1 > Severity: wishlist > > I wasn't sure if this script comes from Debian or Xen or somewhere else, > so I thought it safest to report it here. These scripts/vif-* files are located in tools/hotplug/Linux in the Xen source tree, we ship them as such in the Debian package. So, yes, changes to them should first go upstream. However, it's perfectly fine to have a discussion here, so we can figure out what the right changes should be. > /etc/xen/scripts/vif-bridge handles MTU settings in the vif, but the > otherwise similar /etc/xen/scripts/vif-openvswitch does not. I added it > in, here's the diff-c and the full fixed file is also attached. > > *** vif-openvswitch.orig 2024-03-19 11:53:13.000000000 +0200 > --- vif-openvswitch 2024-03-19 11:56:17.000000000 +0200 > *************** > *** 89,94 **** > --- 89,95 ---- > add|online) > check_tools > setup_virtual_bridge_port $dev > + set_mtu "$bridge" "$dev" "$type_if" > add_to_openvswitch $dev > ;; Ah, interesting. I had some difficulties getting it to work back then. But, when putting the set_mtu line back like this, it also gives me the desired outcome now! My use case is about setting up a PPPoE connection from a Xen domU over vlan 6. I want an mtu of 1500 for the traffic inside the PPPoE connection, so I need mtu 1508 for the connection between the PPPoE client in the domU -> openvswitch in the dom0 -> physical interface -> switchports -> ISP NTU device. For some reason I had troubles to get the vifX.Y interface, as seen inside dom0 set to mtu 1508. It seemed not to have any effect (using ip link set mtu <M> dev <D>), or, openvswitch kept resetting it back to 1500 all the time. When I would use ovs-vsctl set interface <D> mtu_request=<M> instead, it actually sticked. That's what I remember. I just did some more testing, and I cannot really reproduce that situation... :| I can also just use ip link in the dom0 now. Interesting, but good, since it would mean that we can indeed just (re)use that set_mtu function! :) I'm still curious what the problem was when I tried earlier... Maybe anyone else reading this knows more? Are you familiar with the process of sending patches upstream? Otherwise we (Debian Xen team) can assist with that. Regards, Hans
