Messages in this thread | | | Date | Tue, 22 Feb 2022 15:28:15 -0800 | From | Jakub Kicinski <> | Subject | Re: [PATCH net] net: vlan: allow vlan device MTU change follow real device from smaller to bigger |
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On Tue, 22 Feb 2022 11:37:33 +0100 Guillaume Nault wrote: > What about an explicit option: > > ip link add link eth1 dev eth1.100 type vlan id 100 follow-parent-mtu > > > Or for something more future proof, an option that can accept several > policies: > > mtu-update <reduce-only,follow,...> > > reduce-only (default): > update vlan's MTU only if the new MTU is smaller than the > current one (current behaviour). > > follow: > always follow the MTU of the parent device. > > Then if anyone wants more complex policies: > > follow-if-not-modified: > follow the MTU of the parent device as long as the VLAN's MTU > was not manually changed. Otherwise only adjust the VLAN's MTU > when the parent's one is set to a smaller value. > > follow-if-not-modified-but-not-quite: > like follow-if-not-modified but revert back to the VLAN's > last manually modified MTU, if any, whenever possible (that is, > when the parent device's MTU is set back to a higher value). > That probably requires the possibility to dump the last > modified MTU, so the administrator can anticipate the > consequences of modifying the parent device. > > yet-another-policy (because people have a lot of imagination): > for example, keep the MTU 4 bytes lower than the parent device, > to account for VLAN overhead. > > Of course feel free to suggest better names and policies :). > > This way, we can keep the current behaviour and avoid unexpected > heuristics that are difficult to explain (and even more difficult for > network admins to figure out on their own).
My $0.02 would be that if we want to make changes that require new uAPI we should do it across uppers.
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