Messages in this thread | | | Date | Wed, 23 Feb 2022 17:58:36 +0100 | From | Guillaume Nault <> | Subject | Re: [PATCH net] net: vlan: allow vlan device MTU change follow real device from smaller to bigger |
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On Wed, Feb 23, 2022 at 08:03:42AM -0800, Jakub Kicinski wrote: > On Wed, 23 Feb 2022 12:26:18 +0100 Guillaume Nault wrote: > > Do you mean something like: > > > > ip link set dev eth0 vlan-mtu-policy <policy-name> > > > > that'd affect all existing (and future) vlans of eth0? > > I meant > > ip link set dev vlan0 mtu-policy blah > > but also > > ip link set dev bond0 mtu-policy blah > > and > > ip link set dev macsec0 mtu-policy blah2 > ip link set dev vxlan0 mtu-policy blah2 > > etc.
Unless I'm missing something, that looks very much like what I proposed (these are all ARPHRD_ETHER devices). It's just a bit unclear whether "ip link set dev vlan0 mtu-policy blah" applies to vlan0 or to the vlans that might be stacked on top of it (given your other examples, I assume it's the later).
> > Then I think that for non-ethernet devices, we should reject this > > option and skip it when dumping config. But yes, that's another > > possibility. > > > > I personnaly don't really mind, as long as we keep a clear behaviour. > > > > What I'd really like to avoid is something like: > > - By default it behaves this way. > > - If you modified the MTU it behaves in another way > > - But if you modified the MTU but later restored the > > original MTU, then you're back to the default behaviour > > (or not?), unless the MTU of the upper device was also > > changed meanwhile, in which case ... to be continued ... > > - BTW, you might not be able to tell how the VLAN's MTU is going to > > behave by simply looking at its configuration, because that also > > depends on past configurations. > > - Well, and if your kernel is older than xxx, then you always get the > > default behaviour. > > - ... and we might modify the heuristics again in the future to > > accomodate with situations or use cases we failed to consider. > > To be honest I'm still not clear if this is a real problem. > The patch does not specify what the use case is.
It's probably not a problem as long as we keep sane behaviour by default. Then we can let admins opt in for something more complex or loosely defined.
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