On Thu, 14 Dec 2017 00:57:32 +0100
Matthias Schiffer <[email protected]> wrote:
> As you note, there is another occurrence of this calculation in
> vxlan_config_apply():
>
>
> [...]
> if (lowerdev) {
> [...]
> max_mtu = lowerdev->mtu - (use_ipv6 ? VXLAN6_HEADROOM :
> VXLAN_HEADROOM);
> }
>
> if (dev->mtu > max_mtu)
> dev->mtu = max_mtu;
> [...]
>
>
> Unless I'm overlooking something, this should already do the same thing and
> your patch is redundant.
The code above sets max_mtu, and only if dev->mtu exceeds that, the
latter is then clamped.
What my patch does is to actually set dev->mtu to that value, no matter
what's the previous value set by ether_setup() (only on creation, and
only if lowerdev is there), just like the previous behaviour used to be.
Let's consider these two cases, on the existing code:
1. lowerdev->mtu is 1500:
- ether_setup(), called by vxlan_setup(), sets dev->mtu to 1500
- here max_mtu is 1450
- we enter the second if clause above (dev->mtu > max_mtu)
- at the end of vxlan_config_apply(), dev->mtu will be 1450
which is consistent with the previous behaviour.
2. lowerdev->mtu is 9000:
- ether_setup(), called by vxlan_setup(), sets dev->mtu to 1500
- here max_mtu is 8950
- we do not enter the second if clause above (dev->mtu < max_mtu)
- at the end of vxlan_config_apply(), dev->mtu will still be 1500
which is not consistent with the previous behaviour, where it used to
be 8950 instead.
--
Stefano
