[libvirt] Re: [RFC PATCH] Let network bridge MTU to be configured on XML

Mark McLoughlin markmc at redhat.com
Thu Dec 4 17:54:24 UTC 2008

On Thu, 2008-12-04 at 15:42 -0200, Eduardo Habkost wrote:

> This implementation has an issue: it works when trying to set the MTU
> below 1500, but the kernel bridge code doesn't let us to set the bridge
> MTU above 1500 if there is no interface attached to the bridge yet. To
> allow setting the bridge MTU higher than 1500, we need to save the
> configured value somewhere and set it only when attaching tap interface
> to it.

Wait, that doesn't make much sense.

1) create bridge, can't set the MTU to greater than 1500

2) add tap device, set tap MTU to that of the bridge, i.e. 1500

3) now setting the bridge MTU to >1500 won't work because it's greater 
   that the MTU of one of the constituents

Sounds to me like it's just a kernel bug - br_change_mtu() should allow
an MTU of >ETH_DATA_LEN if the list is empty.


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