On Mon, 22 Feb 2016 17:29:11 +0800 roy.qing...@gmail.com wrote: > From: Li RongQing <roy.qing...@gmail.com> > > A linux bridge always adopts the smallest MTU of the enslaved devices. > When no device are enslaved, it defaults to a MTU of 1500 and refuses to > use a larger one. This is problematic when using bridges enslaving only > virtual NICs (vnetX) like it's common with KVM guests. > > Steps to reproduce the problem > > 1) sudo ip link add br-test0 type bridge # create an empty bridge > 2) sudo ip link set br-test0 mtu 9000 # attempt to set MTU > 1500 > 3) ip link show dev br-test0 # confirm MTU > > Here, 2) returns "RTNETLINK answers: Invalid argument". One (cumbersome) > way around this is: > > 4) sudo modprobe dummy > 5) sudo ip link set dummy0 mtu 9000 master br-test0 > > Then the bridge's MTU can be changed from anywhere to 9000. > > This is especially annoying for the virtualization case because the > KVM's tap driver will by default adopt the bridge's MTU on startup > making it impossible (without the workaround) to use a large MTU on the > guest VMs. > > https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1399064 > > Signed-off-by: Li RongQing <roy.qing...@gmail.com>
Your change works, but I agree with Hannes. Just allow up to 64 * 1024 like loopback does. And no need for a #define for that it is only in one place.
