Re: [Xen-devel] [PATCH][qemu-xen] Change tap device mac address to prevent change of bridge's mac

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2010-12-21 at 13:13 +0000, Miroslav Rezanina wrote:
> Qemu tap device is created with random mac address and then add to bridge. 
> Due to linux kernel handlig, bridge change its mac address to tap mac in case 
> tap mac is lower than bridge one. This can lead to short network breakage for 
> dom0 and guests. 
> 
> This patch set tap device mac adress to FE:FF:FF:FF:FF:FF to ensure tap 
> device mac is always higher then bridge one.
> 
> Signed-off-by: Miroslav Rezanina <mrezanin@xxxxxxxxxx>

Thanks. This needed a different fix in xen-unstable.hg because tap
devices are handled by the hotplug scripts and not qemu-ifup there. See
the recent thread "tools/hotplug/Linux: Ensure tap devices receive a
dummy MAC address".

My backport to xen-4.0-testing looked a lot like yours.

Ian.


> 
> Patch:
> --
> diff --git a/i386-dm/qemu-ifup-Linux b/i386-dm/qemu-ifup-Linux
> index bcbee92..c706a10 100644
> --- a/i386-dm/qemu-ifup-Linux
> +++ b/i386-dm/qemu-ifup-Linux
> @@ -33,5 +33,8 @@ then
>     fi
>  fi
>  
> +# We have to change mac address of tap device to not change bridge mac
> +ip link set $1 addr fe:ff:ff:ff:ff:ff
> +
>  ifconfig $1 0.0.0.0 up
>  brctl addif $bridge $1 || true



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