[libvirt] Using -netdev with qemu/kvm rather than old style

[Daniel P. Berrange]

On Wed, Oct 06, 2010 at 12:40:00PM -0600, Pete Ashdown wrote:
> I have 0.8.3 installed and my net devices are still being defined via -net
> rather than -netdev.  I have found that using the latter allows my ethernet to
> properly offload and gives a 35% performance gain.  Looking through the
> libvirt code I find in qemu_conf.c:
> 
>        /* Possible combinations
>         *
>         *  1. Old way:   -net nic,model=e1000,vlan=1 -net tap,vlan=1
>         *  2. Semi-new:  -device e1000,vlan=1        -net tap,vlan=1
>         *  3. Best way:  -netdev type=tap,id=netdev1 -device e1000,id=netdev1 
>         *
>         * NB, no support for -netdev without use of -device
>         */
> 
> How do I convince virsh/libvirt to use #3, the "Best way"?

This option remains disabled until QEMU 0.13 is released. We did briefly
enable it for QEMU 0.12.x, but then discovered that various aspects of it
are broken in that release, in particular hotplug/unplug.

Daniel
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