• Corey Bryant's avatar
    Add support for net bridge · a7c36ee4
    Corey Bryant authored
    The most common use of -net tap is to connect a tap device to a bridge.  This
    requires the use of a script and running qemu as root in order to allocate a
    tap device to pass to the script.
    
    This model is great for portability and flexibility but it's incredibly
    difficult to eliminate the need to run qemu as root.  The only really viable
    mechanism is to use tunctl to create a tap device, attach it to a bridge as
    root, and then hand that tap device to qemu.  The problem with this mechanism
    is that it requires administrator intervention whenever a user wants to create
    a guest.
    
    By essentially writing a helper that implements the most common qemu-ifup
    script that can be safely given cap_net_admin, we can dramatically simplify
    things for non-privileged users.  We still support existing -net tap options
    as a mechanism for advanced users and backwards compatibility.
    
    Currently, this is very Linux centric but there's really no reason why it
    couldn't be extended for other Unixes.
    
    A typical invocation would be similar to one of the following:
    
      qemu linux.img -net bridge -net nic,model=virtio
    
      qemu linux.img -net tap,helper="/usr/local/libexec/qemu-bridge-helper"
                     -net nic,model=virtio
    
      qemu linux.img -netdev bridge,id=hn0
                     -device virtio-net-pci,netdev=hn0,id=nic1
    
      qemu linux.img -netdev tap,helper="/usr/local/libexec/qemu-bridge-helper",id=hn0
                     -device virtio-net-pci,netdev=hn0,id=nic1
    
    The default bridge that we attach to is br0.  The thinking is that a distro
    could preconfigure such an interface to allow out-of-the-box bridged networking.
    
    Alternatively, if a user wants to use a different bridge, a typical invocation
    would be simliar to one of the following:
    
      qemu linux.img -net bridge,br=qemubr0 -net nic,model=virtio
    
      qemu linux.img -net tap,helper="/usr/local/libexec/qemu-bridge-helper --br=qemubr0"
                     -net nic,model=virtio
    
      qemu linux.img -netdev bridge,br=qemubr0,id=hn0
                     -device virtio-net-pci,netdev=hn0,id=nic1
    
      qemu linux.img -netdev tap,helper="/usr/local/libexec/qemu-bridge-helper --br=qemubr0",id=hn0
                     -device virtio-net-pci,netdev=hn0,id=nic1
    Signed-off-by: default avatarAnthony Liguori <aliguori@us.ibm.com>
    Signed-off-by: default avatarRicha Marwaha <rmarwah@linux.vnet.ibm.com>
    Signed-off-by: default avatarCorey Bryant <coreyb@linux.vnet.ibm.com>
    Signed-off-by: default avatarAnthony Liguori <aliguori@us.ibm.com>
    a7c36ee4
tap.h 2.45 KB