On Fri, Feb 24, 2017 at 08:37:51AM -0800, Roberto Cardona wrote: > I'm trying to start a virtual machine by calling qemu-kvm directly but > I am having issues with the vhost file descriptor (vhostfd). > > According to qemu's source code you must pass the file descriptor of > the previously opened vhost_net device so, in order to do this, I am > using a python script with something like this: os.open( > "/dev/vhost-net", os.O_RDWR). Afterwards it passes this to qemu-kvm as > a subprocess. > > I took this off the command that libvirt generates so I know this work > and all kernel modules are enabled. > > Is there any workaround for this so that I can call qemu-kvm directly > without libvirt? > > Error messages: > qemu-kvm: -netdev tap,id=hostnet0,vhost=on,fd=3: TUNGETIFF ioctl() > failed: Inappropriate ioctl for device > qemu-kvm: -netdev tap,id=hostnet1,vhost=on,fd=4: TUNGETIFF ioctl() > failed: Inappropriate ioctl for device > > Network device arguments passed to qemu-kvm (fd 3 and 4 are the fds > that Python opened): > -netdev tap,id=hostnet0,vhost=on,fd=3 3<>/dev/tap5,vhostfd=3 > -device virtio-net > pci,netdev=hostnet0,id=net0,mac=52:54:00:01:cb:a5,bus=pci.0,addr=0x3 > -netdev tap,id=hostnet1,vhost=on,fd=4 4<>/dev/tap24,vhostfd=4 > -device virtio-net > pci,netdev=hostnet1,id=net1,mac=52:50:00:1b:ce:6e,bus=pci.0,addr=0x4 > > Version: > QEMU emulator version 2.6.0 (qemu-kvm-ev-2.6.0-28.el7_3.3.1) File descriptor passing is optional. Libvirt uses it so that QEMU can be launched without root privileges. It's a good idea to follow this practice for production environments or when dealing with untrusted guests. But remember, it's optional and you can skip fd passing if you want. fd=X and vhostfd=Y are supposed to be different device types: * fd=X is a tap-like device (either /dev/tapN or macvtap) * vhostfd=Y is /dev/vhost-net Looks like your code is just opening /dev/tapN and using that fd for both fd=X and vhostfd=Y. This is incorrect and causes the ioctl error. Stefan
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