[virt-tools-list] libvirt and virt-manager default Xen blktap driver name for file images, tap vs tap2?

Pasi Kärkkäinen pasik at iki.fi
Sun Jun 9 17:07:16 UTC 2013


Does anyone know where/how to set the default libvirt Xen blktap "driver name" for disk image files?

If I have "blktap" module loaded in dom0 kernel, and I do this:

virt-install -d -n blktaptest01 -r 2048 --vcpus=2 --disk /var/lib/libvirt/images/blktaptest01.img,size=8 --vnc -p -l "http://ftp.funet.fi/pub/mirrors/centos.org/6.4/os/x86_64"

which results in this generated libvirt xml config for the VM:

    <disk type='file' device='disk'>
      <driver name='tap' type='aio'/>
      <source file='/var/lib/libvirt/images/blktaptest01.img'/>
      <target dev='xvda' bus='xen'/>

.. which doesn't seem to work for me with Xen 4.2.2 using xm/xend, and libvirt 0.10.x.

The problem is there's no tapdisk process started in dom0, and the block device cannot be 
initialized or accessed inside the VM. I have the same problem with virt-manager, 
using the "new VM" wizard with disk image files.

The correct "driver name" for libvirt is "tap2", which works for me, 
so I need to manually edit the libvirt xml config to make the VM boot/work:

    <disk type='file' device='disk'>
      <driver name='tap2' type='aio'/>
      <source file='/var/lib/libvirt/images/blktaptest01.img'/>
      <target dev='xvda' bus='xen'/>

This matches xm/xend behaviour with text config files for VMs. 
I need to use tap2 there aswell on the disk = [] line.

Where should I choose/set/patch the default libvirt driver name? Is that in libvirt sources,
or in virt-install/virt-manager ? I tried reading the libvirt "xen" driver source, 
but I couldn't find any "default" setting there.. 


-- Pasi

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