virt-manager使用cirros创建虚拟机失败，
出现错误代码
Booting from Hard Disk...
Boot failed: not a bootable disk
No bootable device.
解决方案
It appears that virt-manager does not read the hard drive image format of a pre-existing image when creating a new virtual machine and instead chooses the "raw" format. Since virt-manager seems to store it's setting internally, you cannot just edit the ~/.libvirt/qemu/VMNameHere.xml file.
You must export the libvirt vm settings to xml, fix the hard drive image formatting, and import the vm settings back into libvirt.
Export vm settings:
/etc/libvirt/qemu/vm.xml
virsh -c qemu:///session dumpxml VMName > ~/Desktop/VMName.xml
Update the hard drive format in the xml file:
From
<devices>
<emulator>/usr/bin/kvm</emulator>
<disk type='file' device='disk'>
<driver name='qemu' type='raw'/>
<source file='/storage/vmimages/Windows7_x64-01/qcow2-60GB_HDD1.qcow2'/>
<target dev='hda' bus='ide'/>
</disk>
To
<devices>
<emulator>/usr/bin/kvm</emulator>
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'/>
<source file='/storage/vmimages/Windows7_x64-01/qcow2-60GB_HDD1.qcow2'/>
<target dev='hda' bus='ide'/>
</disk>
Import in the fixed xml file:
virsh -c qemu:///session define ~/Desktop/VMName.xml
