Description of problem:
The disk is not pre-existing.At the end of the installation wizard, select 'Customize before install', go to the disk details section,click Advanced options and set format as 'qcow2'.Then begin installation. But an error display.

Version-Release number of selected component (if applicable):
# uname -a
Linux dhcp-65-85.nay.redhat.com 2.6.32-99.el6.x86_64 #1 SMP Fri Jan 14 10:46:00
EST 2011 x86_64 x86_64 x86_64 GNU/Linux

virt-manager-0.8.6-1.el6
kernel-2.6.32-99.el6.x86_64
qemu-kvm-0.12.1.2-2.129.el6.x86_64
libvirt-0.8.7-1.el6.x86_64

How reproducible:
Always

Steps to Reproduce:
> - guest creation using qcow2. At the end of the install wizard, select 'Customize
> before install', go to the disk details section,click Advanced options and set
> format as 'qcow2'. but an error display in the installation process.
> Error:
> Unable to complete install: 'internal error Process exited while reading
> console log output: char device redirected to /dev/pts/5
> qemu: could not open disk image /var/lib/libvirt/images/xx.img: Inappropriate
> ioctl for device

  
Actual results:
but an error display in the installation process.
> Error:
> Unable to complete install: 'internal error Process exited while reading
> console log output: char device redirected to /dev/pts/5
> qemu: could not open disk image /var/lib/libvirt/images/xx.img: Inappropriate
> ioctl for device
> 
> # tail -f .virt-manager/virt-manager.log
> ...
>  <devices>
>     <emulator>/usr/libexec/qemu-kvm</emulator>
>     <disk type='file' device='disk'>
>       <driver name='qemu' type='qcow2' cache='none'/>
>       <source file='/var/lib/libvirt/images/xx.img'/>
>       <target dev='vda' bus='virtio'/>
>     </disk>
> ...
> [Wed, 19 Jan 2011 01:53:43 virt-manager 706] DEBUG (error:66) dialog message:
> Unable to complete install: 'internal error Process exited while reading
> console log output: char device redirected to /dev/pts/5
> qemu: could not open disk image /var/lib/libvirt/images/xx.img: Inappropriate
> ioctl for device
> ' : Unable to complete install: 'internal error Process exited while reading
> console log output: char device redirected to /dev/pts/5
> qemu: could not open disk image /var/lib/libvirt/images/xx.img: Inappropriate
> ioctl for device
> '
> Traceback (most recent call last):
>   File "/usr/share/virt-manager/virtManager/asyncjob.py", line 45, in
> cb_wrapper
>     callback(asyncjob, *args, **kwargs)
>   File "/usr/share/virt-manager/virtManager/create.py", line 1622, in
> do_install
>     guest.start_install(False, meter=meter)
>   File "/usr/lib/python2.6/site-packages/virtinst/Guest.py", line 1193, in
> start_install
>     start_xml, final_xml, is_initial)
>   File "/usr/lib/python2.6/site-packages/virtinst/Guest.py", line 1252, in
> _create_guest
>     dom = self.conn.createLinux(start_xml or final_xml, 0)
>   File "/usr/lib64/python2.6/site-packages/libvirt.py", line 1346, in
> createLinux
>     if ret is None:raise libvirtError('virDomainCreateLinux() failed',
> conn=self)
> libvirtError: internal error Process exited while reading console log output:
> char device redirected to /dev/pts/5
> qemu: could not open disk image /var/lib/libvirt/images/xx.img: Inappropriate
> ioctl for device
> 
> And I check the disk img type
> # qemu-img info /var/lib/libvirt/images/xx.img
> image: /var/lib/libvirt/images/xx.img
> file format: raw
> virtual size: 5.0G (5368709120 bytes)
> disk size: 0
> 
> So this disk file format is actually raw,not qcow2 as selected. Then installation display an error.

Expected results:
According to BZ #620878 comment #11, Choosing 'Customize before
install' and changing the format type in the disk details section is not
expected to change the format when creating the new disk image.

So for clear virt-manager UI design,it is better to desensitize the format combobox if the user isn't selecting preexisting storage.

Additional info: