Description of problem:
When create a volume in virt-manager, format as cow, allocate 10M, but after finish creating,  the size display as 0M in the vol list.

Version-Release number of selected component (if applicable):
# uname -a
Linux dhcp-4-216 2.6.18-256.el5xen #1 SMP Thu Apr 7 20:09:34 EDT 2011 x86_64 x86_64 x86_64 GNU/Linux
xen-3.0.3-127.el5
libvirt-0.8.2-19.el5
virt-manager-0.6.1-14.el5

How reproducible:
Always

Steps to Reproduce:
1. In dir pool, Click New Volume, input the vol-name, and Format as Cow, Max capacity as 10M, Allocation as 10M, Then finish
2. Check the newly created vol in the volumes list
  
Actual results:
The size display as 0M

# qemu-img info /var/lib/libvirt/dir/a1.img
image: /var/lib/libvirt/dir/a1.img
file format: cow
virtual size: 10M (10485760 bytes)
disk size: 8.0K

# du -s -B1 /var/lib/libvirt/dir/a1.img 
8192	/var/lib/libvirt/dir/a1.img


Expected results:
The size should display as virtual size,which is 10M

Additional info:
For qcow2, qcow, raw type, they all display the virtual size as Size value, not the disk size. I think they should keep consistent.