[libvirt] Virtual disk size associated with a Domain

Hello, Is there any way to fetch the size of all the virtual disks associated with a Domain?? I could not find one in the libvirt API., I tried using 'virStorageVol' and 'virStoragePool', but they returned null objects. Also I fetched 'virDomainBlockStats', but did not understand the information returned. i.e. 'rd_bytes' and 'wr_bytes'. Can we use this info for calculating the disk sizes? Any method for finding this is welcome. using virt or xm or virsh command line tools also. Also, What does the size of the "img" file for a Domain represent? Is it the disc size? Please help. Thanks and Regards Sagar Barve