Description of problem:

virt-resize calculates the size of the block device using the host file
size.  This is completely wrong and it naturally miscalculates things
like qcow2 targets.  It should instead use the guestfs_blockdev_getsize64
API.

Version-Release number of selected component (if applicable):

1.5.12

How reproducible:

Always.

Steps to Reproduce:
1. Create a qcow2 target file.
2. Try to resize with the qcow2 device as the target.
3.
  
Actual results:

Will fail or say the target image is too small.

Expected results:

Should calculate the target size correctly and thus not fail.

Additional info:

Originally reported by Sean Darcy here:
https://www.redhat.com/archives/libguestfs/2010-September/msg00008.html