Ceph librbd export-diff non-working example

example.py

'''
Issues:  
- Size of written file not identical to size crated by `rbd export-diff` command.
- Total size of extents does not equal diff-size 
'''

offsets = []
extents = []

def iter_cb(offset, length, exists):
    if exists:
        offsets.append(offset)
        extents.append(length)

image.diff_iterate(0, image.size(), None, iter_cb)

with open(os.path.join(BACKUP_DIR, 'test.img'), 'wb') as f:
    for offset, extent in zip(offsets, extents):
        f.write(image.read(offset, extent))
    f.close()