1QA output created by 114 2Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864 3Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base 4image: TEST_DIR/t.IMGFMT 5file format: IMGFMT 6virtual size: 64M (67108864 bytes) 7cluster_size: 65536 8backing file: TEST_DIR/t.IMGFMT.base 9backing file format: foo 10can't open device TEST_DIR/t.qcow2: Could not open backing file: Unknown driver 'foo' 11no file open, try 'help open' 12read 4096/4096 bytes at offset 0 134 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) 14*** done 15