QA output created by 268
step 1......mkfs.btrfs
wrote 262144/262144 bytes
XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
ERROR: cannot scan /dev/nullb0: Input/output error
ERROR: cannot scan /dev/nullb0: Input/output error
step 2......corrupt file extent
step 3......try to repair
pread: Input/output error