7.4 Export filesystem callback sequence

1. fc_getparlist() will be called before any other function,
2. fc_check() will be called to check filesystem specific parameters,
3. fc_getsize() and fc_getsizestruct() will be called to get info about space needed during conversion
4. fc_superblock() if not successful then continues with consecutive calls, called optionally (for same filesystems and locations),
5. fc_mkfs() is called right before any `export'-specific functions that follow below.
6. Any export/writing functions.
7. fc_fsdone() when Surprise is done with export of this filesystem. Any filesystem buffers should be flushed now to the disk. Physical media sync (sync(2)) is not needed to be performed by filesystem module.