Surprise subsystem has the right to call fc_identify() to validate
whether such filesystem already exists on the disk. This function
shouldn't do full filesystem check (fsck), only basic sanity checks
should be done (superblock identification, basic partition size
check,...). This function MUST use only supplied handle pt_fh and
llseek(2)/read(2) functions, no bread()/bwrite() is
available in such time. If fc_identify() left as NULL, we don't
support any type of identification and as such Surprise assumes this
filesystem type in fallback style. Please try VERY HARD to implement
fc_identify(), use NULL only as the last resort.
First used call is always fs_getparlist, if any global
initialization of filesystem specific data structures is neccessary it
should be done here (only during the first run, of course).
fc_check() must not be NULL for exported filesystems, it checks if
filesystem with specified parameters can be created