fdb_add_hole
fdb_add_hole(fdbp, offset1 - offset, nbytes);
fdb_add_hole(fdbp, uoff - offset,
fdb_add_hole(fdbp,
fdb_add_hole(fdbp, uoff - offset,
extern void fdb_add_hole(fdbuffer_t *fdbuf, u_offset_t off, size_t len);