Pointer to the length of data passed to or returned
from the FSD.
Input
Pointer to the length, in bytes, of the data
passed to the file-system driver in pData
Output
Pointer to the length, in bytes, of the data returned
by the file-system driver in pData. If this function returns ERROR_BUFFER_OVERFLOW,
pcbData points to the size of the buffer required to hold the data
returned by the file-system driver.