findBlock(BufferTag pageID) returns (Vfd, off_t)
{
   offset = pageID.blockNum * BLOCKSIZE
   fileName = relpath(pageID.rnode)
   if (pageID.forkNum > 0)
      fileName = fileName+"."+pageID.forkNum
   fid = PathNameOpenFIle(fileName, O_READ);
   fSize = VfdCache[fid].fileSize;
   if (offset > fSize) {
      fid = allocate new Vfd for next fork
      offset = offset - fd.fileSize
   }
   return (fd, offset)
}