函数xdes_get_offset

/********************************************************************//**
Returns page offset of the first page in extent described by a descriptor.
@return    offset of the first page in extent */
UNIV_INLINE
ulint
xdes_get_offset(
/*============*/
    xdes_t*    descr)    /*!< in: extent descriptor */
{
    ut_ad(descr);

    return(page_get_page_no(page_align(descr))
           + ((page_offset(descr) - XDES_ARR_OFFSET) / XDES_SIZE)
           * FSP_EXTENT_SIZE);
}