Function vaCreateBuffer2 

pub unsafe extern "C" fn vaCreateBuffer2(
    dpy: VADisplay,
    context: VAContextID,
    type_: Type,
    width: c_uint,
    height: c_uint,
    unit_size: *mut c_uint,
    pitch: *mut c_uint,
    buf_id: *mut VABufferID,
) -> VAStatus

Create a buffer for given width & height get unit_size, pitch, buf_id for 2D buffer for permb qp buffer, it will return unit_size for one MB or LCU and the pitch for alignments can call vaMapBuffer with this Buffer ID to get virtual address. e.g. AVC 1080P encode, 1920x1088, the size in MB is 120x68,but inside driver, maybe it should align with 256, and one byte present one Qp.so, call the function. then get unit_size = 1, pitch = 256. call vaMapBuffer to get the virtual address (pBuf). then read write the memory like 2D. the size is 256x68, application can only use 120x68 pBuf + 256 is the start of next line. different driver implementation maybe return different unit_size and pitch