BLOCK_SHIFT
u16 size = FIELD_GET(GETBUF_SIZE, message) << BLOCK_SHIFT;
u16 base = FIELD_GET(INITRB_OFFSET, message) << BLOCK_SHIFT;
u16 size = FIELD_GET(INITRB_SIZE, message) << BLOCK_SHIFT;
rptr = ALIGN(rptr + sizeof(*hdr) + size, 1 << BLOCK_SHIFT);
wptr = ALIGN(wptr, 1 << BLOCK_SHIFT);