Documentation/trace/ring-buffer-design.rst

437    UPDATE
462 change the pointer to the UPDATE state::
481 "-U->" represents a pointer in the UPDATE state.
492 Note, the flags UPDATE and HEADER are never set at the same time.
599 flag to have the UPDATE flag set. Once this is done, the reader will
755 The write converts the head page pointer to UPDATE::
768 fact that it sees the UPDATE flag instead of a HEADER or NORMAL
782 that converted a pointer from HEAD to UPDATE will convert it back
794 the UPDATE pointer to NORMAL::
820 The write converts the head page pointer to UPDATE::
855 It changes it from HEAD to UPDATE::
880 But now that the third writer did change the HEAD flag to UPDATE it
971 remain in UPDATE and only reset by the outermost writer. This prevents