man/io_uring_enter.2: note that cqe->flags is indeed used
@@ -983,7 +983,11 @@ is copied from the field of the same name in the submission queue
entry. The primary use case is to store data that the application
will need to access upon completion of this particular I/O. The
.I flags
-is reserved for future use.
+is used for certain commands, like
+.B IORING_OP_POLL_ADD
+or in conjunction with
+.B IOSQE_BUFFER_SELECT
+, see those entries.
.I res
is the operation-specific result, but io_uring-specific errors
(e.g. flags or opcode invalid) are returned through this field.
