io_uring_enter.2: add sendzc -EOPNOTSUPP note
Link:
@@ -1098,8 +1098,11 @@ Available since 5.19.
Issue the zerocopy equivalent of a
.BR send(2)
system call. Similar to IORING_OP_SEND, but tries to avoid making intermediate
-copies of data. Zerocopy execution is not guaranteed and it may fall back to
-copying.
+copies of data. Zerocopy execution is not guaranteed and may fall back to
+copying. The request may also fail with
+.B -EOPNOTSUPP ,
+when a protocol doesn't support zerocopy, in which case users are recommended
+to use copying sends instead.
The
.I flags
