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-rw-r--r--bits/sem.h26
1 files changed, 17 insertions, 9 deletions
diff --git a/bits/sem.h b/bits/sem.h
index 8b9f97c62a..cb6657a345 100644
--- a/bits/sem.h
+++ b/bits/sem.h
@@ -1,4 +1,5 @@
-/* Copyright (C) 1995, 1996, 1997 Free Software Foundation, Inc.
+/* Copyright (C) 1995, 1996, 1997, 1998
+ Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -44,11 +45,18 @@ struct semid_ds
unsigned short int sem_nsems; /* number of semaphores in set */
};
-/* Union used for argument for `semctl'. */
-union semun
-{
- int val; /* value for SETVAL */
- struct semid_ds *buf; /* buffer for IPC_STAT & IPC_SET */
- unsigned short int *array; /* array for GETALL & SETALL */
- struct seminfo *__buf; /* buffer for IPC_INFO */
- };
+/* The user should define a union like the following to use it for arguments
+ for `semctl'.
+
+ union semun
+ {
+ int val; <= value for SETVAL
+ struct semid_ds *buf; <= buffer for IPC_STAT & IPC_SET
+ unsigned short int *array; <= array for GETALL & SETALL
+ struct seminfo *__buf; <= buffer for IPC_INFO
+ };
+
+ Previous versions of this file used to define this union but this is
+ incorrect. One can test the macro _SEM_SEMUN_UNDEFINED to see whether
+ one must define the union or not. */
+#define _SEM_SEMUN_UNDEFINED 1