# define IPC_CREAT 0001000 /* create entry if key doesn't exist */
# define IPC_EXCL 0002000 /* fail if key exists */
# define IPC_NOWAIT 0004000 /* error if request must wait */
/* Keys. */
# define IPC_PRIVATE (key_t)0 /* private key */
/* Control Commands. */
# define IPC_RMID 0 /* remove identifier */
# define IPC_SET 1 /* set options */
# define IPC_STAT 2 /* get options */
/* Common IPC Definitions. */
/* Mode bits. */
# define IPC_ALLOC 0100000 /* entry currently allocated */
# define IPC_LOCKED 0040000 /* structure is locked */
# define IPC_WANTED 0004000 /* process waiting for lock *