libc/ipc: add ftok(3) support

https://man.openbsd.org/ftok.3

Signed-off-by: chao.an <anchao@xiaomi.com>

include/sys/ipc.h

@@ -88,7 +88,29 @@ struct ipc_perm
  * Public Function Prototypes
  ****************************************************************************/
 
-key_t ftok(FAR const char *path, int id);
+/****************************************************************************
+ * Name: ftok
+ *
+ * Description:
+ *   Convert a pathname and a project identifier to a System V IPC key.
+ *   The ftok() function uses the identity of the file named by the given
+ *   pathname (which must refer to an existing, accessible file) and the
+ *   least significant 8 bits of proj_id (which must be nonzero) to
+ *   generate a key_t type System V IPC key, suitable for use with
+ *   msgget(2), semget(2), or shmget(2).
+ *
+ * Input Parameters:
+ *   pathname - identity of the file name
+ *   proj_id  - The value that uniquely project identifies.
+ *
+ * Returned Value:
+ *   On success, the generated key_t value is returned.
+ *   On failure -1 is returned, with errno indicating the error as for the
+ *   stat(2) system call.
+ *
+ ****************************************************************************/
+
+key_t ftok(FAR const char *pathname, int proj_id);
 
 #undef EXTERN
 #if defined(__cplusplus)

include/sys/types.h

@@ -158,7 +158,7 @@ typedef int          id_t;
  * semaphores. A key is simply an integer of type key_t
  */
 
-typedef int16_t      key_t;
+typedef int32_t      key_t;
 
 /* Signed integral type of the result of subtracting two pointers */