sem_setprotocol: Handle a case of missing proxy for sem_setprotocol. Reorder so that (1) this error is avoided, and (2) >No proxy is needed if priority inheritance is not enabled.

libc/semaphore/Make.defs

@@ -37,6 +37,10 @@
 
 CSRCS += sem_init.c sem_getprotocol.c sem_getvalue.c
 
+ifneq ($(CONFIG_PRIORITY_INHERITANCE),y)
+CSRCS += sem_setprotocol.c
+endif
+
 # Add the semaphore directory to the build
 
 DEPPATH += --dep-path semaphore

libc/semaphore/sem_setprotocol.c

@@ -0,0 +1,114 @@
+/****************************************************************************
+ * libc/semaphore/sem_setprotocol.c
+ *
+ *   Copyright (C) 2016 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <assert.h>
+#include <errno.h>
+
+#include <nuttx/semaphore.h>
+
+#ifndef CONFIG_PRIORITY_INHERITANCE
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Function: sem_setprotocol
+ *
+ * Description:
+ *    Set semaphore protocol attribute.
+ *
+ *    One particularly important use of this furnction is when a semaphore
+ *    is used for inter-task communication like:
+ *
+ *      TASK A                 TASK B
+ *      sem_init(sem, 0, 0);
+ *      sem_wait(sem);
+ *                             sem_post(sem);
+ *      Awakens as holder
+ *
+ *    In this case priority inheritance can interfere with the operation of
+ *    the semaphore.  The problem is that when TASK A is restarted it is a
+ *    holder of the semaphore.  However, it never calls sem_post(sem) so it
+ *    becomes *permanently* a holder of the semaphore and may have its
+ *    priority boosted when any other task tries to acquire the semaphore.
+ *
+ *    The fix is to call sem_setprotocol(SEM_PRIO_NONE) immediately after
+ *    the sem_init() call so that there will be no priority inheritance
+ *    operations on this semaphore.
+ *
+ * Parameters:
+ *    sem      - A pointer to the semaphore whose attributes are to be
+ *               modified
+ *    protocol - The new protocol to use
+ *
+ * Return Value:
+ *   0 if successful.  Otherwise, -1 is returned and the errno value is set
+ *   appropriately.
+ *
+ ****************************************************************************/
+
+int sem_setprotocol(FAR sem_t *sem, int protocol)
+{
+  int errcode;
+
+  DEBUGASSERT(sem != NULL);
+
+  switch (protocol)
+    {
+      case SEM_PRIO_NONE:
+        return OK;
+
+      case SEM_PRIO_INHERIT:
+      case SEM_PRIO_PROTECT:
+        errcode = ENOSYS;
+        break;
+
+      default:
+        errcode = EINVAL;
+        break;
+    }
+
+  set_errno(errcode);
+  return ERROR;
+}
+
+#endif /* !CONFIG_PRIORITY_INHERITANCE */

sched/semaphore/Make.defs

@@ -37,10 +37,10 @@
 
 CSRCS += sem_destroy.c sem_wait.c sem_trywait.c sem_tickwait.c
 CSRCS += sem_timedwait.c sem_timeout.c sem_post.c sem_recover.c
-CSRCS += sem_reset.c sem_setprotocol.c sem_waitirq.c
+CSRCS += sem_reset.c sem_waitirq.c
 
 ifeq ($(CONFIG_PRIORITY_INHERITANCE),y)
-CSRCS += sem_initialize.c sem_holder.c
+CSRCS += sem_initialize.c sem_holder.c sem_setprotocol.c
 endif
 
 ifeq ($(CONFIG_SPINLOCK),y)

sched/semaphore/sem_setprotocol.c

@@ -46,6 +46,8 @@
 
 #include "semaphore/semaphore.h"
 
+#ifdef CONFIG_PRIORITY_INHERITANCE
+
 /****************************************************************************
  * Public Functions
  ****************************************************************************/
@@ -95,7 +97,6 @@ int sem_setprotocol(FAR sem_t *sem, int protocol)
   switch (protocol)
     {
       case SEM_PRIO_NONE:
-#ifdef CONFIG_PRIORITY_INHERITANCE
         /* Disable priority inheritance */
 
         sem->flags |= PRIOINHERIT_FLAGS_DISABLE;
@@ -103,16 +104,13 @@ int sem_setprotocol(FAR sem_t *sem, int protocol)
         /* Remove any current holders */
 
         sem_destroyholder(sem);
-#endif
         return OK;
 
       case SEM_PRIO_INHERIT:
-#ifdef CONFIG_PRIORITY_INHERITANCE
         /* Enable priority inheritance (dangerous) */
 
         sem->flags &= ~PRIOINHERIT_FLAGS_DISABLE;
         return OK;
-#endif
 
       case SEM_PRIO_PROTECT:
         /* Not yet supported */
@@ -128,3 +126,5 @@ int sem_setprotocol(FAR sem_t *sem, int protocol)
   set_errno(errcode);
   return ERROR;
 }
+
+endif /* CONFIG_PRIORITY_INHERITANCE */

syscall/syscall.csv

@@ -118,7 +118,7 @@
 "sem_destroy","semaphore.h","","int","FAR sem_t*"
 "sem_open","semaphore.h","defined(CONFIG_FS_NAMED_SEMAPHORES)","FAR sem_t*","FAR const char*","int","..."
 "sem_post","semaphore.h","","int","FAR sem_t*"
-"sem_setprotocol","nuttx/semaphore.h","","int","FAR sem_t*","int"
+"sem_setprotocol","nuttx/semaphore.h","defined(CONFIG_PRIORITY_INHERITANCE)","int","FAR sem_t*","int"
 "sem_timedwait","semaphore.h","","int","FAR sem_t*","FAR const struct timespec *"
 "sem_trywait","semaphore.h","","int","FAR sem_t*"
 "sem_unlink","semaphore.h","defined(CONFIG_FS_NAMED_SEMAPHORES)","int","FAR const char*"