c-user: rtems_scheduler_map_priority_from_posix()

Close #3881.

c-user/scheduling_concepts.rst

@@ -40,6 +40,9 @@ The directives provided by the scheduler manager are:
 - rtems_scheduler_map_priority_to_posix_ - Map task priority to POSIX thread
   prority
 
+- rtems_scheduler_map_priority_from_posix_ - Map POSIX thread priority to task
+  prority
+
 - rtems_scheduler_get_processor_ - Get current processor index
 
 - rtems_scheduler_get_processor_maximum_ - Get processor maximum
@@ -741,6 +744,43 @@ NOTES:
 
    \clearpage
 
+.. _rtems_scheduler_map_priority_from_posix:
+
+SCHEDULER_MAP_PRIORITY_FROM_POSIX - Map POSIX thread prority to task priority
+-----------------------------------------------------------------------------
+
+CALLING SEQUENCE:
+    .. code-block:: c
+
+        rtems_status_code rtems_scheduler_map_priority_from_posix(
+            rtems_id             scheduler_id,
+            int                  posix_priority,
+            rtems_task_priority *priority
+        );
+
+DIRECTIVE STATUS CODES:
+    .. list-table::
+     :class: rtems-table
+
+     * - ``RTEMS_SUCCESSFUL``
+       - Successful operation.
+     * - ``RTEMS_INVALID_ADDRESS``
+       - The ``priority`` parameter is ``NULL``.
+     * - ``RTEMS_INVALID_ID``
+       - Invalid scheduler instance identifier.
+     * - ``RTEMS_INVALID_PRIORITY``
+       - Invalid POSIX thread priority.
+
+DESCRIPTION:
+    Maps a POSIX thread priority to the corresponding task priority.
+
+NOTES:
+    None.
+
+.. raw:: latex
+
+   \clearpage
+
 .. _rtems_scheduler_get_processor:
 
 SCHEDULER_GET_PROCESSOR - Get current processor index