nuttx/mm/mm_heap/mm_malloc_usable_size.c

/****************************************************************************
 * mm/mm_heap/mm_malloc_usable_size.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <assert.h>
#include <debug.h>
#include <malloc.h>

#include <nuttx/mm/mm.h>

#include "mm_heap/mm.h"

/****************************************************************************
 * Public Functions
 ****************************************************************************/

size_t malloc_usable_size(FAR void *mem)
{
  FAR struct mm_freenode_s *node;

  /* Protect against attempts to query a NULL reference */

  if (!mem)
    {
      return 0;
    }

  /* Map the memory chunk into a free node */

  node = (FAR struct mm_freenode_s *)((FAR char *)mem - SIZEOF_MM_ALLOCNODE);

  /* Sanity check against double-frees */

  DEBUGASSERT(node->preceding & MM_ALLOC_BIT);

  return node->size - SIZEOF_MM_ALLOCNODE;
}