nuttx/mm/mm_extend.c

/****************************************************************************
 * mm/mm_extend.c
 *
 *   Copyright (C) 2014 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 <nuttx/mm.h>

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

#define MIN_EXTEND (2 * SIZEOF_MM_ALLOCNODE)

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

/****************************************************************************
 * Name: mm_extend
 *
 * Description:
 *   Extend a heap region by add a block of (virtually) contiguous memory
 *   to the end of the heap.
 *
 ****************************************************************************/

void mm_extend(FAR struct mm_heap_s *heap, FAR void *mem, size_t size,
               int region)
{
  struct mm_allocnode_s *oldnode;
  struct mm_allocnode_s *newnode;
  uintptr_t blockstart;
  uintptr_t blockend;

  /* Make sure that we were passed valid parameters */

  DEBUGASSERT(heap && mem);
  DEBUGASSERT(size >= MIN_EXTEND && (unsigned)region < heap->mm_nregions);

  /* Make sure that the memory region are properly aligned */

  blockstart = (uintptr_t)mem;
  blockend   = blockstart + size;

  DEBUGASSERT(MM_ALIGN_UP(blockstart) == blockstart);
  DEBUGASSERT(MM_ALIGN_DOWN(blockend) == blockend);

  /* Take the memory manager semaphore */

  mm_takesemaphore(heap);

  /* Get the terminal node in the old heap.  The block to extend must
   * immediately follow this node.
   */

  oldnode = heap->mm_heapend[region];
  DEBUGASSERT((uintptr_t)oldnode + SIZEOF_MM_ALLOCNODE == (uintptr_t)mem);

  /* The size of the old node now extends to the new terminal node.
   * This is the old size (SIZEOF_MM_ALLOCNODE) plus the size of
   * the block (size) minus the size of the new terminal node
   * (SIZEOF_MM_ALLOCNODE) or simply:
   */

  oldnode->size = size;

  /* The old node should already be marked as allocated */

  DEBUGASSERT((oldnode->preceding & MM_ALLOC_BIT) != 0);

  /* Get and initialize the new terminal node in the heap */

  newnode            = (FAR struct mm_allocnode_s *)(blockend - SIZEOF_MM_ALLOCNODE);
  newnode->size      = SIZEOF_MM_ALLOCNODE;
  newnode->preceding = oldnode->size | MM_ALLOC_BIT;

  heap->mm_heapend[region] = newnode;
  mm_givesemaphore(heap);

  /* Finally "free" the new block of memory where the old terminal node was
   * located.
   */

  mm_free(heap, (FAR void *)mem);
}