nuttx/fs/mmap/fs_munmap.c

/****************************************************************************
 * fs/mmap/fs_munmap.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 <sys/types.h>
#include <sys/mman.h>

#include <stdint.h>
#include <errno.h>
#include <assert.h>
#include <debug.h>

#include <nuttx/kmalloc.h>

#include "inode/inode.h"
#include "fs_rammap.h"

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

/****************************************************************************
 * Name: munmap
 *
 * Description:
 *
 *   munmap() system call deletes mappings for the specified address range.
 *   All memory starting with 'start' and continuing for a length of 'length'
 *   bytes are removed.
 *
 *   NuttX operates in a flat open address space.  Therefore, it generally
 *   does not require mmap() and, hence, munmap functionality.  There are
 *   two exceptions where mmap() is available:
 *
 *   1. mmap() is the API that is used to support direct access to random
 *     access media under the following very restrictive conditions:
 *
 *     a. The filesystem supports the FIOC_MMAP ioctl command.  Any file
 *        system that maps files contiguously on the media should support
 *        this ioctl. (vs. file system that scatter files over the media
 *        in non-contiguous sectors).  As of this writing, ROMFS is the
 *        only file system that meets this requirement.
 *     b. The underlying block driver supports the BIOC_XIPBASE ioctl
 *        command that maps the underlying media to a randomly accessible
 *        address. At  present, only the RAM/ROM disk driver does this.
 *
 *     munmap() is still not required in this first case.  In this first
 *     The mapped address is a static address in the MCUs address space
 *     does not need to be munmapped.  Support for munmap() in this case
 *     provided by the simple definition in sys/mman.h:
 *
 *        #define munmap(start, length)
 *
 *   2. If CONFIG_FS_RAMMAP is defined in the configuration, then mmap() will
 *      support simulation of memory mapped files by copying files whole
 *      into RAM.  munmap() is required in this case to free the allocated
 *      memory holding the shared copy of the file.
 *
 * Input Parameters:
 *   start   The start address of the mapping to delete.  For this
 *           simplified munmap() implementation, the *must* be the start
 *           address of the memory region (the same address returned by
 *           mmap()).
 *   length  The length region to be umapped.
 *
 * Returned Value:
 *   On success, munmap() returns 0, on failure -1, and errno is set
 *   (probably to EINVAL).
 *
 ****************************************************************************/

int munmap(FAR void *start, size_t length)
{
#ifdef CONFIG_FS_RAMMAP
  FAR struct fs_rammap_s *prev;
  FAR struct fs_rammap_s *curr;
  FAR void *newaddr;
  unsigned int offset;
  int ret;
  int errcode;

  /* Find a region containing this start and length in the list of regions */

  rammap_initialize();
  ret = nxsem_wait(&g_rammaps.exclsem);
  if (ret < 0)
    {
      errcode = ret;
      goto errout;
    }

  /* Search the list of regions */

  for (prev = NULL, curr = g_rammaps.head; curr;
       prev = curr, curr = curr->flink)
    {
      /* Does this region include any part of the specified range? */

      if ((uintptr_t)start < (uintptr_t)curr->addr + curr->length &&
          (uintptr_t)start + length >= (uintptr_t)curr->addr)
        {
          break;
        }
    }

  /* Did we find the region */

  if (!curr)
    {
      ferr("ERROR: Region not found\n");
      errcode = EINVAL;
      goto errout_with_semaphore;
    }

  /* Get the offset from the beginning of the region and the actual number
   * of bytes to "unmap".  All mappings must extend to the end of the region.
   * There is no support for free a block of memory but leaving a block of
   * memory at the end.  This is a consequence of using kumm_realloc() to
   * simulate the unmapping.
   */

  offset = start - curr->addr;
  if (offset + length < curr->length)
    {
      ferr("ERROR: Cannot umap without unmapping to the end\n");
      errcode = ENOSYS;
      goto errout_with_semaphore;
    }

  /* Okay.. the region is beging umapped to the end.  Make sure the length
   * indicates that.
   */

  length = curr->length - offset;

  /* Are we unmapping the entire region (offset == 0)? */

  if (length >= curr->length)
    {
      /* Yes.. remove the mapping from the list */

      if (prev)
        {
          prev->flink = curr->flink;
        }
      else
        {
          g_rammaps.head = curr->flink;
        }

      /* Then free the region */

      kumm_free(curr);
    }

  /* No.. We have been asked to "unmap' only a portion of the memory
   * (offset > 0).
   */

  else
    {
      newaddr = kumm_realloc(curr->addr,
                             sizeof(struct fs_rammap_s) + length);
      DEBUGASSERT(newaddr == (FAR void *)(curr->addr));
      UNUSED(newaddr); /* May not be used */
      curr->length = length;
    }

  nxsem_post(&g_rammaps.exclsem);
  return OK;

errout_with_semaphore:
  nxsem_post(&g_rammaps.exclsem);

errout:
  set_errno(errcode);
  return ERROR;
#else
  return OK;
#endif /* CONFIG_FS_RAMMAP */
}