fs_configfat.c

這是一個實時嵌入式作業系統 實作了MCS51 ARM等MCU

    {
      denom = fmt->ff_nfats + (var->fv_sectorsize << (fmt->ff_clustshift - 2));
      numer = navailsects + (1 << (fmt->ff_clustshift + 1)) + (1 << fmt->ff_clustshift);
    }
   return (uint32)((numer + denom - 1) / denom);
}

/****************************************************************************
 * Name:  mkfatfs_clustersearchlimits
 *
 * Description:
 *   Pick the starting and ending cluster size to use in the search for the
 *   the optimal cluster size.
 *
 * Input:
 *   fmt - Caller specified format parameters
 *   var - Other format parameters that are not caller specifiable. (Most
 *     set by mkfatfs_configfatfs()).
 *
 * Return:
 *   Starting cluster size is set in fmt->ff_clustshift; Final cluster
 *   size is the returned value.
 *
 ****************************************************************************/
static inline ubyte
mkfatfs_clustersearchlimits(FAR struct fat_format_s *fmt, FAR struct fat_var_s *var)
{
  ubyte mxclustshift;
  
  /* Did the caller already pick the cluster size?  If not, the clustshift value
   * will be 0xff
   */

  if (fmt->ff_clustshift == 0xff)
    {
      /* Pick a starting size based on the number of sectors on the device */

      if (fmt->ff_nsectors < 2048)
        {
          /* 2k sectors, start wit 1 sector/cluster. */
          fmt->ff_clustshift = 0;
        }
      else if (fmt->ff_nsectors  < 4096)
        {
          /* 4k sectors, start with 2 sector/cluster. */
          fmt->ff_clustshift = 1;
        }
      else if (fmt->ff_nsectors  < 8192)
        {
          /* 8k sectors, start with 4 sector/cluster. */
          fmt->ff_clustshift = 2;
        }
      else if (fmt->ff_nsectors  < 16384)
        {
          /* 16k sectors, start with 8 sector/cluster. */
          fmt->ff_clustshift = 3;
        }
      else if (fmt->ff_nsectors  < 32768)
        {
          /* 32k sectors, start with 16 sector/cluster. */
          fmt->ff_clustshift = 4;
        }   
      else
        {
          /* Otherwise, 32 sector/cluster. */
          fmt->ff_clustshift = 5;
        }

      /* Wherever the search starts, it will end with the maximum of
       * 128 sectors per cluster
       */

      mxclustshift = 7;
    }
  else
    {
      /* The caller has selected a cluster size.  There will be no search!
       * Just set the maximum to the caller specificed value.
       */
 
      mxclustshift = fmt->ff_clustshift;
    }
  return mxclustshift;
}

/****************************************************************************
 * Name:  mkfatfs_try12
 *
 * Description:
 *   Try to define a FAT12 filesystem on the device using the candidate
 *   sectors per cluster
 *
 * Input:
 *   fmt - Caller specified format parameters
 *   var - Other format parameters that are not caller specifiable. (Most
 *     set by mkfatfs_configfatfs()).
 *   fatconfig - FAT12-specific configuration
 *
 * Return:
 *    Zero on success configuration of a FAT12 file system; negated errno
 *    on failure
 *
 ****************************************************************************/
static inline int
mkfatfs_tryfat12(FAR struct fat_format_s *fmt, FAR struct fat_var_s *var,
                 FAR struct fat_config_s *config)
{
  uint32 maxnclusters;

  /* Calculate the number sectors in one FAT required to access all of the
   * available sectors.
   */

  config->fc_nfatsects = mkfatfs_nfatsect12(fmt, var, config->fc_navailsects);
  if (config->fc_nfatsects > 0)
    {
      /* Calculate the number of clusters available given the number of available
       * sectors and the number of those that will be used for FAT:
       */

      config->fc_nclusters =
        (config->fc_navailsects -
          fmt->ff_nfats * config->fc_nfatsects) >> fmt->ff_clustshift;

      /* Calculate the maximum number of clusters that could be supported by a
       * FAT of this size.
       *
       *   maxnclusters = nfatsects * sectorsize / 1.5 - 2
       */

      maxnclusters = (config->fc_nfatsects >> (var->fv_sectshift + 1)) / 3;
      if (maxnclusters > FAT_MAXCLUST12)
        {
          maxnclusters = FAT_MAXCLUST12;
        }
      fvdbg("nfatsects=%u nclusters=%u (max=%u)\n",
            config->fc_nfatsects, config->fc_nclusters, maxnclusters);

      /* Check if this number of clusters would overflow the maximum for
       * FAT12 (remembering that two FAT cluster slots are reserved).
       */

      if (config->fc_nclusters > maxnclusters - 2)
        {
          fvdbg("Too many clusters for FAT12\n");
          return -ENFILE;
        }
    }
  return 0;
}
 
/****************************************************************************
 * Name:  mkfatfs_try16
 *
 * Description:
 *   Try to define a FAT16 filesystem on the device using the candidate
 *   sectors per cluster
 *
 * Input:
 *   fmt - Caller specified format parameters
 *   var - Other format parameters that are not caller specifiable. (Most
 *     set by mkfatfs_configfatfs()).
 *   fatconfig - FAT16-specific configuration
 *
 * Return:
 *    Zero on success configuration of a FAT16 file system; negated errno
 *    on failure
 *
 ****************************************************************************/
static inline int
mkfatfs_tryfat16(FAR struct fat_format_s *fmt, FAR struct fat_var_s *var,
                 FAR struct fat_config_s *config)
{
  uint32 maxnclusters;

  /* Calculate the number sectors in one FAT required to access all of the
   * available sectors.
   */

  config->fc_nfatsects = mkfatfs_nfatsect16(fmt, var, config->fc_navailsects);
  if (config->fc_nfatsects > 0)
    {
      /* Calculate the number of clusters available given the number of available
       * sectors and the number of those that will be used for FAT:
       */

      config->fc_nclusters =
        (config->fc_navailsects -
          fmt->ff_nfats * config->fc_nfatsects) >> fmt->ff_clustshift;

      /* Calculate the maximum number of clusters that could be supported by a
       * FAT of this size.
       *
       *   maxnclusters = nfatsects * sectorsize / 2 - 2
       */

      maxnclusters = config->fc_nfatsects << (var->fv_sectorsize - 1);
      if (maxnclusters > FAT_MAXCLUST16)
        {
          maxnclusters = FAT_MAXCLUST16;
        }
      fvdbg("nfatsects=%u nclusters=%u (min=%u max=%u)\n",
            config->fc_nfatsects, config->fc_nclusters, FAT_MINCLUST16, maxnclusters);

      /* Check if this number of clusters would overflow the maximum for
       * FAT16 (remembering that two FAT cluster slots are reserved).
       * Check the lower limit as well.  The FAT12 is distinguished from FAT16
       * by comparing the number of clusters on the device agains a known
       * threshold.  If a small FAT16 file system were created, then it would
       * be confused as a FAT12 at mount time.
       */

      if ((config->fc_nclusters > maxnclusters - 2) ||
          (config->fc_nclusters < FAT_MINCLUST16))
        {
          fvdbg("Too few or too many clusters for FAT16\n");
          return -ENFILE;
        }
    }
  return 0;
}

/****************************************************************************
 * Name:  mkfatfs_try32
 *
 * Description:
 *   Try to define a FAT32 filesystem on the device using the candidate
 *   sectors per cluster
 *
 * Input:
 *   fmt - Caller specified format parameters
 *   var - Other format parameters that are not caller specifiable. (Most
 *     set by mkfatfs_configfatfs()).
 *   fatconfig - FAT32-specific configuration
 *
 * Return:
 *    Zero on success configuration of a FAT32 file system; negated errno
 *    on failure
 *
 ****************************************************************************/
static inline int
mkfatfs_tryfat32(FAR struct fat_format_s *fmt, FAR struct fat_var_s *var,
                 FAR struct fat_config_s *config)
{
  uint32 maxnclusters;

  /* Calculate the number sectors in one FAT required to access all of the
   * available sectors.
   */

  config->fc_nfatsects = mkfatfs_nfatsect32(fmt, var, config->fc_navailsects);
  if (config->fc_nfatsects > 0)
    {
      /* Calculate the number of clusters available given the number of available
       * sectors and the number of those that will be used for FAT:
       */

      config->fc_nclusters =
        (config->fc_navailsects -
          fmt->ff_nfats * config->fc_nfatsects) >> fmt->ff_clustshift;

      /* Calculate the maximum number of clusters that could be supported by a
       * FAT of this size.
       *
       *   maxnclusters = nfatsects * sectorsize / 4 - 2
       */

      maxnclusters = (config->fc_nfatsects >> (var->fv_sectshift - 2));
      if (maxnclusters > FAT_MAXCLUST32)
        {
          maxnclusters = FAT_MAXCLUST32;
        }
      fvdbg("nfatsects=%u nclusters=%u (max=%u)\n",
            config->fc_nfatsects, config->fc_nclusters, maxnclusters);

      /* Check if this number of clusters would overflow the maximum for
       * FAT32 (remembering that two FAT cluster slots are reserved).
       */

      if ((config->fc_nclusters > maxnclusters - 3) ||
          (config->fc_nclusters < FAT_MINCLUST32 && fmt->ff_fattype != 32))
        {
          fvdbg("Too few or too many clusters for FAT32\n");
          return -ENFILE;
        }
    }
  return 0;
}

/****************************************************************************
 * Name:  mkfatfs_selectfat
 *
 * Description:
 *   The cluster search has succeeded, select the specified FAT FS
 *
 * Input:
 *   fattype - The FAT size selected
 *   fmt     - Caller specified format parameters
 *   var     - Format parameters that are not caller specifiable.
 *
 * Return:
 *    None
 *
 ****************************************************************************/

static inline void
mkfatfs_selectfat(int fattype, FAR struct fat_format_s *fmt,
                  FAR struct fat_var_s *var, FAR struct fat_config_s *config)
{
  /* Return the appropriate information about the selected file system. */

  fdbg("Selected FAT%d\n", fattype);
  var->fv_fattype      = fattype;
  var->fv_nclusters    = config->fc_nclusters;
  var->fv_nfatsects    = config->fc_nfatsects;
  fmt->ff_rsvdseccount = config->fc_rsvdseccount;
}

/****************************************************************************
 * Name:  mkfatfs_clustersearch
 *
 * Description: