fs_configfat.c

這是一個實時嵌入式作業系統 實作了MCS51 ARM等MCU

 *   Search to find the smallest (reasonable) cluster size for the FAT file
 *   system.
 *
 * Input:
 *   fmt - Caller specified format parameters
 *   var - Other format parameters that are not caller specifiable. (Most
 *     set by mkfatfs_configfatfs()).
 *
 * Return:
 *    Zero on success; negated errno on failure
 *
 ****************************************************************************/

static inline int
mkfatfs_clustersearch(FAR struct fat_format_s *fmt, FAR struct fat_var_s *var)
{
  struct fat_config_s fatconfig[3];
  ubyte  mxclustshift;

  memset(fatconfig, 0, 3*sizeof(struct fat_config_s));

  /* Select the reserved sector count for each FAT size */

  if (fmt->ff_rsvdseccount)
    {
      fatconfig12.fc_rsvdseccount = fmt->ff_rsvdseccount;
      fatconfig16.fc_rsvdseccount = fmt->ff_rsvdseccount;

      if (fmt->ff_rsvdseccount < 2)
        {
          fvdbg("At least 2 reserved sectors needed by FAT32\n");
          fatconfig32.fc_rsvdseccount = 2;
        }
      else
        {
          fatconfig32.fc_rsvdseccount = fmt->ff_rsvdseccount;
        }
    }
  else
    {
      fatconfig12.fc_rsvdseccount = 1;
      fatconfig16.fc_rsvdseccount = 1;
      fatconfig32.fc_rsvdseccount = 32;
    }

  /* Determine the number of sectors needed by the root directory.
   * This is a constant value, independent of cluster size for FAT12/16
   */

  if (var->fv_fattype != 32)
    {
      /* Calculate the number of sectors reqired to contain the selected
       * number of root directory entries.  This value is save in the var
       * structure but will be overwritten if FAT32 is selected.  FAT32 uses
       * a cluster chain for the root directory, so the concept of the number
       * of root directory entries does not apply to FAT32
       */

      var->fv_nrootdirsects =
        ((fmt->ff_rootdirentries << DIR_SHIFT) + var->fv_sectorsize - 1) >> var->fv_sectshift;
 
      /* The number of data sectors available (includes the fat itself)
       * This value is a constant for FAT12/16, but not FAT32 because the
       * size of the root directory cluster changes
       */

      fatconfig12.fc_navailsects =
        fatconfig16.fc_navailsects =
          fmt->ff_nsectors - var->fv_nrootdirsects - fatconfig12.fc_rsvdseccount;
   }

  /* Select an initial and terminal clustersize to use in the search (if these
   * values were not provided by the caller)
   */

  mxclustshift = mkfatfs_clustersearchlimits(fmt, var);

  do
    {
      fvdbg("Configuring with %d sectors/cluster...\n", 1 << fmt->ff_clustshift);
 
      /* Check if FAT12 has not been excluded */

      if (var->fv_fattype == 0 || var->fv_fattype == 12)
        {
          /* Try to configure a FAT12 filesystem with this cluster size */

          if (mkfatfs_tryfat12(fmt, var, &fatconfig12) != 0)
            {
                {
                  fvdbg("Cannot format FAT12 at %u sectors/cluster\n", 1 << fmt->ff_clustshift);
                  fatconfig12.fc_nfatsects = 0;
                  fatconfig12.fc_nclusters = 0;
                }
            }
        }

      /* Check if FAT16 has not been excluded */

      if (var->fv_fattype == 0 || var->fv_fattype == 16)
        {
          /* Try to configure a FAT16 filesystem with this cluster size */

          if (mkfatfs_tryfat16(fmt, var, &fatconfig16) != 0)
            {
                {
                  fvdbg("Cannot format FAT16 at %u sectors/cluster\n", 1 << fmt->ff_clustshift);
                  fatconfig16.fc_nfatsects = 0;
                  fatconfig16.fc_nclusters = 0;
                }
            }
        }

      /* If either FAT12 or 16 was configured at this sector/cluster setting,
       * then finish the configuration and break out now
       */

      if (fatconfig12.fc_nclusters || fatconfig16.fc_nclusters)
        {
          if ((!var->fv_fattype && fatconfig16.fc_nclusters > fatconfig12.fc_nclusters) ||
              (var ->fv_fattype == 16))
            {
              /* The caller has selected FAT16 -OR- no FAT type has been selected, but
               * the FAT16 selection has more clusters. Select FAT16.
               */

              mkfatfs_selectfat(16, fmt, var, &fatconfig16);
            }
          else
            {
              /* The caller has selected FAT12 -OR- no FAT type has been selected, but
               * the FAT12 selected has more clusters.  Selected FAT12
               */

              mkfatfs_selectfat(12, fmt, var, &fatconfig12);
            }
         return OK;
        }

      /* Check if FAT32 has not been excluded */

      if (var->fv_fattype == 0 || var->fv_fattype == 32)
        {
          /* The number of data sectors available (includes the fat itself)
           * This value is a constant with respect to cluster sizefor FAT12/16, but not FAT32
           * because the size of the root directory cluster changes with cluster size.
           */

          fatconfig32.fc_navailsects = fmt->ff_nsectors - (1 << fmt->ff_clustshift) - fatconfig32.fc_rsvdseccount;

          /* Try to configure a FAT32 filesystem with this cluster size */

          if (mkfatfs_tryfat32(fmt, var, &fatconfig32) != 0)
            {
                {
                  fvdbg("Cannot format FAT32 at %u sectors/cluster\n", 1 << fmt->ff_clustshift);
                  fatconfig32.fc_nfatsects = 0;
                  fatconfig32.fc_nclusters = 0;
                }
            }
          else
            {
              /* Select FAT32 if we have not already done so */

              mkfatfs_selectfat(32, fmt, var, &fatconfig32);
              return OK;
            }
        }

      /* Otherwise, bump up the sectors/cluster for the next time around the loop. */

      fmt->ff_clustshift++;
    }
  while (fmt->ff_clustshift <= mxclustshift);
  return -ENFILE;
}

/****************************************************************************
 * Global Functions
 ****************************************************************************/

/****************************************************************************
 * Name: mkfatfs_configfatfs
 *
 * Description:
 *   Based on the geometry of the block device and upon the caller-selected
 *   values, configure the FAT filesystem for the device.
 *
 * Input:
 *    fmt  - Caller specified format parameters
 *    var  - Holds disk geomtry data.  Also, the location to return FAT
 *           configuration data
 *
 * Return:
 *    Zero on success; negated errno on failure
 *
 ****************************************************************************/
int mkfatfs_configfatfs(FAR struct fat_format_s *fmt,
                        FAR struct fat_var_s *var)
{
  int ret;

  /* Select the number of root directory entries (FAT12/16 only).  If FAT32 is selected,
   * this value will be cleared later
   */

  if (!fmt->ff_rootdirentries)
    {
      /* The caller did not specify the number of root directory entries; use a default of 512. */

      fmt->ff_rootdirentries = 512;
    }

  /* Search to determine the smallest (reasonable) cluster size.  A by-product
   * of this search will be the selection of the FAT size (12/16/32) if the
   * caller has not specified the FAT size
   */

  ret = mkfatfs_clustersearch(fmt, var);
  if (ret < 0)
    {
       fdbg("Failed to set cluster size\n");
       return ret;
    }

  /* Perform FAT specific initialization */

  /* Set up boot jump assuming FAT 12/16 offset to bootcode */

  var->fv_jump[0]      = OPCODE_JMP_REL8;
  var->fv_jump[2]      = OPCODE_NOP;
  var->fv_bootcode     = g_bootcodeblob;
  var->fv_bootcodesize = sizeof(g_bootcodeblob);

  if (var->fv_fattype != 32)
    {
      /* Set up additional, non-zero FAT12/16 fields */

      /* Patch in the correct offset to the boot code */
 
      var->fv_jump[1]   = BS16_BOOTCODE - 2;
      g_bootcodeblob[3] = BS16_BOOTCODE + BOOTCODE_MSGOFFSET;
    }
  else
    {
      /* Patch in the correct offset to the boot code */

      var->fv_jump[1]   = BS32_BOOTCODE - 2;
      g_bootcodeblob[3] = BS32_BOOTCODE + BOOTCODE_MSGOFFSET;

      /* The root directory is a cluster chain... its is initialize size is one cluster */
  
      var->fv_nrootdirsects = 1 << fmt->ff_clustshift;

      /* The number of reported root directory entries should should be zero for
       * FAT32 because the root directory is a cluster chain.
       */

      fmt->ff_rootdirentries = 0;

      /* Verify the caller's backupboot selection */

      if (fmt->ff_backupboot <= 1 || fmt->ff_backupboot >= fmt->ff_rsvdseccount)
        {
          fdbg("Invalid backup boot sector: %d\n", fmt->ff_backupboot);
          fmt->ff_backupboot = 0;
        }

     /* Check if the caller has selected a location for the backup boot record */

      if (!fmt->ff_backupboot)
        {
          /* There must be reserved sectors in order to have a backup boot sector */

          if (fmt->ff_rsvdseccount > 0 && fmt->ff_rsvdseccount >= 2)
            {
              /* Sector 0 is the MBR; 1... ff_rsvdseccount are reserved.  Try the next
               * the last reserved sector.
               */

              fmt->ff_backupboot = fmt->ff_rsvdseccount - 1;
              if (fmt->ff_backupboot > 6)
                {
                  /* Limit the location to within the first 7 */

                  fmt->ff_backupboot = 6;
                }
            }
        }
    }

  /* Report the selected fat type */

  fmt->ff_fattype = var->fv_fattype;

  /* Describe the configured filesystem */

#ifdef CONFIG_DEBUG
  fdbg("Sector size:          %d bytes\n", var->fv_sectorsize);
  fdbg("Number of sectors:    %d sectors\n", fmt->ff_nsectors);
  fdbg("FAT size:             %d bits\n", var->fv_fattype);
  fdbg("Number FATs:          %d\n", fmt->ff_nfats);
  fdbg("Sectors per cluster:  %d sectors\n", 1 << fmt->ff_clustshift);
  fdbg("FS size:              %d sectors\n", var->fv_nfatsects);
  fdbg("                      %d clusters\n", var->fv_nclusters);
  if (var->fv_fattype != 32)
    {
       fdbg("Root directory slots: %d\n", fmt->ff_rootdirentries);
    }
  fdbg("Volume ID:            %08x\n", fmt->ff_volumeid);
  fdbg("Volume Label:         \"%c%c%c%c%c%c%c%c%c%c%c\"\n",
    fmt->ff_volumelabel[0], fmt->ff_volumelabel[1], fmt->ff_volumelabel[2], 
    fmt->ff_volumelabel[3], fmt->ff_volumelabel[4], fmt->ff_volumelabel[5], 
    fmt->ff_volumelabel[6], fmt->ff_volumelabel[7], fmt->ff_volumelabel[8], 
    fmt->ff_volumelabel[9], fmt->ff_volumelabel[10]);
#endif
  return OK;
}