fs_fat32util.c

這是一個實時嵌入式作業系統 實作了MCS51 ARM等MCU

                  startsector >>= 4;
                }
              else
                {
                  /* Even.. take the LS 12-bits */
                  startsector &= 0x0fff;
                }
              return startsector;
            }

          case FSTYPE_FAT16 :
            {
              unsigned int fatoffset = 2 * clusterno;
              size_t       fatsector = fs->fs_fatbase + SEC_NSECTORS(fs, fatoffset);
              unsigned int fatindex  = fatoffset & SEC_NDXMASK(fs);

              if (fat_fscacheread(fs, fatsector) < 0)
                {
                  /* Read error */
                  break;
                }
              return FAT_GETFAT16(fs->fs_buffer, fatindex);
            }

          case FSTYPE_FAT32 :
            {
              unsigned int fatoffset = 4 * clusterno;
              size_t       fatsector = fs->fs_fatbase + SEC_NSECTORS(fs, fatoffset);
              unsigned int fatindex  = fatoffset & SEC_NDXMASK(fs);

              if (fat_fscacheread(fs, fatsector) < 0)
                {
                  /* Read error */
                  break;
                }
              return FAT_GETFAT16(fs->fs_buffer, fatindex) & 0x0fffffff;
            }
          default:
              break;
        }
    }

  /* There is no cluster information, or an error occured */

  return (ssize_t)-EINVAL;
}

/****************************************************************************
 * Name: fat_putcluster
 *
 * Desciption: Write a new cluster start sector into the FAT
 *
 ****************************************************************************/

int fat_putcluster(struct fat_mountpt_s *fs, uint32 clusterno, size_t startsector)
{
  /* Verify that the cluster number is within range.  Zero erases the cluster. */

  if (clusterno == 0 || (clusterno >= 2 && clusterno < fs->fs_nclusters))
    {
      /* Okay.. Write the next cluster into the FAT.  The way we will do
       * this depends on the type of FAT filesystm we are dealing with.
       */

      switch (fs->fs_type)
        {
          case FSTYPE_FAT12 :
            {
              size_t       fatsector;
              unsigned int fatoffset;
              unsigned int fatindex;
              ubyte        value;

              /* FAT12 is more complex because it has 12-bits (1.5 bytes)
               * per FAT entry. Get the offset to the first byte:
               */

              fatoffset = (clusterno * 3) / 2;
              fatsector = fs->fs_fatbase + SEC_NSECTORS(fs, fatoffset);

              /* Make sure that the sector at this offset is in the cache */

              if (fat_fscacheread(fs, fatsector)< 0)
                {
                  /* Read error */
                  break;
                }

              /* Output the LS byte first handling the 12-bit alignment within
               * the 16-bits
               */

              fatindex = fatoffset & SEC_NDXMASK(fs);
              if ((clusterno & 1) != 0)
                {
                  value = (fs->fs_buffer[fatindex] & 0x0f) | startsector << 4;
                }
              else
                {
                  value = (ubyte)startsector;
                }
              fs->fs_buffer[fatindex] = value;

              /* With FAT12, the second byte of the cluster number may lie in
               * a different sector than the first byte.
               */

              fatindex++;
              if (fatindex >= fs->fs_hwsectorsize)
                {
                  /* Read the next sector */

                  fatsector++;
                  fatindex = 0;

                  /* Set the dirty flag to make sure the sector that we
                   * just modified is written out.
                   */

                  fs->fs_dirty = TRUE;
                  if (fat_fscacheread(fs, fatsector) < 0)
                    {
                      /* Read error */
                      break;
                    }
                }

              /* Output the MS byte first handling the 12-bit alignment within
               * the 16-bits
               */

              if ((clusterno & 1) != 0)
                {
                  value = (ubyte)(startsector >> 4);
                }
              else
                {
                  value = (fs->fs_buffer[fatindex] & 0xf0) | (startsector & 0x0f);
                }
              fs->fs_buffer[fatindex] = value;
            }
          break;

          case FSTYPE_FAT16 :
            {
              unsigned int fatoffset = 2 * clusterno;
              size_t       fatsector = fs->fs_fatbase + SEC_NSECTORS(fs, fatoffset);
              unsigned int fatindex  = fatoffset & SEC_NDXMASK(fs);

              if (fat_fscacheread(fs, fatsector) < 0)
                {
                  /* Read error */
                  break;
                }
              FAT_PUTFAT16(fs->fs_buffer, fatindex, startsector & 0xffff);
            }
          break;

          case FSTYPE_FAT32 :
            {
              unsigned int fatoffset = 4 * clusterno;
              size_t       fatsector = fs->fs_fatbase + SEC_NSECTORS(fs, fatoffset);
              unsigned int fatindex  = fatoffset & SEC_NDXMASK(fs);

              if (fat_fscacheread(fs, fatsector) < 0)
                {
                  /* Read error */
                  break;
                }
              FAT_PUTFAT32(fs->fs_buffer, fatindex, startsector & 0x0fffffff);
            }
          break;

          default:
              return -EINVAL;
        }

      /* Mark the modified sector as "dirty" and return success */

      fs->fs_dirty = 1;
      return OK;
    }

  return -EINVAL;
}

/****************************************************************************
 * Name: fat_removechain
 *
 * Desciption: Remove an entire chain of clusters, starting with 'cluster'
 *
 ****************************************************************************/

int fat_removechain(struct fat_mountpt_s *fs, uint32 cluster)
{
  sint32 nextcluster;
  int    ret;

  /* Loop while there are clusters in the chain */

  while (cluster >= 2 && cluster < fs->fs_nclusters)
    {
      /* Get the next cluster after the current one */

      nextcluster = fat_getcluster(fs, cluster);
      if (nextcluster < 0)
        {
          /* Error! */
          return nextcluster;
        }

      /* Then nullify current cluster -- removing it from the chain */

      ret = fat_putcluster(fs, cluster, 0);
      if (ret < 0)
        {
          return ret;
        }

      /* Update FSINFINFO data */

      if (fs->fs_fsifreecount != 0xffffffff)
        {
          fs->fs_fsifreecount++;
          fs->fs_fsidirty = 1;
        }

      /* Then set up to remove the next cluster */

      cluster = nextcluster;
  }

  return OK;
}

/****************************************************************************
 * Name: fat_extendchain
 *
 * Desciption: Add a new cluster to the chain following cluster (if cluster
 *   is non-NULL).  if cluster is zero, then a new chain is created.
 *
 * Return: <0:error, 0: no free cluster, >=2: new cluster number
 *
 ****************************************************************************/

sint32 fat_extendchain(struct fat_mountpt_s *fs, uint32 cluster)
{
  ssize_t startsector;
  uint32  newcluster;
  uint32  startcluster;
  int     ret;

  /* The special value 0 is used when the new chain should start */

  if (cluster == 0)
    {
      /* The FSINFO NextFree entry should be a good starting point
       * in the search for a new cluster
       */

      startcluster = fs->fs_fsinextfree;
      if (startcluster == 0 || startcluster >= fs->fs_nclusters)
        {
          /* But it is bad.. we have to start at the beginning */
          startcluster = 1;
        }
    }
  else
    {
      /* We are extending an existing chain. Verify that this
       * is a valid cluster by examining its start sector.
       */

      startsector = fat_getcluster(fs, cluster);
      if (startsector < 0)
        {
          /* An error occurred, return the error value */
          return startsector;
        }
      else if (startsector < 2)
        {
          /* Oops.. this cluster does not exist. */
          return 0;
        }
      else if (startsector < fs->fs_nclusters)
        {
          /* It is already followed by next cluster */
          return startsector;
        }

      /* Okay.. it checks out */

      startcluster = cluster;
    }

  /* Loop until (1) we discover that there are not free clusters
   * (return 0), an errors occurs (return -errno), or (3) we find
   * the next cluster (return the new cluster number).
   */

  newcluster = startcluster;
  for (;;)
    {
      /* Examine the next cluster in the FAT */

      newcluster++;
      if (newcluster >= fs->fs_nclusters)
        {
          /* If we hit the end of the available clusters, then
           * wrap back to the beginning because we might have
           * started at a non-optimal place.  But don't continue
           * past the start cluster.
           */

          newcluster = 2;
          if (newcluster > startcluster)
            {
              /* We are back past the starting cluster, then there
               * is no free cluster.
               */

              return 0;
            }
        }

      /* We have a candidate cluster.  Check if the cluster number is
       * mapped to a group of sectors.
       */

      startsector = fat_getcluster(fs, newcluster);
      if (startsector == 0)
        {
          /* Found have found a free cluster break out*/
          break;
        }
      else if (startsector < 0)
        {
          /* Some error occurred, return the error number */
          return startsector;
        }

      /* We wrap all the back to the starting cluster?  If so, then
       * there are no free clusters.
       */

      if (newcluster == startcluster)
        {
          return 0;
        }
    }

  /* We get here only if we break out with an available cluster
   * number in 'newcluster'  Now mark that cluster as in-use.
   */

  ret = fat_putcluster(fs, newcluster, 0x0fffffff);
  if (ret < 0)
    {
      /* An error occurred */ 
      return ret;
    }

  /* And link if to the start cluster (if any)*/

  if (cluster)
    {
      /* There is a start cluster -- link it */

      ret = fat_putcluster(fs, cluster, newcluster);
      if (ret < 0)
        {
          return ret;
        }
    }

  /* And update the FINSINFO for the next time we have to search */

  fs->fs_fsinextfree = newcluster;
  if (fs->fs_fsifreecount != 0xffffffff)
    {
      fs->fs_fsifreecount--;
      fs->fs_fsidirty = 1;
    }

  /* Return then number of the new cluster that was added to the chain */

  return newcluster;
}

/****************************************************************************
 * Name: fat_nextdirentry
 *
 * Desciption: Read the next directory entry from the sector in cache,
 *   reading the next sector(s) in the cluster as necessary.
 *
 ****************************************************************************/

int fat_nextdirentry(struct fat_mountpt_s *fs, struct fs_fatdir_s *dir)
{
  unsigned int cluster;
  unsigned int ndx;

  /* Increment the index to the next 32-byte directory entry */

  ndx = dir->fd_index + 1;

  /* Check if all of the directory entries in this sectory have
   * been examined.
   */

  if ((ndx & (DIRSEC_NDIRS(fs)-1)) == 0)
    {
      /* Yes, then we will have to read the next sector */

      dir->fd_currsector++;

      /* For FAT12/16, the root directory is a group of sectors relative
       * to the first sector of the fat volume.
       */

      if (!dir->fd_currcluster)
        {
          /* For FAT12/16, the boot record tells us number of 32-bit directories
           * that are contained in the root directory.  This should correspond to
           * an even number of sectors.
           */

          if (ndx >= fs->fs_rootentcnt)
            {
              /* When we index past this count, we have examined all of the entries in
               * the root directory.
               */

              return ERROR;
            }
        }
      else
        {
          /* Not a FAT12/16 root directory, check if we have examined the entire
           * cluster comprising the directory.
           *
           * The current sector within the cluster is the entry number divided
           * byte the number of entries per sector
           */

          int sector = ndx / DIRSEC_NDIRS(fs);

          /* We are finished with the cluster when the last sector of the cluster
           * has been examined.
           */

          if ((sector & (fs->fs_fatsecperclus-1)) == 0)
            {
              /* Get next cluster */

              cluster = fat_getcluster(fs, dir->fd_currcluster);

              /* Check if a valid cluster was obtained. */

              if (cluster < 2 || cluster >= fs->fs_nclusters)
                {
                  /* No, we have probably reached the end of the cluster list */
                  return ERROR;
                }

              /* Initialize for new cluster */