Erreur grub filesystem FAT

static struct grub_fat_data *
grub_fat_mount (grub_disk_t disk)
{
  struct grub_fat_bpb bpb;
  struct grub_fat_data *data = 0;
  grub_uint32_t first_fat, magic;

  if (! disk)
    goto fail;

  data = (struct grub_fat_data *) grub_malloc (sizeof (*data));
  if (! data)
    goto fail;

  /* Read the BPB.  */
  if (grub_disk_read (disk, 0, 0, sizeof (bpb), &bpb))
    goto fail;

  if (grub_strncmp((const char *) bpb.version_specific.fat12_or_fat16.fstype, "FAT12", 5)
      && grub_strncmp((const char *) bpb.version_specific.fat12_or_fat16.fstype, "FAT16", 5)
      && grub_strncmp((const char *) bpb.version_specific.fat32.fstype, "FAT32", 5))
    goto fail;

  /* Get the sizes of logical sectors and clusters.  */
  data->logical_sector_bits =
    fat_log2 (grub_le_to_cpu16 (bpb.bytes_per_sector));
  if (data->logical_sector_bits < GRUB_DISK_SECTOR_BITS)
    goto fail;
  data->logical_sector_bits -= GRUB_DISK_SECTOR_BITS;

  data->cluster_bits = fat_log2 (bpb.sectors_per_cluster);
  if (data->cluster_bits < 0)
    goto fail;
  data->cluster_bits += data->logical_sector_bits;

  /* Get information about FATs.  */
  data->fat_sector = (grub_le_to_cpu16 (bpb.num_reserved_sectors)
              << data->logical_sector_bits);
  if (data->fat_sector == 0)
    goto fail;

  data->sectors_per_fat = ((bpb.sectors_per_fat_16
                ? grub_le_to_cpu16 (bpb.sectors_per_fat_16)
                : grub_le_to_cpu32 (bpb.version_specific.fat32.sectors_per_fat_32))
               << data->logical_sector_bits);
  if (data->sectors_per_fat == 0)
    goto fail;

  /* Get the number of sectors in this volume.  */
  data->num_sectors = ((bpb.num_total_sectors_16
            ? grub_le_to_cpu16 (bpb.num_total_sectors_16)
            : grub_le_to_cpu32 (bpb.num_total_sectors_32))
               << data->logical_sector_bits);
  if (data->num_sectors == 0)
    goto fail;

  /* Get information about the root directory.  */
  if (bpb.num_fats == 0)
    goto fail;

  data->root_sector = data->fat_sector + bpb.num_fats * data->sectors_per_fat;
  data->num_root_sectors
    = ((((grub_uint32_t) grub_le_to_cpu16 (bpb.num_root_entries)
     * GRUB_FAT_DIR_ENTRY_SIZE
     + grub_le_to_cpu16 (bpb.bytes_per_sector) - 1)
    >> (data->logical_sector_bits + GRUB_DISK_SECTOR_BITS))
       << (data->logical_sector_bits));

  data->cluster_sector = data->root_sector + data->num_root_sectors;
  data->num_clusters = (((data->num_sectors - data->cluster_sector)
             >> (data->cluster_bits + data->logical_sector_bits))
            + 2);

  if (data->num_clusters <= 2)
    goto fail;

  if (! bpb.sectors_per_fat_16)
    {
      /* FAT32.  */
      grub_uint16_t flags = grub_le_to_cpu16 (bpb.version_specific.fat32.extended_flags);

      data->root_cluster = grub_le_to_cpu32 (bpb.version_specific.fat32.root_cluster);
      data->fat_size = 32;
      data->cluster_eof_mark = 0x0ffffff8;

      if (flags & 0x80)
    {
      /* Get an active FAT.  */
      unsigned active_fat = flags & 0xf;

      if (active_fat > bpb.num_fats)
        goto fail;

      data->fat_sector += active_fat * data->sectors_per_fat;
    }

      if (bpb.num_root_entries != 0 || bpb.version_specific.fat32.fs_version != 0)
    goto fail;
    }
  else
    {
      /* FAT12 or FAT16.  */
      data->root_cluster = ~0U;

      if (data->num_clusters <= 4085 + 2)
    {
      /* FAT12.  */
      data->fat_size = 12;
      data->cluster_eof_mark = 0x0ff8;
    }
      else
    {
      /* FAT16.  */
      data->fat_size = 16;
      data->cluster_eof_mark = 0xfff8;
    }
    }

  /* More sanity checks.  */
  if (data->num_sectors <= data->fat_sector)
    goto fail;

  if (grub_disk_read (disk,
              data->fat_sector,
              0,
              sizeof (first_fat),
              &first_fat))
    goto fail;

  first_fat = grub_le_to_cpu32 (first_fat);

  if (data->fat_size == 32)
    {
      first_fat &= 0x0fffffff;
      magic = 0x0fffff00;
    }
  else if (data->fat_size == 16)
    {
      first_fat &= 0x0000ffff;
      magic = 0xff00;
    }
  else
    {
      first_fat &= 0x00000fff;
      magic = 0x0f00;
    }

  /* Serial number.  */
  if (bpb.sectors_per_fat_16)
    data->uuid = grub_le_to_cpu32 (bpb.version_specific.fat12_or_fat16.num_serial);
  else
    data->uuid = grub_le_to_cpu32 (bpb.version_specific.fat32.num_serial);

  /* Ignore the 3rd bit, because some BIOSes assigns 0xF0 to the media
     descriptor, even if it is a so-called superfloppy (e.g. an USB key).
     The check may be too strict for this kind of stupid BIOSes, as
     they overwrite the media descriptor.  */
  if ((first_fat | 0x8) != (magic | bpb.media | 0x8))
    goto fail;

  /* Start from the root directory.  */
  data->file_cluster = data->root_cluster;
  data->cur_cluster_num = ~0U;
  data->attr = GRUB_FAT_ATTR_DIRECTORY;
  return data;

 fail:

  grub_free (data);
  grub_error (GRUB_ERR_BAD_FS, "not a FAT filesystem");
  return 0;
}