nodemcu-firmware/app/spiffs/spiffs_nucleus.c

#include "spiffs.h"
#include "spiffs_nucleus.h"

static s32_t spiffs_page_data_check(spiffs *fs, spiffs_fd *fd, spiffs_page_ix pix, spiffs_span_ix spix) {
  s32_t res = SPIFFS_OK;
  if (pix == (spiffs_page_ix)-1) {
    // referring to page 0xffff...., bad object index
    return SPIFFS_ERR_INDEX_REF_FREE;
  }
  if (pix % SPIFFS_PAGES_PER_BLOCK(fs) < SPIFFS_OBJ_LOOKUP_PAGES(fs)) {
    // referring to an object lookup page, bad object index
    return SPIFFS_ERR_INDEX_REF_LU;
  }
  if (pix > SPIFFS_MAX_PAGES(fs)) {
    // referring to a bad page
    return SPIFFS_ERR_INDEX_REF_INVALID;
  }
#if SPIFFS_PAGE_CHECK
  spiffs_page_header ph;
  res = _spiffs_rd(
      fs, SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_READ,
      fd->file_nbr,
      SPIFFS_PAGE_TO_PADDR(fs, pix),
      sizeof(spiffs_page_header),
      (u8_t *)&ph);
  SPIFFS_CHECK_RES(res);
  SPIFFS_VALIDATE_DATA(ph, fd->obj_id & ~SPIFFS_OBJ_ID_IX_FLAG, spix);
#endif
  return res;
}

#if !SPIFFS_READ_ONLY
static s32_t spiffs_page_index_check(spiffs *fs, spiffs_fd *fd, spiffs_page_ix pix, spiffs_span_ix spix) {
  s32_t res = SPIFFS_OK;
  if (pix == (spiffs_page_ix)-1) {
    // referring to page 0xffff...., bad object index
    return SPIFFS_ERR_INDEX_FREE;
  }
  if (pix % SPIFFS_PAGES_PER_BLOCK(fs) < SPIFFS_OBJ_LOOKUP_PAGES(fs)) {
    // referring to an object lookup page, bad object index
    return SPIFFS_ERR_INDEX_LU;
  }
  if (pix > SPIFFS_MAX_PAGES(fs)) {
    // referring to a bad page
    return SPIFFS_ERR_INDEX_INVALID;
  }
#if SPIFFS_PAGE_CHECK
  spiffs_page_header ph;
  res = _spiffs_rd(
      fs, SPIFFS_OP_T_OBJ_IX | SPIFFS_OP_C_READ,
      fd->file_nbr,
      SPIFFS_PAGE_TO_PADDR(fs, pix),
      sizeof(spiffs_page_header),
      (u8_t *)&ph);
  SPIFFS_CHECK_RES(res);
  SPIFFS_VALIDATE_OBJIX(ph, fd->obj_id, spix);
#endif
  return res;
}
#endif // !SPIFFS_READ_ONLY

#if !SPIFFS_CACHE

s32_t spiffs_phys_rd(
    spiffs *fs,
    u32_t addr,
    u32_t len,
    u8_t *dst) {
  return SPIFFS_HAL_READ(fs, addr, len, dst);
}

s32_t spiffs_phys_wr(
    spiffs *fs,
    u32_t addr,
    u32_t len,
    u8_t *src) {
  return SPIFFS_HAL_WRITE(fs, addr, len, src);
}

#endif

#if !SPIFFS_READ_ONLY
s32_t spiffs_phys_cpy(
    spiffs *fs,
    spiffs_file fh,
    u32_t dst,
    u32_t src,
    u32_t len) {
  (void)fh;
  s32_t res;
  u8_t b[SPIFFS_COPY_BUFFER_STACK];
  while (len > 0) {
    u32_t chunk_size = MIN(SPIFFS_COPY_BUFFER_STACK, len);
    res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_MOVS, fh, src, chunk_size, b);
    SPIFFS_CHECK_RES(res);
    res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_MOVD,  fh, dst, chunk_size, b);
    SPIFFS_CHECK_RES(res);
    len -= chunk_size;
    src += chunk_size;
    dst += chunk_size;
  }
  return SPIFFS_OK;
}
#endif // !SPIFFS_READ_ONLY

// Find object lookup entry containing given id with visitor.
// Iterate over object lookup pages in each block until a given object id entry is found.
// When found, the visitor function is called with block index, entry index and user data.
// If visitor returns SPIFFS_VIS_CONTINUE, the search goes on. Otherwise, the search will be
// ended and visitor's return code is returned to caller.
// If no visitor is given (0) the search returns on first entry with matching object id.
// If no match is found in all look up, SPIFFS_VIS_END is returned.
// @param fs                    the file system
// @param starting_block        the starting block to start search in
// @param starting_lu_entry     the look up index entry to start search in
// @param flags                 ored combination of SPIFFS_VIS_CHECK_ID, SPIFFS_VIS_CHECK_PH,
//                              SPIFFS_VIS_NO_WRAP
// @param obj_id                argument object id
// @param v                     visitor callback function
// @param user_const_p          any const pointer, passed to the callback visitor function
// @param user_var_p            any pointer, passed to the callback visitor function
// @param block_ix              reported block index where match was found
// @param lu_entry              reported look up index where match was found
s32_t spiffs_obj_lu_find_entry_visitor(
    spiffs *fs,
    spiffs_block_ix starting_block,
    int starting_lu_entry,
    u8_t flags,
    spiffs_obj_id obj_id,
    spiffs_visitor_f v,
    const void *user_const_p,
    void *user_var_p,
    spiffs_block_ix *block_ix,
    int *lu_entry) {
  s32_t res = SPIFFS_OK;
  s32_t entry_count = fs->block_count * SPIFFS_OBJ_LOOKUP_MAX_ENTRIES(fs);
  spiffs_block_ix cur_block = starting_block;
  u32_t cur_block_addr = starting_block * SPIFFS_CFG_LOG_BLOCK_SZ(fs);

  spiffs_obj_id *obj_lu_buf = (spiffs_obj_id *)fs->lu_work;
  int cur_entry = starting_lu_entry;
  int entries_per_page = (SPIFFS_CFG_LOG_PAGE_SZ(fs) / sizeof(spiffs_obj_id));

  // wrap initial
  if (cur_entry >= (int)SPIFFS_OBJ_LOOKUP_MAX_ENTRIES(fs) - 1) {
    cur_entry = 0;
    cur_block++;
    cur_block_addr = cur_block * SPIFFS_CFG_LOG_BLOCK_SZ(fs);
    if (cur_block >= fs->block_count) {
      if (flags & SPIFFS_VIS_NO_WRAP) {
        return SPIFFS_VIS_END;
      } else {
        // block wrap
        cur_block = 0;
        cur_block_addr = 0;
      }
    }
  }

  // check each block
  while (res == SPIFFS_OK && entry_count > 0) {
    int obj_lookup_page = cur_entry / entries_per_page;
    // check each object lookup page
    while (res == SPIFFS_OK && obj_lookup_page < (int)SPIFFS_OBJ_LOOKUP_PAGES(fs)) {
      int entry_offset = obj_lookup_page * entries_per_page;
      res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_LU | SPIFFS_OP_C_READ,
          0, cur_block_addr + SPIFFS_PAGE_TO_PADDR(fs, obj_lookup_page), SPIFFS_CFG_LOG_PAGE_SZ(fs), fs->lu_work);
      // check each entry
      while (res == SPIFFS_OK &&
          cur_entry - entry_offset < entries_per_page && // for non-last obj lookup pages
          cur_entry < (int)SPIFFS_OBJ_LOOKUP_MAX_ENTRIES(fs)) // for last obj lookup page
      {
        if ((flags & SPIFFS_VIS_CHECK_ID) == 0 || obj_lu_buf[cur_entry-entry_offset] == obj_id) {
          if (block_ix) *block_ix = cur_block;
          if (lu_entry) *lu_entry = cur_entry;
          if (v) {
            res = v(
                fs,
                (flags & SPIFFS_VIS_CHECK_PH) ? obj_id : obj_lu_buf[cur_entry-entry_offset],
                cur_block,
                cur_entry,
                user_const_p,
                user_var_p);
            if (res == SPIFFS_VIS_COUNTINUE || res == SPIFFS_VIS_COUNTINUE_RELOAD) {
              if (res == SPIFFS_VIS_COUNTINUE_RELOAD) {
                res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_LU | SPIFFS_OP_C_READ,
                    0, cur_block_addr + SPIFFS_PAGE_TO_PADDR(fs, obj_lookup_page), SPIFFS_CFG_LOG_PAGE_SZ(fs), fs->lu_work);
                SPIFFS_CHECK_RES(res);
              }
              res = SPIFFS_OK;
              cur_entry++;
              entry_count--;
              continue;
            } else {
              return res;
            }
          } else {
            return SPIFFS_OK;
          }
        }
        entry_count--;
        cur_entry++;
      } // per entry
      obj_lookup_page++;
    } // per object lookup page
    cur_entry = 0;
    cur_block++;
    cur_block_addr += SPIFFS_CFG_LOG_BLOCK_SZ(fs);
    if (cur_block >= fs->block_count) {
      if (flags & SPIFFS_VIS_NO_WRAP) {
        return SPIFFS_VIS_END;
      } else {
        // block wrap
        cur_block = 0;
        cur_block_addr = 0;
      }
    }
  } // per block

  SPIFFS_CHECK_RES(res);

  return SPIFFS_VIS_END;
}

#if !SPIFFS_READ_ONLY
s32_t spiffs_erase_block(
    spiffs *fs,
    spiffs_block_ix bix) {
  s32_t res;
  u32_t addr = SPIFFS_BLOCK_TO_PADDR(fs, bix);
  s32_t size = SPIFFS_CFG_LOG_BLOCK_SZ(fs);

  // here we ignore res, just try erasing the block
  while (size > 0) {
    SPIFFS_DBG("erase %08x:%08x\n", addr,  SPIFFS_CFG_PHYS_ERASE_SZ(fs));
    SPIFFS_HAL_ERASE(fs, addr, SPIFFS_CFG_PHYS_ERASE_SZ(fs));

    addr += SPIFFS_CFG_PHYS_ERASE_SZ(fs);
    size -= SPIFFS_CFG_PHYS_ERASE_SZ(fs);
  }
  fs->free_blocks++;

  // register erase count for this block
  res = _spiffs_wr(fs, SPIFFS_OP_C_WRTHRU | SPIFFS_OP_T_OBJ_LU2, 0,
      SPIFFS_ERASE_COUNT_PADDR(fs, bix),
      sizeof(spiffs_obj_id), (u8_t *)&fs->max_erase_count);
  SPIFFS_CHECK_RES(res);

#if SPIFFS_USE_MAGIC
  // finally, write magic
  spiffs_obj_id magic = SPIFFS_MAGIC(fs, bix);
  res = _spiffs_wr(fs, SPIFFS_OP_C_WRTHRU | SPIFFS_OP_T_OBJ_LU2, 0,
      SPIFFS_MAGIC_PADDR(fs, bix),
      sizeof(spiffs_obj_id), (u8_t *)&magic);
  SPIFFS_CHECK_RES(res);
#endif

  fs->max_erase_count++;
  if (fs->max_erase_count == SPIFFS_OBJ_ID_IX_FLAG) {
    fs->max_erase_count = 0;
  }

  return res;
}
#endif // !SPIFFS_READ_ONLY

#if SPIFFS_USE_MAGIC && SPIFFS_USE_MAGIC_LENGTH && SPIFFS_SINGLETON==0
s32_t spiffs_probe(
    spiffs_config *cfg) {
  s32_t res;
  u32_t paddr;
  spiffs dummy_fs; // create a dummy fs struct just to be able to use macros
  memcpy(&dummy_fs.cfg, cfg, sizeof(spiffs_config));
  dummy_fs.block_count = 0;

  // Read three magics, as one block may be in an aborted erase state.
  // At least two of these must contain magic and be in decreasing order.
  spiffs_obj_id magic[3];
  spiffs_obj_id bix_count[3];

  spiffs_block_ix bix;
  for (bix = 0; bix < 3; bix++) {
    paddr = SPIFFS_MAGIC_PADDR(&dummy_fs, bix);
#if SPIFFS_HAL_CALLBACK_EXTRA
    // not any proper fs to report here, so callback with null
    // (cross fingers that no-one gets angry)
    res = cfg->hal_read_f((void *)0, paddr, sizeof(spiffs_obj_id), (u8_t *)&magic[bix]);
#else
    res = cfg->hal_read_f(paddr, sizeof(spiffs_obj_id), (u8_t *)&magic[bix]);
#endif
    bix_count[bix] = magic[bix] ^ SPIFFS_MAGIC(&dummy_fs, 0);
    SPIFFS_CHECK_RES(res);
  }

  // check that the order is correct, take aborted erases in calculation
  // Note that bix_count[0] should be blockcnt, [1] should be blockcnt - 1
  // and [2] should be blockcnt - 3
  // first block aborted erase
  int fs_size;
  if (magic[0] == (spiffs_obj_id)(-1) && bix_count[1] - bix_count[2] == 2) {
    fs_size = bix_count[1]+1;
  } else
  // second block aborted erase
  if (magic[1] == (spiffs_obj_id)(-1) && bix_count[0] - bix_count[2] == 3) {
    fs_size = bix_count[0];
  } else
  // third block aborted erase
  if (magic[2] == (spiffs_obj_id)(-1) && bix_count[0] - bix_count[1] == 1) {
    fs_size = bix_count[0];
  } else 
  // no block has aborted erase
  if (bix_count[0] - bix_count[1] == 1 && bix_count[1] - bix_count[2] == 2) {
    fs_size = bix_count[0];
  } else {
    return SPIFFS_ERR_PROBE_NOT_A_FS;
  }

  // check that we have sane number of blocks
  if (fs_size < 3) return SPIFFS_ERR_PROBE_TOO_FEW_BLOCKS;

  dummy_fs.block_count = fs_size;

  // Now verify that there is at least one good block at the end
  for (bix = fs_size - 1; bix >= 3; bix--) {
    spiffs_obj_id end_magic;
    paddr = SPIFFS_MAGIC_PADDR(&dummy_fs, bix);
#if SPIFFS_HAL_CALLBACK_EXTRA
    // not any proper fs to report here, so callback with null
    // (cross fingers that no-one gets angry)
    res = cfg->hal_read_f((void *)0, paddr, sizeof(spiffs_obj_id), (u8_t *)&end_magic);
#else
    res = cfg->hal_read_f(paddr, sizeof(spiffs_obj_id), (u8_t *)&end_magic);
#endif
    if (res < 0) {
      return SPIFFS_ERR_PROBE_NOT_A_FS;
    }
    if (end_magic == (spiffs_obj_id)(-1)) {
      if (bix < fs_size - 1) {
	return SPIFFS_ERR_PROBE_NOT_A_FS;
      }
    } else if (end_magic != SPIFFS_MAGIC(&dummy_fs, bix)) {
      return SPIFFS_ERR_PROBE_NOT_A_FS;
    } else {
      break;
    }
  }

  return fs_size * cfg->log_block_size;
}
#endif // SPIFFS_USE_MAGIC && SPIFFS_USE_MAGIC_LENGTH && SPIFFS_SINGLETON==0


static s32_t spiffs_obj_lu_scan_v(
    spiffs *fs,
    spiffs_obj_id obj_id,
    spiffs_block_ix bix,
    int ix_entry,
    const void *user_const_p,
    void *user_var_p) {
  (void)bix;
  (void)user_const_p;
  (void)user_var_p;
  if (obj_id == SPIFFS_OBJ_ID_FREE) {
    if (ix_entry == 0) {
      fs->free_blocks++;
      // todo optimize further, return SPIFFS_NEXT_BLOCK
    }
  } else if (obj_id == SPIFFS_OBJ_ID_DELETED) {
    fs->stats_p_deleted++;
  } else {
    fs->stats_p_allocated++;
  }

  return SPIFFS_VIS_COUNTINUE;
}


// Scans thru all obj lu and counts free, deleted and used pages
// Find the maximum block erase count
// Checks magic if enabled
s32_t spiffs_obj_lu_scan(
    spiffs *fs) {
  s32_t res;
  spiffs_block_ix bix;
  int entry;
#if SPIFFS_USE_MAGIC
  spiffs_block_ix unerased_bix = (spiffs_block_ix)-1;
#endif

  // find out erase count
  // if enabled, check magic
  bix = 0;
  spiffs_obj_id erase_count_final;
  spiffs_obj_id erase_count_min = SPIFFS_OBJ_ID_FREE;
  spiffs_obj_id erase_count_max = 0;
  while (bix < fs->block_count) {
#if SPIFFS_USE_MAGIC
    spiffs_obj_id magic;
    res = _spiffs_rd(fs,
        SPIFFS_OP_T_OBJ_LU2 | SPIFFS_OP_C_READ,
        0, SPIFFS_MAGIC_PADDR(fs, bix) ,
        sizeof(spiffs_obj_id), (u8_t *)&magic);

    SPIFFS_CHECK_RES(res);
    if (magic != SPIFFS_MAGIC(fs, bix)) {
      if (unerased_bix == (spiffs_block_ix)-1) {
        // allow one unerased block as it might be powered down during an erase
        unerased_bix = bix;
      } else {
        // more than one unerased block, bail out
        SPIFFS_CHECK_RES(SPIFFS_ERR_NOT_A_FS);
      }
    }
#endif
    spiffs_obj_id erase_count;
    res = _spiffs_rd(fs,
        SPIFFS_OP_T_OBJ_LU2 | SPIFFS_OP_C_READ,
        0, SPIFFS_ERASE_COUNT_PADDR(fs, bix) ,
        sizeof(spiffs_obj_id), (u8_t *)&erase_count);
    SPIFFS_CHECK_RES(res);
    if (erase_count != SPIFFS_OBJ_ID_FREE) {
      erase_count_min = MIN(erase_count_min, erase_count);
      erase_count_max = MAX(erase_count_max, erase_count);
    }
    bix++;
  }

  if (erase_count_min == 0 && erase_count_max == SPIFFS_OBJ_ID_FREE) {
    // clean system, set counter to zero
    erase_count_final = 0;
  } else if (erase_count_max - erase_count_min > (SPIFFS_OBJ_ID_FREE)/2) {
    // wrap, take min
    erase_count_final = erase_count_min+1;
  } else {
    erase_count_final = erase_count_max+1;
  }

  fs->max_erase_count = erase_count_final;

#if SPIFFS_USE_MAGIC
  if (unerased_bix != (spiffs_block_ix)-1) {
    // found one unerased block, remedy
    SPIFFS_DBG("mount: erase block %i\n", bix);
#if SPIFFS_READ_ONLY
    res = SPIFFS_ERR_RO_ABORTED_OPERATION;
#else
    res = spiffs_erase_block(fs, unerased_bix);
#endif // SPIFFS_READ_ONLY
    SPIFFS_CHECK_RES(res);
  }
#endif

  // count blocks

  fs->free_blocks = 0;
  fs->stats_p_allocated = 0;
  fs->stats_p_deleted = 0;

  res = spiffs_obj_lu_find_entry_visitor(fs,
      0,
      0,
      0,
      0,
      spiffs_obj_lu_scan_v,
      0,
      0,
      &bix,
      &entry);

  if (res == SPIFFS_VIS_END) {
    res = SPIFFS_OK;
  }

  SPIFFS_CHECK_RES(res);

  return res;
}

#if !SPIFFS_READ_ONLY
// Find free object lookup entry
// Iterate over object lookup pages in each block until a free object id entry is found
s32_t spiffs_obj_lu_find_free(
    spiffs *fs,
    spiffs_block_ix starting_block,
    int starting_lu_entry,
    spiffs_block_ix *block_ix,
    int *lu_entry) {
  s32_t res;
  if (!fs->cleaning && fs->free_blocks < 2) {
    res = spiffs_gc_quick(fs, 0);
    if (res == SPIFFS_ERR_NO_DELETED_BLOCKS) {
      res = SPIFFS_OK;
    }
    SPIFFS_CHECK_RES(res);
    if (fs->free_blocks < 2) {
      return SPIFFS_ERR_FULL;
    }
  }
  res = spiffs_obj_lu_find_id(fs, starting_block, starting_lu_entry,
      SPIFFS_OBJ_ID_FREE, block_ix, lu_entry);
  if (res == SPIFFS_OK) {
    fs->free_cursor_block_ix = *block_ix;
    fs->free_cursor_obj_lu_entry = *lu_entry;
    if (*lu_entry == 0) {
      fs->free_blocks--;
    }
  }
  if (res == SPIFFS_ERR_FULL) {
    SPIFFS_DBG("fs full\n");
  }

  return res;
}
#endif // !SPIFFS_READ_ONLY

// Find object lookup entry containing given id
// Iterate over object lookup pages in each block until a given object id entry is found
s32_t spiffs_obj_lu_find_id(
    spiffs *fs,
    spiffs_block_ix starting_block,
    int starting_lu_entry,
    spiffs_obj_id obj_id,
    spiffs_block_ix *block_ix,
    int *lu_entry) {
  s32_t res = spiffs_obj_lu_find_entry_visitor(
      fs, starting_block, starting_lu_entry, SPIFFS_VIS_CHECK_ID, obj_id, 0, 0, 0, block_ix, lu_entry);
  if (res == SPIFFS_VIS_END) {
    res = SPIFFS_ERR_NOT_FOUND;
  }
  return res;
}


static s32_t spiffs_obj_lu_find_id_and_span_v(
    spiffs *fs,
    spiffs_obj_id obj_id,
    spiffs_block_ix bix,
    int ix_entry,
    const void *user_const_p,
    void *user_var_p) {
  s32_t res;
  spiffs_page_header ph;
  spiffs_page_ix pix = SPIFFS_OBJ_LOOKUP_ENTRY_TO_PIX(fs, bix, ix_entry);
  res = _spiffs_rd(fs, 0, SPIFFS_OP_T_OBJ_LU2 | SPIFFS_OP_C_READ,
      SPIFFS_PAGE_TO_PADDR(fs, pix), sizeof(spiffs_page_header), (u8_t *)&ph);
  SPIFFS_CHECK_RES(res);
  if (ph.obj_id == obj_id &&
      ph.span_ix == *((spiffs_span_ix*)user_var_p) &&
      (ph.flags & (SPIFFS_PH_FLAG_FINAL | SPIFFS_PH_FLAG_DELET | SPIFFS_PH_FLAG_USED)) == SPIFFS_PH_FLAG_DELET &&
      !((obj_id & SPIFFS_OBJ_ID_IX_FLAG) && (ph.flags & SPIFFS_PH_FLAG_IXDELE) == 0 && ph.span_ix == 0) &&
      (user_const_p == 0 || *((const spiffs_page_ix*)user_const_p) != pix)) {
    return SPIFFS_OK;
  } else {
    return SPIFFS_VIS_COUNTINUE;
  }
}

// Find object lookup entry containing given id and span index
// Iterate over object lookup pages in each block until a given object id entry is found
s32_t spiffs_obj_lu_find_id_and_span(
    spiffs *fs,
    spiffs_obj_id obj_id,
    spiffs_span_ix spix,
    spiffs_page_ix exclusion_pix,
    spiffs_page_ix *pix) {
  s32_t res;
  spiffs_block_ix bix;
  int entry;

  res = spiffs_obj_lu_find_entry_visitor(fs,
      fs->cursor_block_ix,
      fs->cursor_obj_lu_entry,
      SPIFFS_VIS_CHECK_ID,
      obj_id,
      spiffs_obj_lu_find_id_and_span_v,
      exclusion_pix ? &exclusion_pix : 0,
      &spix,
      &bix,
      &entry);

  if (res == SPIFFS_VIS_END) {
    res = SPIFFS_ERR_NOT_FOUND;
  }

  SPIFFS_CHECK_RES(res);

  if (pix) {
    *pix = SPIFFS_OBJ_LOOKUP_ENTRY_TO_PIX(fs, bix, entry);
  }

  fs->cursor_block_ix = bix;
  fs->cursor_obj_lu_entry = entry;

  return res;
}

// Find object lookup entry containing given id and span index in page headers only
// Iterate over object lookup pages in each block until a given object id entry is found
s32_t spiffs_obj_lu_find_id_and_span_by_phdr(
    spiffs *fs,
    spiffs_obj_id obj_id,
    spiffs_span_ix spix,
    spiffs_page_ix exclusion_pix,
    spiffs_page_ix *pix) {
  s32_t res;
  spiffs_block_ix bix;
  int entry;

  res = spiffs_obj_lu_find_entry_visitor(fs,
      fs->cursor_block_ix,
      fs->cursor_obj_lu_entry,
      SPIFFS_VIS_CHECK_PH,
      obj_id,
      spiffs_obj_lu_find_id_and_span_v,
      exclusion_pix ? &exclusion_pix : 0,
      &spix,
      &bix,
      &entry);

  if (res == SPIFFS_VIS_END) {
    res = SPIFFS_ERR_NOT_FOUND;
  }

  SPIFFS_CHECK_RES(res);

  if (pix) {
    *pix = SPIFFS_OBJ_LOOKUP_ENTRY_TO_PIX(fs, bix, entry);
  }

  fs->cursor_block_ix = bix;
  fs->cursor_obj_lu_entry = entry;

  return res;
}

#if !SPIFFS_READ_ONLY
// Allocates a free defined page with given obj_id
// Occupies object lookup entry and page
// data may be NULL; where only page header is stored, len and page_offs is ignored
s32_t spiffs_page_allocate_data(
    spiffs *fs,
    spiffs_obj_id obj_id,
    spiffs_page_header *ph,
    u8_t *data,
    u32_t len,
    u32_t page_offs,
    u8_t finalize,
    spiffs_page_ix *pix) {
  s32_t res = SPIFFS_OK;
  spiffs_block_ix bix;
  int entry;

  // find free entry
  res = spiffs_obj_lu_find_free(fs, fs->free_cursor_block_ix, fs->free_cursor_obj_lu_entry, &bix, &entry);
  SPIFFS_CHECK_RES(res);

  // occupy page in object lookup
  res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_LU | SPIFFS_OP_C_UPDT,
      0, SPIFFS_BLOCK_TO_PADDR(fs, bix) + entry * sizeof(spiffs_obj_id), sizeof(spiffs_obj_id), (u8_t*)&obj_id);
  SPIFFS_CHECK_RES(res);

  fs->stats_p_allocated++;

  // write page header
  ph->flags &= ~SPIFFS_PH_FLAG_USED;
  res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_UPDT,
      0, SPIFFS_OBJ_LOOKUP_ENTRY_TO_PADDR(fs, bix, entry), sizeof(spiffs_page_header), (u8_t*)ph);
  SPIFFS_CHECK_RES(res);

  // write page data
  if (data) {
    res = _spiffs_wr(fs,  SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_UPDT,
        0,SPIFFS_OBJ_LOOKUP_ENTRY_TO_PADDR(fs, bix, entry) + sizeof(spiffs_page_header) + page_offs, len, data);
    SPIFFS_CHECK_RES(res);
  }

  // finalize header if necessary
  if (finalize && (ph->flags & SPIFFS_PH_FLAG_FINAL)) {
    ph->flags &= ~SPIFFS_PH_FLAG_FINAL;
    res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_UPDT,
        0, SPIFFS_OBJ_LOOKUP_ENTRY_TO_PADDR(fs, bix, entry) + offsetof(spiffs_page_header, flags),
        sizeof(u8_t),
        (u8_t *)&ph->flags);
    SPIFFS_CHECK_RES(res);
  }

  // return written page
  if (pix) {
    *pix = SPIFFS_OBJ_LOOKUP_ENTRY_TO_PIX(fs, bix, entry);
  }

  return res;
}
#endif // !SPIFFS_READ_ONLY

#if !SPIFFS_READ_ONLY
// Moves a page from src to a free page and finalizes it. Updates page index. Page data is given in param page.
// If page data is null, provided header is used for metainfo and page data is physically copied.
s32_t spiffs_page_move(
    spiffs *fs,
    spiffs_file fh,
    u8_t *page_data,
    spiffs_obj_id obj_id,
    spiffs_page_header *page_hdr,
    spiffs_page_ix src_pix,
    spiffs_page_ix *dst_pix) {
  s32_t res;
  u8_t was_final = 0;
  spiffs_page_header *p_hdr;
  spiffs_block_ix bix;
  int entry;
  spiffs_page_ix free_pix;

  // find free entry
  res = spiffs_obj_lu_find_free(fs, fs->free_cursor_block_ix, fs->free_cursor_obj_lu_entry, &bix, &entry);
  SPIFFS_CHECK_RES(res);
  free_pix = SPIFFS_OBJ_LOOKUP_ENTRY_TO_PIX(fs, bix, entry);

  if (dst_pix) *dst_pix = free_pix;

  p_hdr = page_data ? (spiffs_page_header *)page_data : page_hdr;
  if (page_data) {
    // got page data
    was_final = (p_hdr->flags & SPIFFS_PH_FLAG_FINAL) == 0;
    // write unfinalized page
    p_hdr->flags |= SPIFFS_PH_FLAG_FINAL;
    p_hdr->flags &= ~SPIFFS_PH_FLAG_USED;
    res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_UPDT,
        0, SPIFFS_PAGE_TO_PADDR(fs, free_pix), SPIFFS_CFG_LOG_PAGE_SZ(fs), page_data);
  } else {
    // copy page data
    res = spiffs_phys_cpy(fs, fh, SPIFFS_PAGE_TO_PADDR(fs, free_pix), SPIFFS_PAGE_TO_PADDR(fs, src_pix), SPIFFS_CFG_LOG_PAGE_SZ(fs));
  }
  SPIFFS_CHECK_RES(res);

  // mark entry in destination object lookup
  res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_LU | SPIFFS_OP_C_UPDT,
      0, SPIFFS_BLOCK_TO_PADDR(fs, SPIFFS_BLOCK_FOR_PAGE(fs, free_pix)) + SPIFFS_OBJ_LOOKUP_ENTRY_FOR_PAGE(fs, free_pix) * sizeof(spiffs_page_ix),
      sizeof(spiffs_obj_id),
      (u8_t *)&obj_id);
  SPIFFS_CHECK_RES(res);

  fs->stats_p_allocated++;

  if (was_final) {
    // mark finalized in destination page
    p_hdr->flags &= ~(SPIFFS_PH_FLAG_FINAL | SPIFFS_PH_FLAG_USED);
    res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_UPDT,
        fh,
        SPIFFS_PAGE_TO_PADDR(fs, free_pix) + offsetof(spiffs_page_header, flags),
        sizeof(u8_t),
        (u8_t *)&p_hdr->flags);
    SPIFFS_CHECK_RES(res);
  }
  // mark source deleted
  res = spiffs_page_delete(fs, src_pix);
  return res;
}
#endif // !SPIFFS_READ_ONLY

#if !SPIFFS_READ_ONLY
// Deletes a page and removes it from object lookup.
s32_t spiffs_page_delete(
    spiffs *fs,
    spiffs_page_ix pix) {
  s32_t res;
  spiffs_page_header hdr;
  hdr.flags = 0xff & ~(SPIFFS_PH_FLAG_DELET | SPIFFS_PH_FLAG_USED);
  // mark deleted entry in source object lookup
  spiffs_obj_id d_obj_id = SPIFFS_OBJ_ID_DELETED;
  res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_LU | SPIFFS_OP_C_DELE,
      0,
      SPIFFS_BLOCK_TO_PADDR(fs, SPIFFS_BLOCK_FOR_PAGE(fs, pix)) + SPIFFS_OBJ_LOOKUP_ENTRY_FOR_PAGE(fs, pix) * sizeof(spiffs_page_ix),
      sizeof(spiffs_obj_id),
      (u8_t *)&d_obj_id);
  SPIFFS_CHECK_RES(res);

  fs->stats_p_deleted++;
  fs->stats_p_allocated--;

  // mark deleted in source page
  res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_DELE,
      0,
      SPIFFS_PAGE_TO_PADDR(fs, pix) + offsetof(spiffs_page_header, flags),
      sizeof(u8_t),
      (u8_t *)&hdr.flags);

  return res;
}
#endif // !SPIFFS_READ_ONLY

#if !SPIFFS_READ_ONLY
// Create an object index header page with empty index and undefined length
s32_t spiffs_object_create(
    spiffs *fs,
    spiffs_obj_id obj_id,
    const u8_t name[SPIFFS_OBJ_NAME_LEN],
    spiffs_obj_type type,
    spiffs_page_ix *objix_hdr_pix) {
  s32_t res = SPIFFS_OK;
  spiffs_block_ix bix;
  spiffs_page_object_ix_header oix_hdr;
  int entry;

  res = spiffs_gc_check(fs, SPIFFS_DATA_PAGE_SIZE(fs));
  SPIFFS_CHECK_RES(res);

  obj_id |= SPIFFS_OBJ_ID_IX_FLAG;

  // find free entry
  res = spiffs_obj_lu_find_free(fs, fs->free_cursor_block_ix, fs->free_cursor_obj_lu_entry, &bix, &entry);
  SPIFFS_CHECK_RES(res);
  SPIFFS_DBG("create: found free page @ %04x bix:%i entry:%i\n", SPIFFS_OBJ_LOOKUP_ENTRY_TO_PIX(fs, bix, entry), bix, entry);

  // occupy page in object lookup
  res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_LU | SPIFFS_OP_C_UPDT,
      0, SPIFFS_BLOCK_TO_PADDR(fs, bix) + entry * sizeof(spiffs_obj_id), sizeof(spiffs_obj_id), (u8_t*)&obj_id);
  SPIFFS_CHECK_RES(res);

  fs->stats_p_allocated++;

  // write empty object index page
  oix_hdr.p_hdr.obj_id = obj_id;
  oix_hdr.p_hdr.span_ix = 0;
  oix_hdr.p_hdr.flags = 0xff & ~(SPIFFS_PH_FLAG_FINAL | SPIFFS_PH_FLAG_INDEX | SPIFFS_PH_FLAG_USED);
  oix_hdr.type = type;
  oix_hdr.size = SPIFFS_UNDEFINED_LEN; // keep ones so we can update later without wasting this page
  strncpy((char*)&oix_hdr.name, (const char*)name, SPIFFS_OBJ_NAME_LEN);


  // update page
  res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_UPDT,
      0, SPIFFS_OBJ_LOOKUP_ENTRY_TO_PADDR(fs, bix, entry), sizeof(spiffs_page_object_ix_header), (u8_t*)&oix_hdr);

  SPIFFS_CHECK_RES(res);
  spiffs_cb_object_event(fs, 0, SPIFFS_EV_IX_NEW, obj_id, 0, SPIFFS_OBJ_LOOKUP_ENTRY_TO_PIX(fs, bix, entry), SPIFFS_UNDEFINED_LEN);

  if (objix_hdr_pix) {
    *objix_hdr_pix = SPIFFS_OBJ_LOOKUP_ENTRY_TO_PIX(fs, bix, entry);
  }

  return res;
}
#endif // !SPIFFS_READ_ONLY

#if !SPIFFS_READ_ONLY
// update object index header with any combination of name/size/index
// new_objix_hdr_data may be null, if so the object index header page is loaded
// name may be null, if so name is not changed
// size may be null, if so size is not changed
s32_t spiffs_object_update_index_hdr(
    spiffs *fs,
    spiffs_fd *fd,
    spiffs_obj_id obj_id,
    spiffs_page_ix objix_hdr_pix,
    u8_t *new_objix_hdr_data,
    const u8_t name[SPIFFS_OBJ_NAME_LEN],
    u32_t size,
    spiffs_page_ix *new_pix) {
  s32_t res = SPIFFS_OK;
  spiffs_page_object_ix_header *objix_hdr;
  spiffs_page_ix new_objix_hdr_pix;

  obj_id |=  SPIFFS_OBJ_ID_IX_FLAG;

  if (new_objix_hdr_data) {
    // object index header page already given to us, no need to load it
    objix_hdr = (spiffs_page_object_ix_header *)new_objix_hdr_data;
  } else {
    // read object index header page
    res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_IX | SPIFFS_OP_C_READ,
        fd->file_nbr, SPIFFS_PAGE_TO_PADDR(fs, objix_hdr_pix), SPIFFS_CFG_LOG_PAGE_SZ(fs), fs->work);
    SPIFFS_CHECK_RES(res);
    objix_hdr = (spiffs_page_object_ix_header *)fs->work;
  }

  SPIFFS_VALIDATE_OBJIX(objix_hdr->p_hdr, obj_id, 0);

  // change name
  if (name) {
    strncpy((char*)objix_hdr->name, (const char*)name, SPIFFS_OBJ_NAME_LEN);
  }
  if (size) {
    objix_hdr->size = size;
  }

  // move and update page
  res = spiffs_page_move(fs, fd == 0 ? 0 : fd->file_nbr, (u8_t*)objix_hdr, obj_id, 0, objix_hdr_pix, &new_objix_hdr_pix);

  if (res == SPIFFS_OK) {
    if (new_pix) {
      *new_pix = new_objix_hdr_pix;
    }
    // callback on object index update
    spiffs_cb_object_event(fs, fd, SPIFFS_EV_IX_UPD, obj_id, objix_hdr->p_hdr.span_ix, new_objix_hdr_pix, objix_hdr->size);
    if (fd) fd->objix_hdr_pix = new_objix_hdr_pix; // if this is not in the registered cluster
  }

  return res;
}
#endif // !SPIFFS_READ_ONLY

void spiffs_cb_object_event(
    spiffs *fs,
    spiffs_fd *fd,
    int ev,
    spiffs_obj_id obj_id_raw,
    spiffs_span_ix spix,
    spiffs_page_ix new_pix,
    u32_t new_size) {
  (void)fd;
  // update index caches in all file descriptors
  spiffs_obj_id obj_id = obj_id_raw & ~SPIFFS_OBJ_ID_IX_FLAG;
  u32_t i;
  spiffs_fd *fds = (spiffs_fd *)fs->fd_space;
  for (i = 0; i < fs->fd_count; i++) {
    spiffs_fd *cur_fd = &fds[i];
    if (cur_fd->file_nbr == 0 || (cur_fd->obj_id & ~SPIFFS_OBJ_ID_IX_FLAG) != obj_id) continue;
    if (spix == 0) {
      if (ev == SPIFFS_EV_IX_NEW || ev == SPIFFS_EV_IX_UPD) {
        SPIFFS_DBG("       callback: setting fd %i:%04x objix_hdr_pix to %04x, size:%i\n", cur_fd->file_nbr, cur_fd->obj_id, new_pix, new_size);
        cur_fd->objix_hdr_pix = new_pix;
        if (new_size != 0) {
          cur_fd->size = new_size;
        }
      } else if (ev == SPIFFS_EV_IX_DEL) {
        cur_fd->file_nbr = 0;
        cur_fd->obj_id = SPIFFS_OBJ_ID_DELETED;
      }
    }
    if (cur_fd->cursor_objix_spix == spix) {
      if (ev == SPIFFS_EV_IX_NEW || ev == SPIFFS_EV_IX_UPD) {
        SPIFFS_DBG("       callback: setting fd %i:%04x span:%04x objix_pix to %04x\n", cur_fd->file_nbr, cur_fd->obj_id, spix, new_pix);
        cur_fd->cursor_objix_pix = new_pix;
      } else {
        cur_fd->cursor_objix_pix = 0;
      }
    }
  }

  // callback to user if object index header
  if (fs->file_cb_f && spix == 0 && (obj_id_raw & SPIFFS_OBJ_ID_IX_FLAG)) {
    spiffs_fileop_type op;
    if (ev == SPIFFS_EV_IX_NEW) {
      op = SPIFFS_CB_CREATED;
    } else if (ev == SPIFFS_EV_IX_UPD) {
      op = SPIFFS_CB_UPDATED;
    } else if (ev == SPIFFS_EV_IX_DEL) {
      op = SPIFFS_CB_DELETED;
    } else {
      SPIFFS_DBG("       callback: WARNING unknown callback event %02x\n", ev);
      return; // bail out
    }
    fs->file_cb_f(fs, op, obj_id, new_pix);
  }
}

// Open object by id
s32_t spiffs_object_open_by_id(
    spiffs *fs,
    spiffs_obj_id obj_id,
    spiffs_fd *fd,
    spiffs_flags flags,
    spiffs_mode mode) {
  s32_t res = SPIFFS_OK;
  spiffs_page_ix pix;

  res = spiffs_obj_lu_find_id_and_span(fs, obj_id | SPIFFS_OBJ_ID_IX_FLAG, 0, 0, &pix);
  SPIFFS_CHECK_RES(res);

  res = spiffs_object_open_by_page(fs, pix, fd, flags, mode);

  return res;
}

// Open object by page index
s32_t spiffs_object_open_by_page(
    spiffs *fs,
    spiffs_page_ix pix,
    spiffs_fd *fd,
    spiffs_flags flags,
    spiffs_mode mode) {
  (void)mode;
  s32_t res = SPIFFS_OK;
  spiffs_page_object_ix_header oix_hdr;
  spiffs_obj_id obj_id;

  res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_IX | SPIFFS_OP_C_READ,
      fd->file_nbr, SPIFFS_PAGE_TO_PADDR(fs, pix), sizeof(spiffs_page_object_ix_header), (u8_t *)&oix_hdr);
  SPIFFS_CHECK_RES(res);

  spiffs_block_ix bix = SPIFFS_BLOCK_FOR_PAGE(fs, pix);
  int entry = SPIFFS_OBJ_LOOKUP_ENTRY_FOR_PAGE(fs, pix);

  res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_LU | SPIFFS_OP_C_READ,
      0,  SPIFFS_BLOCK_TO_PADDR(fs, bix) + entry * sizeof(spiffs_obj_id), sizeof(spiffs_obj_id), (u8_t *)&obj_id);

  fd->fs = fs;
  fd->objix_hdr_pix = pix;
  fd->size = oix_hdr.size;
  fd->offset = 0;
  fd->cursor_objix_pix = pix;
  fd->cursor_objix_spix = 0;
  fd->obj_id = obj_id;
  fd->flags = flags;

  SPIFFS_VALIDATE_OBJIX(oix_hdr.p_hdr, fd->obj_id, 0);

  SPIFFS_DBG("open: fd %i is obj id %04x\n", fd->file_nbr, fd->obj_id);

  return res;
}

#if !SPIFFS_READ_ONLY
// Append to object
// keep current object index (header) page in fs->work buffer
s32_t spiffs_object_append(spiffs_fd *fd, u32_t offset, u8_t *data, u32_t len) {
  spiffs *fs = fd->fs;
  s32_t res = SPIFFS_OK;
  u32_t written = 0;

  SPIFFS_DBG("append: %i bytes @ offs %i of size %i\n", len, offset, fd->size);

  if (offset > fd->size) {
    SPIFFS_DBG("append: offset reversed to size\n");
    offset = fd->size;
  }

  res = spiffs_gc_check(fs, len + SPIFFS_DATA_PAGE_SIZE(fs)); // add an extra page of data worth for meta
  if (res != SPIFFS_OK) {
    SPIFFS_DBG("append: gc check fail %i\n", res);
  }
  SPIFFS_CHECK_RES(res);

  spiffs_page_object_ix_header *objix_hdr = (spiffs_page_object_ix_header *)fs->work;
  spiffs_page_object_ix *objix = (spiffs_page_object_ix *)fs->work;
  spiffs_page_header p_hdr;

  spiffs_span_ix cur_objix_spix = 0;
  spiffs_span_ix prev_objix_spix = (spiffs_span_ix)-1;
  spiffs_page_ix cur_objix_pix = fd->objix_hdr_pix;
  spiffs_page_ix new_objix_hdr_page;

  spiffs_span_ix data_spix = offset / SPIFFS_DATA_PAGE_SIZE(fs);
  spiffs_page_ix data_page;
  u32_t page_offs = offset % SPIFFS_DATA_PAGE_SIZE(fs);

  // write all data
  while (res == SPIFFS_OK && written < len) {
    // calculate object index page span index
    cur_objix_spix = SPIFFS_OBJ_IX_ENTRY_SPAN_IX(fs, data_spix);

    // handle storing and loading of object indices
    if (cur_objix_spix != prev_objix_spix) {
      // new object index page
      // within this clause we return directly if something fails, object index mess-up
      if (written > 0) {
        // store previous object index page, unless first pass
        SPIFFS_DBG("append: %04x store objix %04x:%04x, written %i\n", fd->obj_id,
            cur_objix_pix, prev_objix_spix, written);
        if (prev_objix_spix == 0) {
          // this is an update to object index header page
          objix_hdr->size = offset+written;
          if (offset == 0) {
            // was an empty object, update same page (size was 0xffffffff)
            res = spiffs_page_index_check(fs, fd, cur_objix_pix, 0);
            SPIFFS_CHECK_RES(res);
            res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_IX | SPIFFS_OP_C_UPDT,
                fd->file_nbr, SPIFFS_PAGE_TO_PADDR(fs, cur_objix_pix), SPIFFS_CFG_LOG_PAGE_SZ(fs), fs->work);
            SPIFFS_CHECK_RES(res);
          } else {
            // was a nonempty object, update to new page
            res = spiffs_object_update_index_hdr(fs, fd, fd->obj_id,
                fd->objix_hdr_pix, fs->work, 0, offset+written, &new_objix_hdr_page);
            SPIFFS_CHECK_RES(res);
            SPIFFS_DBG("append: %04x store new objix_hdr, %04x:%04x, written %i\n", fd->obj_id,
                new_objix_hdr_page, 0, written);
          }
        } else {
          // this is an update to an object index page
          res = spiffs_page_index_check(fs, fd, cur_objix_pix, prev_objix_spix);
          SPIFFS_CHECK_RES(res);

          res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_IX | SPIFFS_OP_C_UPDT,
              fd->file_nbr, SPIFFS_PAGE_TO_PADDR(fs, cur_objix_pix), SPIFFS_CFG_LOG_PAGE_SZ(fs), fs->work);
          SPIFFS_CHECK_RES(res);
          spiffs_cb_object_event(fs, fd, SPIFFS_EV_IX_UPD,fd->obj_id, objix->p_hdr.span_ix, cur_objix_pix, 0);
          // update length in object index header page
          res = spiffs_object_update_index_hdr(fs, fd, fd->obj_id,
              fd->objix_hdr_pix, 0, 0, offset+written, &new_objix_hdr_page);
          SPIFFS_CHECK_RES(res);
          SPIFFS_DBG("append: %04x store new size I %i in objix_hdr, %04x:%04x, written %i\n", fd->obj_id,
              offset+written, new_objix_hdr_page, 0, written);
        }
        fd->size = offset+written;
        fd->offset = offset+written;
      }

      // create or load new object index page
      if (cur_objix_spix == 0) {
        // load object index header page, must always exist
        SPIFFS_DBG("append: %04x load objixhdr page %04x:%04x\n", fd->obj_id, cur_objix_pix, cur_objix_spix);
        res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_IX | SPIFFS_OP_C_READ,
            fd->file_nbr, SPIFFS_PAGE_TO_PADDR(fs, cur_objix_pix), SPIFFS_CFG_LOG_PAGE_SZ(fs), fs->work);
        SPIFFS_CHECK_RES(res);
        SPIFFS_VALIDATE_OBJIX(objix_hdr->p_hdr, fd->obj_id, cur_objix_spix);
      } else {
        spiffs_span_ix len_objix_spix = SPIFFS_OBJ_IX_ENTRY_SPAN_IX(fs, (fd->size-1)/SPIFFS_DATA_PAGE_SIZE(fs));
        // on subsequent passes, create a new object index page
        if (written > 0 || cur_objix_spix > len_objix_spix) {
          p_hdr.obj_id = fd->obj_id | SPIFFS_OBJ_ID_IX_FLAG;
          p_hdr.span_ix = cur_objix_spix;
          p_hdr.flags = 0xff & ~(SPIFFS_PH_FLAG_FINAL | SPIFFS_PH_FLAG_INDEX);
          res = spiffs_page_allocate_data(fs, fd->obj_id | SPIFFS_OBJ_ID_IX_FLAG,
              &p_hdr, 0, 0, 0, 1, &cur_objix_pix);
          SPIFFS_CHECK_RES(res);
          spiffs_cb_object_event(fs, fd, SPIFFS_EV_IX_NEW, fd->obj_id, cur_objix_spix, cur_objix_pix, 0);
          // quick "load" of new object index page
          memset(fs->work, 0xff, SPIFFS_CFG_LOG_PAGE_SZ(fs));
          memcpy(fs->work, &p_hdr, sizeof(spiffs_page_header));
          SPIFFS_DBG("append: %04x create objix page, %04x:%04x, written %i\n", fd->obj_id
              , cur_objix_pix, cur_objix_spix, written);
        } else {
          // on first pass, we load existing object index page
          spiffs_page_ix pix;
          SPIFFS_DBG("append: %04x find objix span_ix:%04x\n", fd->obj_id, cur_objix_spix);
          if (fd->cursor_objix_spix == cur_objix_spix) {
            pix = fd->cursor_objix_pix;
          } else {
            res = spiffs_obj_lu_find_id_and_span(fs, fd->obj_id | SPIFFS_OBJ_ID_IX_FLAG, cur_objix_spix, 0, &pix);
            SPIFFS_CHECK_RES(res);
          }
          SPIFFS_DBG("append: %04x found object index at page %04x [fd size %i]\n", fd->obj_id, pix, fd->size);
          res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_IX | SPIFFS_OP_C_READ,
              fd->file_nbr, SPIFFS_PAGE_TO_PADDR(fs, pix), SPIFFS_CFG_LOG_PAGE_SZ(fs), fs->work);
          SPIFFS_CHECK_RES(res);
          SPIFFS_VALIDATE_OBJIX(objix_hdr->p_hdr, fd->obj_id, cur_objix_spix);
          cur_objix_pix = pix;
        }
        fd->cursor_objix_pix = cur_objix_pix;
        fd->cursor_objix_spix = cur_objix_spix;
        fd->offset = offset+written;
        fd->size = offset+written;
      }
      prev_objix_spix = cur_objix_spix;
    }

    // write data
    u32_t to_write = MIN(len-written, SPIFFS_DATA_PAGE_SIZE(fs) - page_offs);
    if (page_offs == 0) {
      // at beginning of a page, allocate and write a new page of data
      p_hdr.obj_id = fd->obj_id & ~SPIFFS_OBJ_ID_IX_FLAG;
      p_hdr.span_ix = data_spix;
      p_hdr.flags = 0xff & ~(SPIFFS_PH_FLAG_FINAL);  // finalize immediately
      res = spiffs_page_allocate_data(fs, fd->obj_id & ~SPIFFS_OBJ_ID_IX_FLAG,
          &p_hdr, &data[written], to_write, page_offs, 1, &data_page);
      SPIFFS_DBG("append: %04x store new data page, %04x:%04x offset:%i, len %i, written %i\n", fd->obj_id,
          data_page, data_spix, page_offs, to_write, written);
    } else {
      // append to existing page, fill out free data in existing page
      if (cur_objix_spix == 0) {
        // get data page from object index header page
        data_page = ((spiffs_page_ix*)((u8_t *)objix_hdr + sizeof(spiffs_page_object_ix_header)))[data_spix];
      } else {
        // get data page from object index page
        data_page = ((spiffs_page_ix*)((u8_t *)objix + sizeof(spiffs_page_object_ix)))[SPIFFS_OBJ_IX_ENTRY(fs, data_spix)];
      }

      res = spiffs_page_data_check(fs, fd, data_page, data_spix);
      SPIFFS_CHECK_RES(res);

      res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_UPDT,
          fd->file_nbr, SPIFFS_PAGE_TO_PADDR(fs, data_page) + sizeof(spiffs_page_header) + page_offs, to_write, &data[written]);
      SPIFFS_DBG("append: %04x store to existing data page, %04x:%04x offset:%i, len %i, written %i\n", fd->obj_id
          , data_page, data_spix, page_offs, to_write, written);
    }

    if (res != SPIFFS_OK) break;

    // update memory representation of object index page with new data page
    if (cur_objix_spix == 0) {
      // update object index header page
      ((spiffs_page_ix*)((u8_t *)objix_hdr + sizeof(spiffs_page_object_ix_header)))[data_spix] = data_page;
      SPIFFS_DBG("append: %04x wrote page %04x to objix_hdr entry %02x in mem\n", fd->obj_id
          , data_page, data_spix);
      objix_hdr->size = offset+written;
    } else {
      // update object index page
      ((spiffs_page_ix*)((u8_t *)objix + sizeof(spiffs_page_object_ix)))[SPIFFS_OBJ_IX_ENTRY(fs, data_spix)] = data_page;
      SPIFFS_DBG("append: %04x wrote page %04x to objix entry %02x in mem\n", fd->obj_id
          , data_page, SPIFFS_OBJ_IX_ENTRY(fs, data_spix));
    }

    // update internals
    page_offs = 0;
    data_spix++;
    written += to_write;
  } // while all data

  fd->size = offset+written;
  fd->offset = offset+written;
  fd->cursor_objix_pix = cur_objix_pix;
  fd->cursor_objix_spix = cur_objix_spix;

  // finalize updated object indices
  s32_t res2 = SPIFFS_OK;
  if (cur_objix_spix != 0) {
    // wrote beyond object index header page
    // write last modified object index page, unless object header index page
    SPIFFS_DBG("append: %04x store objix page, %04x:%04x, written %i\n", fd->obj_id,
        cur_objix_pix, cur_objix_spix, written);

    res2 = spiffs_page_index_check(fs, fd, cur_objix_pix, cur_objix_spix);
    SPIFFS_CHECK_RES(res2);

    res2 = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_IX | SPIFFS_OP_C_UPDT,
        fd->file_nbr, SPIFFS_PAGE_TO_PADDR(fs, cur_objix_pix), SPIFFS_CFG_LOG_PAGE_SZ(fs), fs->work);
    SPIFFS_CHECK_RES(res2);
    spiffs_cb_object_event(fs, fd, SPIFFS_EV_IX_UPD, fd->obj_id, objix->p_hdr.span_ix, cur_objix_pix, 0);

    // update size in object header index page
    res2 = spiffs_object_update_index_hdr(fs, fd, fd->obj_id,
        fd->objix_hdr_pix, 0, 0, offset+written, &new_objix_hdr_page);
    SPIFFS_DBG("append: %04x store new size II %i in objix_hdr, %04x:%04x, written %i, res %i\n", fd->obj_id
        , offset+written, new_objix_hdr_page, 0, written, res2);
    SPIFFS_CHECK_RES(res2);
  } else {
    // wrote within object index header page
    if (offset == 0) {
      // wrote to empty object - simply update size and write whole page
      objix_hdr->size = offset+written;
      SPIFFS_DBG("append: %04x store fresh objix_hdr page, %04x:%04x, written %i\n", fd->obj_id
          , cur_objix_pix, cur_objix_spix, written);

      res2 = spiffs_page_index_check(fs, fd, cur_objix_pix, cur_objix_spix);
      SPIFFS_CHECK_RES(res2);

      res2 = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_IX | SPIFFS_OP_C_UPDT,
          fd->file_nbr, SPIFFS_PAGE_TO_PADDR(fs, cur_objix_pix), SPIFFS_CFG_LOG_PAGE_SZ(fs), fs->work);
      SPIFFS_CHECK_RES(res2);
      // callback on object index update
      spiffs_cb_object_event(fs, fd, SPIFFS_EV_IX_UPD, fd->obj_id, objix_hdr->p_hdr.span_ix, cur_objix_pix, objix_hdr->size);
    } else {
      // modifying object index header page, update size and make new copy
      res2 = spiffs_object_update_index_hdr(fs, fd, fd->obj_id,
          fd->objix_hdr_pix, fs->work, 0, offset+written, &new_objix_hdr_page);
      SPIFFS_DBG("append: %04x store modified objix_hdr page, %04x:%04x, written %i\n", fd->obj_id
          , new_objix_hdr_page, 0, written);
      SPIFFS_CHECK_RES(res2);
    }
  }

  return res;
} // spiffs_object_append
#endif // !SPIFFS_READ_ONLY

#if !SPIFFS_READ_ONLY
// Modify object
// keep current object index (header) page in fs->work buffer
s32_t spiffs_object_modify(spiffs_fd *fd, u32_t offset, u8_t *data, u32_t len) {
  spiffs *fs = fd->fs;
  s32_t res = SPIFFS_OK;
  u32_t written = 0;

  res = spiffs_gc_check(fs, len + SPIFFS_DATA_PAGE_SIZE(fs));
  SPIFFS_CHECK_RES(res);

  spiffs_page_object_ix_header *objix_hdr = (spiffs_page_object_ix_header *)fs->work;
  spiffs_page_object_ix *objix = (spiffs_page_object_ix *)fs->work;
  spiffs_page_header p_hdr;

  spiffs_span_ix cur_objix_spix = 0;
  spiffs_span_ix prev_objix_spix = (spiffs_span_ix)-1;
  spiffs_page_ix cur_objix_pix = fd->objix_hdr_pix;
  spiffs_page_ix new_objix_hdr_pix;

  spiffs_span_ix data_spix = offset / SPIFFS_DATA_PAGE_SIZE(fs);
  spiffs_page_ix data_pix;
  u32_t page_offs = offset % SPIFFS_DATA_PAGE_SIZE(fs);


  // write all data
  while (res == SPIFFS_OK && written < len) {
    // calculate object index page span index
    cur_objix_spix = SPIFFS_OBJ_IX_ENTRY_SPAN_IX(fs, data_spix);

    // handle storing and loading of object indices
    if (cur_objix_spix != prev_objix_spix) {
      // new object index page
      // within this clause we return directly if something fails, object index mess-up
      if (written > 0) {
        // store previous object index (header) page, unless first pass
        if (prev_objix_spix == 0) {
          // store previous object index header page
          res = spiffs_object_update_index_hdr(fs, fd, fd->obj_id,
              fd->objix_hdr_pix, fs->work, 0, 0, &new_objix_hdr_pix);
          SPIFFS_DBG("modify: store modified objix_hdr page, %04x:%04x, written %i\n", new_objix_hdr_pix, 0, written);
          SPIFFS_CHECK_RES(res);
        } else {
          // store new version of previous object index page
          spiffs_page_ix new_objix_pix;

          res = spiffs_page_index_check(fs, fd, cur_objix_pix, prev_objix_spix);
          SPIFFS_CHECK_RES(res);

          res = spiffs_page_move(fs, fd->file_nbr, (u8_t*)objix, fd->obj_id, 0, cur_objix_pix, &new_objix_pix);
          SPIFFS_DBG("modify: store previous modified objix page, %04x:%04x, written %i\n", new_objix_pix, objix->p_hdr.span_ix, written);
          SPIFFS_CHECK_RES(res);
          spiffs_cb_object_event(fs, fd, SPIFFS_EV_IX_UPD, fd->obj_id, objix->p_hdr.span_ix, new_objix_pix, 0);
        }
      }

      // load next object index page
      if (cur_objix_spix == 0) {
        // load object index header page, must exist
        SPIFFS_DBG("modify: load objixhdr page %04x:%04x\n", cur_objix_pix, cur_objix_spix);
        res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_IX | SPIFFS_OP_C_READ,
            fd->file_nbr, SPIFFS_PAGE_TO_PADDR(fs, cur_objix_pix), SPIFFS_CFG_LOG_PAGE_SZ(fs), fs->work);
        SPIFFS_CHECK_RES(res);
        SPIFFS_VALIDATE_OBJIX(objix_hdr->p_hdr, fd->obj_id, cur_objix_spix);
      } else {
        // load existing object index page on first pass
        spiffs_page_ix pix;
        SPIFFS_DBG("modify: find objix span_ix:%04x\n", cur_objix_spix);
        if (fd->cursor_objix_spix == cur_objix_spix) {
          pix = fd->cursor_objix_pix;
        } else {
          res = spiffs_obj_lu_find_id_and_span(fs, fd->obj_id | SPIFFS_OBJ_ID_IX_FLAG, cur_objix_spix, 0, &pix);
          SPIFFS_CHECK_RES(res);
        }
        SPIFFS_DBG("modify: found object index at page %04x\n", pix);
        res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_IX | SPIFFS_OP_C_READ,
            fd->file_nbr, SPIFFS_PAGE_TO_PADDR(fs, pix), SPIFFS_CFG_LOG_PAGE_SZ(fs), fs->work);
        SPIFFS_CHECK_RES(res);
        SPIFFS_VALIDATE_OBJIX(objix_hdr->p_hdr, fd->obj_id, cur_objix_spix);
        cur_objix_pix = pix;
      }
      fd->cursor_objix_pix = cur_objix_pix;
      fd->cursor_objix_spix = cur_objix_spix;
      fd->offset = offset+written;
      prev_objix_spix = cur_objix_spix;
    }

    // write partial data
    u32_t to_write = MIN(len-written, SPIFFS_DATA_PAGE_SIZE(fs) - page_offs);
    spiffs_page_ix orig_data_pix;
    if (cur_objix_spix == 0) {
      // get data page from object index header page
      orig_data_pix = ((spiffs_page_ix*)((u8_t *)objix_hdr + sizeof(spiffs_page_object_ix_header)))[data_spix];
    } else {
      // get data page from object index page
      orig_data_pix = ((spiffs_page_ix*)((u8_t *)objix + sizeof(spiffs_page_object_ix)))[SPIFFS_OBJ_IX_ENTRY(fs, data_spix)];
    }

    p_hdr.obj_id = fd->obj_id & ~SPIFFS_OBJ_ID_IX_FLAG;
    p_hdr.span_ix = data_spix;
    p_hdr.flags = 0xff;
    if (page_offs == 0 && to_write == SPIFFS_DATA_PAGE_SIZE(fs)) {
      // a full page, allocate and write a new page of data
      res = spiffs_page_allocate_data(fs, fd->obj_id & ~SPIFFS_OBJ_ID_IX_FLAG,
          &p_hdr, &data[written], to_write, page_offs, 1, &data_pix);
      SPIFFS_DBG("modify: store new data page, %04x:%04x offset:%i, len %i, written %i\n", data_pix, data_spix, page_offs, to_write, written);
    } else {
      // write to existing page, allocate new and copy unmodified data

      res = spiffs_page_data_check(fs, fd, orig_data_pix, data_spix);
      SPIFFS_CHECK_RES(res);

      res = spiffs_page_allocate_data(fs, fd->obj_id & ~SPIFFS_OBJ_ID_IX_FLAG,
          &p_hdr, 0, 0, 0, 0, &data_pix);
      if (res != SPIFFS_OK) break;

      // copy unmodified data
      if (page_offs > 0) {
        // before modification
        res = spiffs_phys_cpy(fs, fd->file_nbr,
            SPIFFS_PAGE_TO_PADDR(fs, data_pix) + sizeof(spiffs_page_header),
            SPIFFS_PAGE_TO_PADDR(fs, orig_data_pix) + sizeof(spiffs_page_header),
            page_offs);
        if (res != SPIFFS_OK) break;
      }
      if (page_offs + to_write < SPIFFS_DATA_PAGE_SIZE(fs)) {
        // after modification
        res = spiffs_phys_cpy(fs, fd->file_nbr,
            SPIFFS_PAGE_TO_PADDR(fs, data_pix) + sizeof(spiffs_page_header) + page_offs + to_write,
            SPIFFS_PAGE_TO_PADDR(fs, orig_data_pix) + sizeof(spiffs_page_header) + page_offs + to_write,
            SPIFFS_DATA_PAGE_SIZE(fs) - (page_offs + to_write));
        if (res != SPIFFS_OK) break;
      }

      res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_UPDT,
          fd->file_nbr,
          SPIFFS_PAGE_TO_PADDR(fs, data_pix) + sizeof(spiffs_page_header) + page_offs, to_write, &data[written]);
      if (res != SPIFFS_OK) break;
      p_hdr.flags &= ~SPIFFS_PH_FLAG_FINAL;
      res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_UPDT,
          fd->file_nbr,
          SPIFFS_PAGE_TO_PADDR(fs, data_pix) + offsetof(spiffs_page_header, flags),
          sizeof(u8_t),
          (u8_t *)&p_hdr.flags);
      if (res != SPIFFS_OK) break;

      SPIFFS_DBG("modify: store to existing data page, src:%04x, dst:%04x:%04x offset:%i, len %i, written %i\n", orig_data_pix, data_pix, data_spix, page_offs, to_write, written);
    }

    // delete original data page
    res = spiffs_page_delete(fs, orig_data_pix);
    if (res != SPIFFS_OK) break;
    // update memory representation of object index page with new data page
    if (cur_objix_spix == 0) {
      // update object index header page
      ((spiffs_page_ix*)((u8_t *)objix_hdr + sizeof(spiffs_page_object_ix_header)))[data_spix] = data_pix;
      SPIFFS_DBG("modify: wrote page %04x to objix_hdr entry %02x in mem\n", data_pix, data_spix);
    } else {
      // update object index page
      ((spiffs_page_ix*)((u8_t *)objix + sizeof(spiffs_page_object_ix)))[SPIFFS_OBJ_IX_ENTRY(fs, data_spix)] = data_pix;
      SPIFFS_DBG("modify: wrote page %04x to objix entry %02x in mem\n", data_pix, SPIFFS_OBJ_IX_ENTRY(fs, data_spix));
    }

    // update internals
    page_offs = 0;
    data_spix++;
    written += to_write;
  } // while all data

  fd->offset = offset+written;
  fd->cursor_objix_pix = cur_objix_pix;
  fd->cursor_objix_spix = cur_objix_spix;

  // finalize updated object indices
  s32_t res2 = SPIFFS_OK;
  if (cur_objix_spix != 0) {
    // wrote beyond object index header page
    // write last modified object index page
    // move and update page
    spiffs_page_ix new_objix_pix;

    res2 = spiffs_page_index_check(fs, fd, cur_objix_pix, cur_objix_spix);
    SPIFFS_CHECK_RES(res2);

    res2 = spiffs_page_move(fs, fd->file_nbr, (u8_t*)objix, fd->obj_id, 0, cur_objix_pix, &new_objix_pix);
    SPIFFS_DBG("modify: store modified objix page, %04x:%04x, written %i\n", new_objix_pix, cur_objix_spix, written);
    fd->cursor_objix_pix = new_objix_pix;
    fd->cursor_objix_spix = cur_objix_spix;
    SPIFFS_CHECK_RES(res2);
    spiffs_cb_object_event(fs, fd, SPIFFS_EV_IX_UPD, fd->obj_id, objix->p_hdr.span_ix, new_objix_pix, 0);

  } else {
    // wrote within object index header page
    res2 = spiffs_object_update_index_hdr(fs, fd, fd->obj_id,
        fd->objix_hdr_pix, fs->work, 0, 0, &new_objix_hdr_pix);
    SPIFFS_DBG("modify: store modified objix_hdr page, %04x:%04x, written %i\n", new_objix_hdr_pix, 0, written);
    SPIFFS_CHECK_RES(res2);
  }

  return res;
} // spiffs_object_modify
#endif // !SPIFFS_READ_ONLY

static s32_t spiffs_object_find_object_index_header_by_name_v(
    spiffs *fs,
    spiffs_obj_id obj_id,
    spiffs_block_ix bix,
    int ix_entry,
    const void *user_const_p,
    void *user_var_p) {
  (void)user_var_p;
  s32_t res;
  spiffs_page_object_ix_header objix_hdr;
  spiffs_page_ix pix = SPIFFS_OBJ_LOOKUP_ENTRY_TO_PIX(fs, bix, ix_entry);
  if (obj_id == SPIFFS_OBJ_ID_FREE || obj_id == SPIFFS_OBJ_ID_DELETED ||
      (obj_id & SPIFFS_OBJ_ID_IX_FLAG) == 0) {
    return SPIFFS_VIS_COUNTINUE;
  }
  res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_LU2 | SPIFFS_OP_C_READ,
      0, SPIFFS_PAGE_TO_PADDR(fs, pix), sizeof(spiffs_page_object_ix_header), (u8_t *)&objix_hdr);
  SPIFFS_CHECK_RES(res);
  if (objix_hdr.p_hdr.span_ix == 0 &&
      (objix_hdr.p_hdr.flags & (SPIFFS_PH_FLAG_DELET | SPIFFS_PH_FLAG_FINAL | SPIFFS_PH_FLAG_IXDELE)) ==
          (SPIFFS_PH_FLAG_DELET | SPIFFS_PH_FLAG_IXDELE)) {
    if (strcmp((const char*)user_const_p, (char*)objix_hdr.name) == 0) {
      return SPIFFS_OK;
    }
  }

  return SPIFFS_VIS_COUNTINUE;
}

// Finds object index header page by name
s32_t spiffs_object_find_object_index_header_by_name(
    spiffs *fs,
    const u8_t name[SPIFFS_OBJ_NAME_LEN],
    spiffs_page_ix *pix) {
  s32_t res;
  spiffs_block_ix bix;
  int entry;

  res = spiffs_obj_lu_find_entry_visitor(fs,
      fs->cursor_block_ix,
      fs->cursor_obj_lu_entry,
      0,
      0,
      spiffs_object_find_object_index_header_by_name_v,
      name,
      0,
      &bix,
      &entry);

  if (res == SPIFFS_VIS_END) {
    res = SPIFFS_ERR_NOT_FOUND;
  }
  SPIFFS_CHECK_RES(res);

  if (pix) {
    *pix = SPIFFS_OBJ_LOOKUP_ENTRY_TO_PIX(fs, bix, entry);
  }

  fs->cursor_block_ix = bix;
  fs->cursor_obj_lu_entry = entry;

  return res;
}

#if !SPIFFS_READ_ONLY
// Truncates object to new size. If new size is null, object may be removed totally
s32_t spiffs_object_truncate(
    spiffs_fd *fd,
    u32_t new_size,
    u8_t remove) {
  s32_t res = SPIFFS_OK;
  spiffs *fs = fd->fs;

  if ((fd->size == SPIFFS_UNDEFINED_LEN || fd->size == 0) && !remove) {
    // no op
    return res;
  }

  // need 2 pages if not removing: object index page + possibly chopped data page
  if (remove == 0) {
    res = spiffs_gc_check(fs, SPIFFS_DATA_PAGE_SIZE(fs) * 2);
    SPIFFS_CHECK_RES(res);
  }

  spiffs_page_ix objix_pix = fd->objix_hdr_pix;
  spiffs_span_ix data_spix = (fd->size > 0 ? fd->size-1 : 0) / SPIFFS_DATA_PAGE_SIZE(fs);
  u32_t cur_size = fd->size == (u32_t)SPIFFS_UNDEFINED_LEN ? 0 : fd->size ;
  spiffs_span_ix cur_objix_spix = 0;
  spiffs_span_ix prev_objix_spix = (spiffs_span_ix)-1;
  spiffs_page_object_ix_header *objix_hdr = (spiffs_page_object_ix_header *)fs->work;
  spiffs_page_object_ix *objix = (spiffs_page_object_ix *)fs->work;
  spiffs_page_ix data_pix;
  spiffs_page_ix new_objix_hdr_pix;

  // before truncating, check if object is to be fully removed and mark this
  if (remove && new_size == 0) {
    u8_t flags = ~( SPIFFS_PH_FLAG_USED | SPIFFS_PH_FLAG_INDEX | SPIFFS_PH_FLAG_FINAL | SPIFFS_PH_FLAG_IXDELE);
    res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_IX | SPIFFS_OP_C_UPDT,
        fd->file_nbr, SPIFFS_PAGE_TO_PADDR(fs, fd->objix_hdr_pix) + offsetof(spiffs_page_header, flags),
        sizeof(u8_t),
        (u8_t *)&flags);
    SPIFFS_CHECK_RES(res);
  }

  // delete from end of object until desired len is reached
  while (cur_size > new_size) {
    cur_objix_spix = SPIFFS_OBJ_IX_ENTRY_SPAN_IX(fs, data_spix);

    // put object index for current data span index in work buffer
    if (prev_objix_spix != cur_objix_spix) {
      if (prev_objix_spix != (spiffs_span_ix)-1) {
        // remove previous object index page
        SPIFFS_DBG("truncate: delete objix page %04x:%04x\n", objix_pix, prev_objix_spix);

        res = spiffs_page_index_check(fs, fd, objix_pix, prev_objix_spix);
        SPIFFS_CHECK_RES(res);

        res = spiffs_page_delete(fs, objix_pix);
        SPIFFS_CHECK_RES(res);
        spiffs_cb_object_event(fs, fd, SPIFFS_EV_IX_DEL, fd->obj_id, objix->p_hdr.span_ix, objix_pix, 0);
        if (prev_objix_spix > 0) {
          // Update object index header page, unless we totally want to remove the file.
          // If fully removing, we're not keeping consistency as good as when storing the header between chunks,
          // would we be aborted. But when removing full files, a crammed system may otherwise
          // report ERR_FULL a la windows. We cannot have that.
          // Hence, take the risk - if aborted, a file check would free the lost pages and mend things
          // as the file is marked as fully deleted in the beginning.
          if (remove == 0) {
            SPIFFS_DBG("truncate: update objix hdr page %04x:%04x to size %i\n", fd->objix_hdr_pix, prev_objix_spix, cur_size);
            res = spiffs_object_update_index_hdr(fs, fd, fd->obj_id,
                fd->objix_hdr_pix, 0, 0, cur_size, &new_objix_hdr_pix);
            SPIFFS_CHECK_RES(res);
          }
          fd->size = cur_size;
        }
      }
      // load current object index (header) page
      if (cur_objix_spix == 0) {
        objix_pix = fd->objix_hdr_pix;
      } else {
        res = spiffs_obj_lu_find_id_and_span(fs, fd->obj_id | SPIFFS_OBJ_ID_IX_FLAG, cur_objix_spix, 0, &objix_pix);
        SPIFFS_CHECK_RES(res);
      }

      SPIFFS_DBG("truncate: load objix page %04x:%04x for data spix:%04x\n", objix_pix, cur_objix_spix, data_spix);
      res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_IX | SPIFFS_OP_C_READ,
          fd->file_nbr, SPIFFS_PAGE_TO_PADDR(fs, objix_pix), SPIFFS_CFG_LOG_PAGE_SZ(fs), fs->work);
      SPIFFS_CHECK_RES(res);
      SPIFFS_VALIDATE_OBJIX(objix_hdr->p_hdr, fd->obj_id, cur_objix_spix);
      fd->cursor_objix_pix = objix_pix;
      fd->cursor_objix_spix = cur_objix_spix;
      fd->offset = cur_size;

      prev_objix_spix = cur_objix_spix;
    }

    if (cur_objix_spix == 0) {
      // get data page from object index header page
      data_pix = ((spiffs_page_ix*)((u8_t *)objix_hdr + sizeof(spiffs_page_object_ix_header)))[data_spix];
      ((spiffs_page_ix*)((u8_t *)objix_hdr + sizeof(spiffs_page_object_ix_header)))[data_spix] = SPIFFS_OBJ_ID_FREE;
    } else {
      // get data page from object index page
      data_pix = ((spiffs_page_ix*)((u8_t *)objix + sizeof(spiffs_page_object_ix)))[SPIFFS_OBJ_IX_ENTRY(fs, data_spix)];
      ((spiffs_page_ix*)((u8_t *)objix + sizeof(spiffs_page_object_ix)))[SPIFFS_OBJ_IX_ENTRY(fs, data_spix)] = SPIFFS_OBJ_ID_FREE;
    }

    SPIFFS_DBG("truncate: got data pix %04x\n", data_pix);

    if (new_size == 0 || remove || cur_size - new_size >= SPIFFS_DATA_PAGE_SIZE(fs)) {
      // delete full data page
      res = spiffs_page_data_check(fs, fd, data_pix, data_spix);
      if (res != SPIFFS_ERR_DELETED && res != SPIFFS_OK && res != SPIFFS_ERR_INDEX_REF_FREE) {
        SPIFFS_DBG("truncate: err validating data pix %i\n", res);
        break;
      }

      if (res == SPIFFS_OK) {
        res = spiffs_page_delete(fs, data_pix);
        if (res != SPIFFS_OK) {
          SPIFFS_DBG("truncate: err deleting data pix %i\n", res);
          break;
        }
      } else if (res == SPIFFS_ERR_DELETED || res == SPIFFS_ERR_INDEX_REF_FREE) {
        res = SPIFFS_OK;
      }

      // update current size
      if (cur_size % SPIFFS_DATA_PAGE_SIZE(fs) == 0) {
        cur_size -= SPIFFS_DATA_PAGE_SIZE(fs);
      } else {
        cur_size -= cur_size % SPIFFS_DATA_PAGE_SIZE(fs);
      }
      fd->size = cur_size;
      fd->offset = cur_size;
      SPIFFS_DBG("truncate: delete data page %04x for data spix:%04x, cur_size:%i\n", data_pix, data_spix, cur_size);
    } else {
      // delete last page, partially
      spiffs_page_header p_hdr;
      spiffs_page_ix new_data_pix;
      u32_t bytes_to_remove = SPIFFS_DATA_PAGE_SIZE(fs) - (new_size % SPIFFS_DATA_PAGE_SIZE(fs));
      SPIFFS_DBG("truncate: delete %i bytes from data page %04x for data spix:%04x, cur_size:%i\n", bytes_to_remove, data_pix, data_spix, cur_size);

      res = spiffs_page_data_check(fs, fd, data_pix, data_spix);
      if (res != SPIFFS_OK) break;

      p_hdr.obj_id = fd->obj_id & ~SPIFFS_OBJ_ID_IX_FLAG;
      p_hdr.span_ix = data_spix;
      p_hdr.flags = 0xff;
      // allocate new page and copy unmodified data
      res = spiffs_page_allocate_data(fs, fd->obj_id & ~SPIFFS_OBJ_ID_IX_FLAG,
          &p_hdr, 0, 0, 0, 0, &new_data_pix);
      if (res != SPIFFS_OK) break;
      res = spiffs_phys_cpy(fs, 0,
          SPIFFS_PAGE_TO_PADDR(fs, new_data_pix) + sizeof(spiffs_page_header),
          SPIFFS_PAGE_TO_PADDR(fs, data_pix) + sizeof(spiffs_page_header),
          SPIFFS_DATA_PAGE_SIZE(fs) - bytes_to_remove);
      if (res != SPIFFS_OK) break;
      // delete original data page
      res = spiffs_page_delete(fs, data_pix);
      if (res != SPIFFS_OK) break;
      p_hdr.flags &= ~SPIFFS_PH_FLAG_FINAL;
      res = _spiffs_wr(fs, SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_UPDT,
          fd->file_nbr,
          SPIFFS_PAGE_TO_PADDR(fs, new_data_pix) + offsetof(spiffs_page_header, flags),
          sizeof(u8_t),
          (u8_t *)&p_hdr.flags);
      if (res != SPIFFS_OK) break;

      // update memory representation of object index page with new data page
      if (cur_objix_spix == 0) {
        // update object index header page
        ((spiffs_page_ix*)((u8_t *)objix_hdr + sizeof(spiffs_page_object_ix_header)))[data_spix] = new_data_pix;
        SPIFFS_DBG("truncate: wrote page %04x to objix_hdr entry %02x in mem\n", new_data_pix, SPIFFS_OBJ_IX_ENTRY(fs, data_spix));
      } else {
        // update object index page
        ((spiffs_page_ix*)((u8_t *)objix + sizeof(spiffs_page_object_ix)))[SPIFFS_OBJ_IX_ENTRY(fs, data_spix)] = new_data_pix;
        SPIFFS_DBG("truncate: wrote page %04x to objix entry %02x in mem\n", new_data_pix, SPIFFS_OBJ_IX_ENTRY(fs, data_spix));
      }
      cur_size = new_size;
      fd->size = new_size;
      fd->offset = cur_size;
      break;
    }
    data_spix--;
  } // while all data

  // update object indices
  if (cur_objix_spix == 0) {
    // update object index header page
    if (cur_size == 0) {
      if (remove) {
        // remove object altogether
        SPIFFS_DBG("truncate: remove object index header page %04x\n", objix_pix);

        res = spiffs_page_index_check(fs, fd, objix_pix, 0);
        SPIFFS_CHECK_RES(res);

        res = spiffs_page_delete(fs, objix_pix);
        SPIFFS_CHECK_RES(res);
        spiffs_cb_object_event(fs, fd, SPIFFS_EV_IX_DEL, fd->obj_id, 0, objix_pix, 0);
      } else {
        // make uninitialized object
        SPIFFS_DBG("truncate: reset objix_hdr page %04x\n", objix_pix);
        memset(fs->work + sizeof(spiffs_page_object_ix_header), 0xff,
            SPIFFS_CFG_LOG_PAGE_SZ(fs) - sizeof(spiffs_page_object_ix_header));
        res = spiffs_object_update_index_hdr(fs, fd, fd->obj_id,
            objix_pix, fs->work, 0, SPIFFS_UNDEFINED_LEN, &new_objix_hdr_pix);
        SPIFFS_CHECK_RES(res);
      }
    } else {
      // update object index header page
      SPIFFS_DBG("truncate: update object index header page with indices and size\n");
      res = spiffs_object_update_index_hdr(fs, fd, fd->obj_id,
          objix_pix, fs->work, 0, cur_size, &new_objix_hdr_pix);
      SPIFFS_CHECK_RES(res);
    }
  } else {
    // update both current object index page and object index header page
    spiffs_page_ix new_objix_pix;

    res = spiffs_page_index_check(fs, fd, objix_pix, cur_objix_spix);
    SPIFFS_CHECK_RES(res);

    // move and update object index page
    res = spiffs_page_move(fs, fd->file_nbr, (u8_t*)objix_hdr, fd->obj_id, 0, objix_pix, &new_objix_pix);
    SPIFFS_CHECK_RES(res);
    spiffs_cb_object_event(fs, fd, SPIFFS_EV_IX_UPD, fd->obj_id, objix->p_hdr.span_ix, new_objix_pix, 0);
    SPIFFS_DBG("truncate: store modified objix page, %04x:%04x\n", new_objix_pix, cur_objix_spix);
    fd->cursor_objix_pix = new_objix_pix;
    fd->cursor_objix_spix = cur_objix_spix;
    fd->offset = cur_size;
    // update object index header page with new size
    res = spiffs_object_update_index_hdr(fs, fd, fd->obj_id,
        fd->objix_hdr_pix, 0, 0, cur_size, &new_objix_hdr_pix);
    SPIFFS_CHECK_RES(res);
  }
  fd->size = cur_size;

  return res;
} // spiffs_object_truncate
#endif // !SPIFFS_READ_ONLY

s32_t spiffs_object_read(
    spiffs_fd *fd,
    u32_t offset,
    u32_t len,
    u8_t *dst) {
  s32_t res = SPIFFS_OK;
  spiffs *fs = fd->fs;
  spiffs_page_ix objix_pix;
  spiffs_page_ix data_pix;
  spiffs_span_ix data_spix = offset / SPIFFS_DATA_PAGE_SIZE(fs);
  u32_t cur_offset = offset;
  spiffs_span_ix cur_objix_spix;
  spiffs_span_ix prev_objix_spix = (spiffs_span_ix)-1;
  spiffs_page_object_ix_header *objix_hdr = (spiffs_page_object_ix_header *)fs->work;
  spiffs_page_object_ix *objix = (spiffs_page_object_ix *)fs->work;

  while (cur_offset < offset + len) {
    cur_objix_spix = SPIFFS_OBJ_IX_ENTRY_SPAN_IX(fs, data_spix);
    if (prev_objix_spix != cur_objix_spix) {
      // load current object index (header) page
      if (cur_objix_spix == 0) {
        objix_pix = fd->objix_hdr_pix;
      } else {
        SPIFFS_DBG("read: find objix %04x:%04x\n", fd->obj_id, cur_objix_spix);
        res = spiffs_obj_lu_find_id_and_span(fs, fd->obj_id | SPIFFS_OBJ_ID_IX_FLAG, cur_objix_spix, 0, &objix_pix);
        SPIFFS_CHECK_RES(res);
      }
      SPIFFS_DBG("read: load objix page %04x:%04x for data spix:%04x\n", objix_pix, cur_objix_spix, data_spix);
      res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_IX | SPIFFS_OP_C_READ,
          fd->file_nbr, SPIFFS_PAGE_TO_PADDR(fs, objix_pix), SPIFFS_CFG_LOG_PAGE_SZ(fs), fs->work);
      SPIFFS_CHECK_RES(res);
      SPIFFS_VALIDATE_OBJIX(objix->p_hdr, fd->obj_id, cur_objix_spix);

      fd->offset = cur_offset;
      fd->cursor_objix_pix = objix_pix;
      fd->cursor_objix_spix = cur_objix_spix;

      prev_objix_spix = cur_objix_spix;
    }

    if (cur_objix_spix == 0) {
      // get data page from object index header page
      data_pix = ((spiffs_page_ix*)((u8_t *)objix_hdr + sizeof(spiffs_page_object_ix_header)))[data_spix];
    } else {
      // get data page from object index page
      data_pix = ((spiffs_page_ix*)((u8_t *)objix + sizeof(spiffs_page_object_ix)))[SPIFFS_OBJ_IX_ENTRY(fs, data_spix)];
    }

    // all remaining data
    u32_t len_to_read = offset + len - cur_offset;
    // remaining data in page
    len_to_read = MIN(len_to_read, SPIFFS_DATA_PAGE_SIZE(fs) - (cur_offset % SPIFFS_DATA_PAGE_SIZE(fs)));
    // remaining data in file
    len_to_read = MIN(len_to_read, fd->size);
    SPIFFS_DBG("read: offset:%i rd:%i data spix:%04x is data_pix:%04x addr:%08x\n", cur_offset, len_to_read, data_spix, data_pix,
        SPIFFS_PAGE_TO_PADDR(fs, data_pix) + sizeof(spiffs_page_header) + (cur_offset % SPIFFS_DATA_PAGE_SIZE(fs)));
    if (len_to_read <= 0) {
      res = SPIFFS_ERR_END_OF_OBJECT;
      break;
    }
    res = spiffs_page_data_check(fs, fd, data_pix, data_spix);
    SPIFFS_CHECK_RES(res);
    res = _spiffs_rd(
        fs, SPIFFS_OP_T_OBJ_DA | SPIFFS_OP_C_READ,
        fd->file_nbr,
        SPIFFS_PAGE_TO_PADDR(fs, data_pix) + sizeof(spiffs_page_header) + (cur_offset % SPIFFS_DATA_PAGE_SIZE(fs)),
        len_to_read,
        dst);
    SPIFFS_CHECK_RES(res);
    dst += len_to_read;
    cur_offset += len_to_read;
    fd->offset = cur_offset;
    data_spix++;
  }

  return res;
}

#if !SPIFFS_READ_ONLY
typedef struct {
  spiffs_obj_id min_obj_id;
  spiffs_obj_id max_obj_id;
  u32_t compaction;
  const u8_t *conflicting_name;
} spiffs_free_obj_id_state;

static s32_t spiffs_obj_lu_find_free_obj_id_bitmap_v(spiffs *fs, spiffs_obj_id id, spiffs_block_ix bix, int ix_entry,
    const void *user_const_p, void *user_var_p) {
  if (id != SPIFFS_OBJ_ID_FREE && id != SPIFFS_OBJ_ID_DELETED) {
    spiffs_obj_id min_obj_id = *((spiffs_obj_id*)user_var_p);
    const u8_t *conflicting_name = (const u8_t*)user_const_p;

    // if conflicting name parameter is given, also check if this name is found in object index hdrs
    if (conflicting_name && (id & SPIFFS_OBJ_ID_IX_FLAG)) {
      spiffs_page_ix pix = SPIFFS_OBJ_LOOKUP_ENTRY_TO_PIX(fs, bix, ix_entry);
      int res;
      spiffs_page_object_ix_header objix_hdr;
      res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_LU2 | SPIFFS_OP_C_READ,
          0, SPIFFS_PAGE_TO_PADDR(fs, pix), sizeof(spiffs_page_object_ix_header), (u8_t *)&objix_hdr);
      SPIFFS_CHECK_RES(res);
      if (objix_hdr.p_hdr.span_ix == 0 &&
          (objix_hdr.p_hdr.flags & (SPIFFS_PH_FLAG_DELET | SPIFFS_PH_FLAG_FINAL | SPIFFS_PH_FLAG_IXDELE)) ==
              (SPIFFS_PH_FLAG_DELET | SPIFFS_PH_FLAG_IXDELE)) {
        if (strcmp((const char*)user_const_p, (char*)objix_hdr.name) == 0) {
          return SPIFFS_ERR_CONFLICTING_NAME;
        }
      }
    }

    id &= ~SPIFFS_OBJ_ID_IX_FLAG;
    u32_t bit_ix = (id-min_obj_id) & 7;
    int byte_ix = (id-min_obj_id) >> 3;
    if (byte_ix >= 0 && (u32_t)byte_ix < SPIFFS_CFG_LOG_PAGE_SZ(fs)) {
      fs->work[byte_ix] |= (1<<bit_ix);
    }
  }
  return SPIFFS_VIS_COUNTINUE;
}

static s32_t spiffs_obj_lu_find_free_obj_id_compact_v(spiffs *fs, spiffs_obj_id id, spiffs_block_ix bix, int ix_entry,
    const void *user_const_p, void *user_var_p) {
  (void)user_var_p;
  if (id != SPIFFS_OBJ_ID_FREE && id != SPIFFS_OBJ_ID_DELETED && (id & SPIFFS_OBJ_ID_IX_FLAG)) {
    s32_t res;
    const spiffs_free_obj_id_state *state = (const spiffs_free_obj_id_state*)user_const_p;
    spiffs_page_object_ix_header objix_hdr;

    res = _spiffs_rd(fs, SPIFFS_OP_T_OBJ_LU2 | SPIFFS_OP_C_READ,
        0, SPIFFS_OBJ_LOOKUP_ENTRY_TO_PADDR(fs, bix, ix_entry), sizeof(spiffs_page_object_ix_header), (u8_t*)&objix_hdr);
    if (res == SPIFFS_OK && objix_hdr.p_hdr.span_ix == 0 &&
        ((objix_hdr.p_hdr.flags & (SPIFFS_PH_FLAG_INDEX | SPIFFS_PH_FLAG_FINAL | SPIFFS_PH_FLAG_DELET)) ==
            (SPIFFS_PH_FLAG_DELET))) {
      // ok object look up entry
      if (state->conflicting_name && strcmp((const char *)state->conflicting_name, (char *)objix_hdr.name) == 0) {
        return SPIFFS_ERR_CONFLICTING_NAME;
      }

      id &= ~SPIFFS_OBJ_ID_IX_FLAG;
      if (id >= state->min_obj_id && id <= state->max_obj_id) {
        u8_t *map = (u8_t *)fs->work;
        int ix = (id - state->min_obj_id) / state->compaction;
        //SPIFFS_DBG("free_obj_id: add ix %i for id %04x min:%04x max%04x comp:%i\n", ix, id, state->min_obj_id, state->max_obj_id, state->compaction);
        map[ix]++;
      }
    }
  }
  return SPIFFS_VIS_COUNTINUE;
}

// Scans thru all object lookup for object index header pages. If total possible number of
// object ids cannot fit into a work buffer, these are grouped. When a group containing free
// object ids is found, the object lu is again scanned for object ids within group and bitmasked.
// Finally, the bitmask is searched for a free id
s32_t spiffs_obj_lu_find_free_obj_id(spiffs *fs, spiffs_obj_id *obj_id, const u8_t *conflicting_name) {
  s32_t res = SPIFFS_OK;
  u32_t max_objects = (fs->block_count * SPIFFS_OBJ_LOOKUP_MAX_ENTRIES(fs)) / 2;
  spiffs_free_obj_id_state state;
  spiffs_obj_id free_obj_id = SPIFFS_OBJ_ID_FREE;
  state.min_obj_id = 1;
  state.max_obj_id = max_objects + 1;
  if (state.max_obj_id & SPIFFS_OBJ_ID_IX_FLAG) {
    state.max_obj_id = ((spiffs_obj_id)-1) & ~SPIFFS_OBJ_ID_IX_FLAG;
  }
  state.compaction = 0;
  state.conflicting_name = conflicting_name;
  while (res == SPIFFS_OK && free_obj_id == SPIFFS_OBJ_ID_FREE) {
    if (state.max_obj_id - state.min_obj_id <= (spiffs_obj_id)SPIFFS_CFG_LOG_PAGE_SZ(fs)*8) {
      // possible to represent in bitmap
      u32_t i, j;
      SPIFFS_DBG("free_obj_id: BITM min:%04x max:%04x\n", state.min_obj_id, state.max_obj_id);

      memset(fs->work, 0, SPIFFS_CFG_LOG_PAGE_SZ(fs));
      res = spiffs_obj_lu_find_entry_visitor(fs, 0, 0, 0, 0, spiffs_obj_lu_find_free_obj_id_bitmap_v,
          conflicting_name, &state.min_obj_id, 0, 0);
      if (res == SPIFFS_VIS_END) res = SPIFFS_OK;
      SPIFFS_CHECK_RES(res);
      // traverse bitmask until found free obj_id
      for (i = 0; i < SPIFFS_CFG_LOG_PAGE_SZ(fs); i++) {
        u8_t mask = fs->work[i];
        if (mask == 0xff) {
          continue;
        }
        for (j = 0; j < 8; j++) {
          if ((mask & (1<<j)) == 0) {
            *obj_id = (i<<3)+j+state.min_obj_id;
            return SPIFFS_OK;
          }
        }
      }
      return SPIFFS_ERR_FULL;
    } else {
      // not possible to represent all ids in range in a bitmap, compact and count
      if (state.compaction != 0) {
        // select element in compacted table, decrease range and recompact
        u32_t i, min_i = 0;
        u8_t *map = (u8_t *)fs->work;
        u8_t min_count = 0xff;

        for (i = 0; i < SPIFFS_CFG_LOG_PAGE_SZ(fs)/sizeof(u8_t); i++) {
          if (map[i] < min_count) {
            min_count = map[i];
            min_i = i;
            if (min_count == 0) {
              break;
            }
          }
        }

        if (min_count == state.compaction) {
          // there are no free objids!
          SPIFFS_DBG("free_obj_id: compacted table is full\n");
          return SPIFFS_ERR_FULL;
        }

        SPIFFS_DBG("free_obj_id: COMP select index:%i min_count:%i min:%04x max:%04x compact:%i\n", min_i, min_count, state.min_obj_id, state.max_obj_id, state.compaction);

        if (min_count == 0) {
          // no id in this range, skip compacting and use directly
          *obj_id = min_i * state.compaction + state.min_obj_id;
          return SPIFFS_OK;
        } else {
          SPIFFS_DBG("free_obj_id: COMP SEL chunk:%04x min:%04x -> %04x\n", state.compaction, state.min_obj_id, state.min_obj_id + min_i *  state.compaction);
          state.min_obj_id += min_i *  state.compaction;
          state.max_obj_id = state.min_obj_id + state.compaction;
          // decrease compaction
        }
        if ((state.max_obj_id - state.min_obj_id <= (spiffs_obj_id)SPIFFS_CFG_LOG_PAGE_SZ(fs)*8)) {
          // no need for compacting, use bitmap
          continue;
        }
      }
      // in a work memory of log_page_size bytes, we may fit in log_page_size ids
      // todo what if compaction is > 255 - then we cannot fit it in a byte
      state.compaction = (state.max_obj_id-state.min_obj_id) / ((SPIFFS_CFG_LOG_PAGE_SZ(fs) / sizeof(u8_t)));
      SPIFFS_DBG("free_obj_id: COMP min:%04x max:%04x compact:%i\n", state.min_obj_id, state.max_obj_id, state.compaction);

      memset(fs->work, 0, SPIFFS_CFG_LOG_PAGE_SZ(fs));
      res = spiffs_obj_lu_find_entry_visitor(fs, 0, 0, 0, 0, spiffs_obj_lu_find_free_obj_id_compact_v, &state, 0, 0, 0);
      if (res == SPIFFS_VIS_END) res = SPIFFS_OK;
      SPIFFS_CHECK_RES(res);
      state.conflicting_name = 0; // searched for conflicting name once, no need to do it again
    }
  }

  return res;
}
#endif // !SPIFFS_READ_ONLY

s32_t spiffs_fd_find_new(spiffs *fs, spiffs_fd **fd) {
  u32_t i;
  spiffs_fd *fds = (spiffs_fd *)fs->fd_space;
  for (i = 0; i < fs->fd_count; i++) {
    spiffs_fd *cur_fd = &fds[i];
    if (cur_fd->file_nbr == 0) {
      cur_fd->file_nbr = i+1;
      *fd = cur_fd;
      return SPIFFS_OK;
    }
  }
  return SPIFFS_ERR_OUT_OF_FILE_DESCS;
}

s32_t spiffs_fd_return(spiffs *fs, spiffs_file f) {
  if (f <= 0 || f > (s16_t)fs->fd_count) {
    return SPIFFS_ERR_BAD_DESCRIPTOR;
  }
  spiffs_fd *fds = (spiffs_fd *)fs->fd_space;
  spiffs_fd *fd = &fds[f-1];
  if (fd->file_nbr == 0) {
    return SPIFFS_ERR_FILE_CLOSED;
  }
  fd->file_nbr = 0;
  return SPIFFS_OK;
}

s32_t spiffs_fd_get(spiffs *fs, spiffs_file f, spiffs_fd **fd) {
  if (f <= 0 || f > (s16_t)fs->fd_count) {
    return SPIFFS_ERR_BAD_DESCRIPTOR;
  }
  spiffs_fd *fds = (spiffs_fd *)fs->fd_space;
  *fd = &fds[f-1];
  if ((*fd)->file_nbr == 0) {
    return SPIFFS_ERR_FILE_CLOSED;
  }
  return SPIFFS_OK;
}