text: #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 "_SPIPRIad":"_SPIPRIi"\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 we have sane number of blocks
    if (bix_count[0] < 3) return SPIFFS_ERR_PROBE_TOO_FEW_BLOCKS;
    // check that the order is correct, take aborted erases in calculation
    // first block aborted erase
    if (magic[0] == (spiffs_obj_id)(-1) && bix_count[1] - bix_count[2] == 1) {
      return (bix_count[1]+1) * cfg->log_block_size;
    }
    // second block aborted erase
    if (magic[1] == (spiffs_obj_id)(-1) && bix_count[0] - bix_count[2] == 2) {
      return bix_count[0] * cfg->log_block_size;
    }
    // third block aborted erase
    if (magic[2] == (spiffs_obj_id)(-1) && bix_count[0] - bix_count[1] == 1) {
      return bix_count[0] * cfg->log_block_size;
    }
    // no block has aborted erase
    if (bix_count[0] - bix_count[1] == 1 && bix_count[1] - bix_count[2] == 1) {
      return bix_count[0] * cfg->log_block_size;
    }
  
    return SPIFFS_ERR_PROBE_NOT_A_FS;
  }
  #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 "_SPIPRIbl"\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) + 1;
      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_IX_MAP
  
  // update index map of given fd with given object index data
  static void spiffs_update_ix_map(spiffs *fs,
      spiffs_fd *fd, spiffs_span_ix objix_spix, spiffs_page_object_ix *objix) {
  #if SPIFFS_SINGLETON
    (void)fs;
  #endif
    spiffs_ix_map *map = fd->ix_map;
    spiffs_span_ix map_objix_start_spix = SPIFFS_OBJ_IX_ENTRY_SPAN_IX(fs, map->start_spix);
    spiffs_span_ix map_objix_end_spix = SPIFFS_OBJ_IX_ENTRY_SPAN_IX(fs, map->end_spix);
  
    // check if updated ix is within map range
    if (objix_spix < map_objix_start_spix || objix_spix > map_objix_end_spix) {
      return;
    }
  
    // update memory mapped page index buffer to new pages
  
    // get range of updated object index map data span indices
    spiffs_span_ix objix_data_spix_start =
        SPIFFS_DATA_SPAN_IX_FOR_OBJ_IX_SPAN_IX(fs, objix_spix);
    spiffs_span_ix objix_data_spix_end = objix_data_spix_start +
        (objix_spix == 0 ? SPIFFS_OBJ_HDR_IX_LEN(fs) : SPIFFS_OBJ_IX_LEN(fs));
  
    // calc union of object index range and index map range array
    spiffs_span_ix map_spix = MAX(map->start_spix, objix_data_spix_start);
    spiffs_span_ix map_spix_end = MIN(map->end_spix + 1, objix_data_spix_end);
  
    while (map_spix < map_spix_end) {
      spiffs_page_ix objix_data_pix;
      if (objix_spix == 0) {
        // get data page from object index header page
        objix_data_pix = ((spiffs_page_ix*)((u8_t *)objix + sizeof(spiffs_page_object_ix_header)))[map_spix];
      } else {
        // get data page from object index page
        objix_data_pix = ((spiffs_page_ix*)((u8_t *)objix + sizeof(spiffs_page_object_ix)))[SPIFFS_OBJ_IX_ENTRY(fs, map_spix)];
      }
  
      if (objix_data_pix == (spiffs_page_ix)-1) {
        // reached end of object, abort
        break;
      }
  
      map->map_buf[map_spix - map->start_spix] = objix_data_pix;
      SPIFFS_DBG("map "_SPIPRIid":"_SPIPRIsp" ("_SPIPRIsp"--"_SPIPRIsp") objix.spix:"_SPIPRIsp" to pix "_SPIPRIpg"\n",
          fd->obj_id, map_spix - map->start_spix,
          map->start_spix, map->end_spix,
          objix->p_hdr.span_ix,
          objix_data_pix);
  
      map_spix++;
    }
  }
  
  typedef struct {
    spiffs_fd *fd;
    u32_t remaining_objix_pages_to_visit;
    spiffs_span_ix map_objix_start_spix;
    spiffs_span_ix map_objix_end_spix;
  } spiffs_ix_map_populate_state;
  
  static s32_t spiffs_populate_ix_map_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_const_p;
    s32_t res;
    spiffs_ix_map_populate_state *state = (spiffs_ix_map_populate_state *)user_var_p;
    spiffs_page_ix pix = SPIFFS_OBJ_LOOKUP_ENTRY_TO_PIX(fs, bix, ix_entry);
  
    // load header to check it
    spiffs_page_object_ix *objix = (spiffs_page_object_ix *)fs->work;
    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), (u8_t *)objix);
    SPIFFS_CHECK_RES(res);
    SPIFFS_VALIDATE_OBJIX(objix->p_hdr, obj_id, objix->p_hdr.span_ix);
  
    // check if hdr is ok, and if objix range overlap with ix map range
    if ((objix->p_hdr.flags & (SPIFFS_PH_FLAG_DELET | SPIFFS_PH_FLAG_FINAL | SPIFFS_PH_FLAG_IXDELE)) ==
        (SPIFFS_PH_FLAG_DELET | SPIFFS_PH_FLAG_IXDELE) &&
        objix->p_hdr.span_ix >= state->map_objix_start_spix &&
        objix->p_hdr.span_ix <= state->map_objix_end_spix) {
      // ok, load rest of object index
      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),
          SPIFFS_CFG_LOG_PAGE_SZ(fs) - sizeof(spiffs_page_object_ix),
          (u8_t *)objix + sizeof(spiffs_page_object_ix));
      SPIFFS_CHECK_RES(res);
  
      spiffs_update_ix_map(fs, state->fd, objix->p_hdr.span_ix, objix);
  
      state->remaining_objix_pages_to_visit--;
      SPIFFS_DBG("map "_SPIPRIid" ("_SPIPRIsp"--"_SPIPRIsp") remaining objix pages "_SPIPRIi"\n",
          state->fd->obj_id,
          state->fd->ix_map->start_spix, state->fd->ix_map->end_spix,
          state->remaining_objix_pages_to_visit);
    }
  
    if (res == SPIFFS_OK) {
      res = state->remaining_objix_pages_to_visit ? SPIFFS_VIS_COUNTINUE : SPIFFS_VIS_END;
    }
    return res;
  }
  
  // populates index map, from vector entry start to vector entry end, inclusive
  s32_t spiffs_populate_ix_map(spiffs *fs, spiffs_fd *fd, u32_t vec_entry_start, u32_t vec_entry_end) {
    s32_t res;
    spiffs_ix_map *map = fd->ix_map;
    spiffs_ix_map_populate_state state;
    vec_entry_start = MIN((map->end_spix - map->start_spix + 1) - 1, (s32_t)vec_entry_start);
    vec_entry_end = MAX((map->end_spix - map->start_spix + 1) - 1, (s32_t)vec_entry_end);
    if (vec_entry_start > vec_entry_end) {
      return SPIFFS_ERR_IX_MAP_BAD_RANGE;
    }
    state.map_objix_start_spix = SPIFFS_OBJ_IX_ENTRY_SPAN_IX(fs, map->start_spix + vec_entry_start);
    state.map_objix_end_spix = SPIFFS_OBJ_IX_ENTRY_SPAN_IX(fs, map->start_spix + vec_entry_end);
    state.remaining_objix_pages_to_visit =
        state.map_objix_end_spix - state.map_objix_start_spix + 1;
    state.fd = fd;
  
    res = spiffs_obj_lu_find_entry_visitor(
        fs,
        SPIFFS_BLOCK_FOR_PAGE(fs, fd->objix_hdr_pix),
        SPIFFS_OBJ_LOOKUP_ENTRY_FOR_PAGE(fs, fd->objix_hdr_pix),
        SPIFFS_VIS_CHECK_ID,
        fd->obj_id | SPIFFS_OBJ_ID_IX_FLAG,
        spiffs_populate_ix_map_v,
        0,
        &state,
        0,
        0);
  
    if (res == SPIFFS_VIS_END) {
      res = SPIFFS_OK;
    }
  
    return res;
  }
  
  #endif
  
  
  #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[],
      const u8_t meta[],
      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 @ "_SPIPRIpg" bix:"_SPIPRIbl" entry:"_SPIPRIsp"\n", (spiffs_page_ix)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);
  #if SPIFFS_OBJ_META_LEN
    if (meta) {
      memcpy(oix_hdr.meta, meta, SPIFFS_OBJ_META_LEN);
    } else {
      memset(oix_hdr.meta, 0xff, SPIFFS_OBJ_META_LEN);
    }
  #else
    (void) meta;
  #endif
  
    // 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, (spiffs_page_object_ix *)&oix_hdr,
        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[],
      const u8_t meta[],
      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 SPIFFS_OBJ_META_LEN
    if (meta) {
      memcpy(objix_hdr->meta, meta, SPIFFS_OBJ_META_LEN);
    }
  #else
    (void) meta;
  #endif
    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, (spiffs_page_object_ix *)objix_hdr,
          new_objix_hdr_data ? SPIFFS_EV_IX_UPD : SPIFFS_EV_IX_UPD_HDR,
              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_page_object_ix *objix,
      int ev,
      spiffs_obj_id obj_id_raw,
      spiffs_span_ix spix,
      spiffs_page_ix new_pix,
      u32_t new_size) {
  #if SPIFFS_IX_MAP == 0
    (void)objix;
  #endif
    // 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 SPIFFS_TEMPORAL_FD_CACHE
      if (cur_fd->score == 0 || (cur_fd->obj_id & ~SPIFFS_OBJ_ID_IX_FLAG) != obj_id) continue;
  #else
      if (cur_fd->file_nbr == 0 || (cur_fd->obj_id & ~SPIFFS_OBJ_ID_IX_FLAG) != obj_id) continue;
  #endif
      if (spix == 0) {
        if (ev != SPIFFS_EV_IX_DEL) {
          SPIFFS_DBG("       callback: setting fd "_SPIPRIfd":"_SPIPRIid" objix_hdr_pix to "_SPIPRIpg", size:"_SPIPRIi"\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 {
          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_DEL) {
          SPIFFS_DBG("       callback: setting fd "_SPIPRIfd":"_SPIPRIid" span:"_SPIPRIsp" objix_pix to "_SPIPRIpg"\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;
        }
      }
    }
  
  #if SPIFFS_IX_MAP
  
    // update index maps
    if (ev == SPIFFS_EV_IX_UPD || ev == SPIFFS_EV_IX_NEW) {
      for (i = 0; i < fs->fd_count; i++) {
        spiffs_fd *cur_fd = &fds[i];
        // check fd opened, having ix map, match obj id
        if (cur_fd->file_nbr == 0 ||
            cur_fd->ix_map == 0 ||
            (cur_fd->obj_id & ~SPIFFS_OBJ_ID_IX_FLAG) != obj_id) continue;
        SPIFFS_DBG("       callback: map ix update fd "_SPIPRIfd":"_SPIPRIid" span:"_SPIPRIsp"\n", cur_fd->file_nbr, cur_fd->obj_id, spix);
        spiffs_update_ix_map(fs, cur_fd, spix, objix);
      }
    }
  
  #endif
  
    // 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 ||
          ev == SPIFFS_EV_IX_MOV ||
          ev == SPIFFS_EV_IX_UPD_HDR) {
        op = SPIFFS_CB_UPDATED;
      } else if (ev == SPIFFS_EV_IX_DEL) {
        op = SPIFFS_CB_DELETED;
      } else {
        SPIFFS_DBG("       callback: WARNING unknown callback event "_SPIPRIi"\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 "_SPIPRIfd" is obj id "_SPIPRIid"\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: "_SPIPRIi" bytes @ offs "_SPIPRIi" of size "_SPIPRIi"\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 "_SPIPRIi"\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: "_SPIPRIid" store objix "_SPIPRIpg":"_SPIPRIsp", written "_SPIPRIi"\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, 0, offset+written, &new_objix_hdr_page);
              SPIFFS_CHECK_RES(res);
              SPIFFS_DBG("append: "_SPIPRIid" store new objix_hdr, "_SPIPRIpg":"_SPIPRIsp", written "_SPIPRIi"\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, (spiffs_page_object_ix *)fs->work,
                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, 0, offset+written, &new_objix_hdr_page);
            SPIFFS_CHECK_RES(res);
            SPIFFS_DBG("append: "_SPIPRIid" store new size I "_SPIPRIi" in objix_hdr, "_SPIPRIpg":"_SPIPRIsp", written "_SPIPRIi"\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: "_SPIPRIid" load objixhdr page "_SPIPRIpg":"_SPIPRIsp"\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);
            // 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_cb_object_event(fs, (spiffs_page_object_ix *)fs->work,
                SPIFFS_EV_IX_NEW, fd->obj_id, cur_objix_spix, cur_objix_pix, 0);
            SPIFFS_DBG("append: "_SPIPRIid" create objix page, "_SPIPRIpg":"_SPIPRIsp", written "_SPIPRIi"\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: "_SPIPRIid" find objix span_ix:"_SPIPRIsp"\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: "_SPIPRIid" found object index at page "_SPIPRIpg" [fd size "_SPIPRIi"]\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: "_SPIPRIid" store new data page, "_SPIPRIpg":"_SPIPRIsp" offset:"_SPIPRIi", len "_SPIPRIi", written "_SPIPRIi"\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: "_SPIPRIid" store to existing data page, "_SPIPRIpg":"_SPIPRIsp" offset:"_SPIPRIi", len "_SPIPRIi", written "_SPIPRIi"\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: "_SPIPRIid" wrote page "_SPIPRIpg" to objix_hdr entry "_SPIPRIsp" 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: "_SPIPRIid" wrote page "_SPIPRIpg" to objix entry "_SPIPRIsp" in mem\n", fd->obj_id
            , data_page, (spiffs_span_ix)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: "_SPIPRIid" store objix page, "_SPIPRIpg":"_SPIPRIsp", written "_SPIPRIi"\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, (spiffs_page_object_ix *)fs->work,
          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, 0, offset+written, &new_objix_hdr_page);
      SPIFFS_DBG("append: "_SPIPRIid" store new size II "_SPIPRIi" in objix_hdr, "_SPIPRIpg":"_SPIPRIsp", written "_SPIPRIi", res "_SPIPRIi"\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: "_SPIPRIid" store fresh objix_hdr page, "_SPIPRIpg":"_SPIPRIsp", written "_SPIPRIi"\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, (spiffs_page_object_ix *)fs->work,
            SPIFFS_EV_IX_UPD_HDR, 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, 0, offset+written, &new_objix_hdr_page);
        SPIFFS_DBG("append: "_SPIPRIid" store modified objix_hdr page, "_SPIPRIpg":"_SPIPRIsp", written "_SPIPRIi"\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, 0, &new_objix_hdr_pix);
            SPIFFS_DBG("modify: store modified objix_hdr page, "_SPIPRIpg":"_SPIPRIsp", written "_SPIPRIi"\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, "_SPIPRIid":"_SPIPRIsp", written "_SPIPRIi"\n", new_objix_pix, objix->p_hdr.span_ix, written);
            SPIFFS_CHECK_RES(res);
            spiffs_cb_object_event(fs, (spiffs_page_object_ix *)objix,
                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 "_SPIPRIpg":"_SPIPRIsp"\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:"_SPIPRIsp"\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 "_SPIPRIpg"\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, "_SPIPRIpg":"_SPIPRIsp" offset:"_SPIPRIi", len "_SPIPRIi", written "_SPIPRIi"\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:"_SPIPRIpg", dst:"_SPIPRIpg":"_SPIPRIsp" offset:"_SPIPRIi", len "_SPIPRIi", written "_SPIPRIi"\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 "_SPIPRIpg" to objix_hdr entry "_SPIPRIsp" 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 "_SPIPRIpg" to objix entry "_SPIPRIsp" in mem\n", data_pix, (spiffs_span_ix)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, "_SPIPRIpg":"_SPIPRIsp", written "_SPIPRIi"\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, (spiffs_page_object_ix *)objix,
          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, 0, &new_objix_hdr_pix);
      SPIFFS_DBG("modify: store modified objix_hdr page, "_SPIPRIpg":"_SPIPRIsp", written "_SPIPRIi"\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_full) {
    s32_t res = SPIFFS_OK;
    spiffs *fs = fd->fs;
  
    if ((fd->size == SPIFFS_UNDEFINED_LEN || fd->size == 0) && !remove_full) {
      // no op
      return res;
    }
  
    // need 2 pages if not removing: object index page + possibly chopped data page
    if (remove_full == 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_full && 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 "_SPIPRIpg":"_SPIPRIsp"\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, (spiffs_page_object_ix *)0,
              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_full == 0) {
              SPIFFS_DBG("truncate: update objix hdr page "_SPIPRIpg":"_SPIPRIsp" to size "_SPIPRIi"\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, 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 "_SPIPRIpg":"_SPIPRIsp" for data spix:"_SPIPRIsp"\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 "_SPIPRIpg"\n", data_pix);
  
      if (new_size == 0 || remove_full || 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 "_SPIPRIi"\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 "_SPIPRIi"\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 "_SPIPRIpg" for data spix:"_SPIPRIsp", cur_size:"_SPIPRIi"\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 "_SPIPRIi" bytes from data page "_SPIPRIpg" for data spix:"_SPIPRIsp", cur_size:"_SPIPRIi"\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 "_SPIPRIpg" to objix_hdr entry "_SPIPRIsp" in mem\n", new_data_pix, (spiffs_span_ix)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 "_SPIPRIpg" to objix entry "_SPIPRIsp" in mem\n", new_data_pix, (spiffs_span_ix)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_full) {
          // remove object altogether
          SPIFFS_DBG("truncate: remove object index header page "_SPIPRIpg"\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, (spiffs_page_object_ix *)0,
              SPIFFS_EV_IX_DEL, fd->obj_id, 0, objix_pix, 0);
        } else {
          // make uninitialized object
          SPIFFS_DBG("truncate: reset objix_hdr page "_SPIPRIpg"\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, 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, 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, (spiffs_page_object_ix *)objix_hdr,
          SPIFFS_EV_IX_UPD, fd->obj_id, objix->p_hdr.span_ix, new_objix_pix, 0);
      SPIFFS_DBG("truncate: store modified objix page, "_SPIPRIpg":"_SPIPRIsp"\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, 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) {
  #if SPIFFS_IX_MAP
      // check if we have a memory, index map and if so, if we're within index map's range
      // and if so, if the entry is populated
      if (fd->ix_map && data_spix >= fd->ix_map->start_spix && data_spix <= fd->ix_map->end_spix
          && fd->ix_map->map_buf[data_spix - fd->ix_map->start_spix]) {
        data_pix = fd->ix_map->map_buf[data_spix - fd->ix_map->start_spix];
      } else {
  #endif
        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 "_SPIPRIid":"_SPIPRIsp"\n", fd->obj_id, cur_objix_spix);
            if (fd->cursor_objix_spix == cur_objix_spix) {
              objix_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, &objix_pix);
              SPIFFS_CHECK_RES(res);
            }
          }
          SPIFFS_DBG("read: load objix page "_SPIPRIpg":"_SPIPRIsp" for data spix:"_SPIPRIsp"\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)];
        }
  #if SPIFFS_IX_MAP
      }
  #endif
      // 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:"_SPIPRIi" rd:"_SPIPRIi" data spix:"_SPIPRIsp" is data_pix:"_SPIPRIpg" addr:"_SPIPRIad"\n", cur_offset, len_to_read, data_spix, data_pix,
          (u32_t)(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 "_SPIPRIi" for id "_SPIPRIid" min"_SPIPRIid" max"_SPIPRIid" comp:"_SPIPRIi"\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:"_SPIPRIid" max:"_SPIPRIid"\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:"_SPIPRIi" min_count:"_SPIPRIi" min:"_SPIPRIid" max:"_SPIPRIid" compact:"_SPIPRIi"\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:"_SPIPRIi" min:"_SPIPRIid" -> "_SPIPRIid"\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:"_SPIPRIid" max:"_SPIPRIid" compact:"_SPIPRIi"\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
  
  #if SPIFFS_TEMPORAL_FD_CACHE
  // djb2 hash
  static u32_t spiffs_hash(spiffs *fs, const u8_t *name) {
    (void)fs;
    u32_t hash = 5381;
    u8_t c;
    int i = 0;
    while ((c = name[i++]) && i < SPIFFS_OBJ_NAME_LEN) {
      hash = (hash * 33) ^ c;
    }
    return hash;
  }
  #endif
  
  s32_t spiffs_fd_find_new(spiffs *fs, spiffs_fd **fd, const char *name) {
  #if SPIFFS_TEMPORAL_FD_CACHE
    u32_t i;
    u16_t min_score = 0xffff;
    u32_t cand_ix = (u32_t)-1;
    u32_t name_hash = name ? spiffs_hash(fs, (const u8_t *)name) : 0;
    spiffs_fd *fds = (spiffs_fd *)fs->fd_space;
  
    if (name) {
      // first, decrease score of all closed descriptors
      for (i = 0; i < fs->fd_count; i++) {
        spiffs_fd *cur_fd = &fds[i];
        if (cur_fd->file_nbr == 0) {
          if (cur_fd->score > 1) { // score == 0 indicates never used fd
            cur_fd->score--;
          }
        }
      }
    }
  
    // find the free fd with least score
    for (i = 0; i < fs->fd_count; i++) {
      spiffs_fd *cur_fd = &fds[i];
      if (cur_fd->file_nbr == 0) {
        if (name && cur_fd->name_hash == name_hash) {
          cand_ix = i;
          break;
        }
        if (cur_fd->score < min_score) {
          min_score = cur_fd->score;
          cand_ix = i;
        }
      }
    }
  
    if (cand_ix != (u32_t)-1) {
      spiffs_fd *cur_fd = &fds[cand_ix];
      if (name) {
        if (cur_fd->name_hash == name_hash && cur_fd->score > 0) {
          // opened an fd with same name hash, assume same file
          // set search point to saved obj index page and hope we have a correct match directly
          // when start searching - if not, we will just keep searching until it is found
          fs->cursor_block_ix = SPIFFS_BLOCK_FOR_PAGE(fs, cur_fd->objix_hdr_pix);
          fs->cursor_obj_lu_entry = SPIFFS_OBJ_LOOKUP_ENTRY_FOR_PAGE(fs, cur_fd->objix_hdr_pix);
          // update score
          if (cur_fd->score < 0xffff-SPIFFS_TEMPORAL_CACHE_HIT_SCORE) {
            cur_fd->score += SPIFFS_TEMPORAL_CACHE_HIT_SCORE;
          } else {
            cur_fd->score = 0xffff;
          }
        } else {
          // no hash hit, restore this fd to initial state
          cur_fd->score = SPIFFS_TEMPORAL_CACHE_HIT_SCORE;
          cur_fd->name_hash = name_hash;
        }
      }
      cur_fd->file_nbr = cand_ix+1;
      *fd = cur_fd;
      return SPIFFS_OK;
    } else {
      return SPIFFS_ERR_OUT_OF_FILE_DESCS;
    }
  #else
    (void)name;
    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;
  #endif
  }
  
  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;
  #if SPIFFS_IX_MAP
    fd->ix_map = 0;
  #endif
    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;
  }
  
  #if SPIFFS_TEMPORAL_FD_CACHE
  void spiffs_fd_temporal_cache_rehash(
      spiffs *fs,
      const char *old_path,
      const char *new_path) {
    u32_t i;
    u32_t old_hash = spiffs_hash(fs, (const u8_t *)old_path);
    u32_t new_hash = spiffs_hash(fs, (const u8_t *)new_path);
    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->score > 0 && cur_fd->name_hash == old_hash) {
        cur_fd->name_hash = new_hash;
      }
    }
  }
  #endif
  