text: /*
   * The little filesystem
   *
   * Copyright (c) 2017 ARM Limited
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  #include "lfs.h"
  #include "lfs_util.h"
  
  #include <string.h>
  #include <stdlib.h>
  #include <assert.h>
  
  
  /// Caching block device operations ///
  static int lfs_cache_read(lfs_t *lfs, lfs_cache_t *rcache,
          const lfs_cache_t *pcache, lfs_block_t block,
          lfs_off_t off, void *buffer, lfs_size_t size) {
      uint8_t *data = buffer;
      assert(block < lfs->cfg->block_count);
  
      while (size > 0) {
          if (pcache && block == pcache->block && off >= pcache->off &&
                  off < pcache->off + lfs->cfg->prog_size) {
              // is already in pcache?
              lfs_size_t diff = lfs_min(size,
                      lfs->cfg->prog_size - (off-pcache->off));
              memcpy(data, &pcache->buffer[off-pcache->off], diff);
  
              data += diff;
              off += diff;
              size -= diff;
              continue;
          }
  
          if (block == rcache->block && off >= rcache->off &&
                  off < rcache->off + lfs->cfg->read_size) {
              // is already in rcache?
              lfs_size_t diff = lfs_min(size,
                      lfs->cfg->read_size - (off-rcache->off));
              memcpy(data, &rcache->buffer[off-rcache->off], diff);
  
              data += diff;
              off += diff;
              size -= diff;
              continue;
          }
  
          if (off % lfs->cfg->read_size == 0 && size >= lfs->cfg->read_size) {
              // bypass cache?
              lfs_size_t diff = size - (size % lfs->cfg->read_size);
              int err = lfs->cfg->read(lfs->cfg, block, off, data, diff);
              if (err) {
                  return err;
              }
  
              data += diff;
              off += diff;
              size -= diff;
              continue;
          }
  
          // load to cache, first condition can no longer fail
          rcache->block = block;
          rcache->off = off - (off % lfs->cfg->read_size);
          int err = lfs->cfg->read(lfs->cfg, rcache->block,
                  rcache->off, rcache->buffer, lfs->cfg->read_size);
          if (err) {
              return err;
          }
      }
  
      return 0;
  }
  
  static int lfs_cache_cmp(lfs_t *lfs, lfs_cache_t *rcache,
          const lfs_cache_t *pcache, lfs_block_t block,
          lfs_off_t off, const void *buffer, lfs_size_t size) {
      const uint8_t *data = buffer;
  
      for (lfs_off_t i = 0; i < size; i++) {
          uint8_t c;
          int err = lfs_cache_read(lfs, rcache, pcache,
                  block, off+i, &c, 1);
          if (err) {
              return err;
          }
  
          if (c != data[i]) {
              return false;
          }
      }
  
      return true;
  }
  
  static int lfs_cache_crc(lfs_t *lfs, lfs_cache_t *rcache,
          const lfs_cache_t *pcache, lfs_block_t block,
          lfs_off_t off, lfs_size_t size, uint32_t *crc) {
      for (lfs_off_t i = 0; i < size; i++) {
          uint8_t c;
          int err = lfs_cache_read(lfs, rcache, pcache,
                  block, off+i, &c, 1);
          if (err) {
              return err;
          }
  
          lfs_crc(crc, &c, 1);
      }
  
      return 0;
  }
  
  static int lfs_cache_flush(lfs_t *lfs,
          lfs_cache_t *pcache, lfs_cache_t *rcache) {
      if (pcache->block != 0xffffffff) {
          int err = lfs->cfg->prog(lfs->cfg, pcache->block,
                  pcache->off, pcache->buffer, lfs->cfg->prog_size);
          if (err) {
              return err;
          }
  
          if (rcache) {
              int res = lfs_cache_cmp(lfs, rcache, NULL, pcache->block,
                      pcache->off, pcache->buffer, lfs->cfg->prog_size);
              if (res < 0) {
                  return res;
              }
  
              if (!res) {
                  return LFS_ERR_CORRUPT;
              }
          }
  
          pcache->block = 0xffffffff;
      }
  
      return 0;
  }
  
  static int lfs_cache_prog(lfs_t *lfs, lfs_cache_t *pcache,
          lfs_cache_t *rcache, lfs_block_t block,
          lfs_off_t off, const void *buffer, lfs_size_t size) {
      const uint8_t *data = buffer;
      assert(block < lfs->cfg->block_count);
  
      while (size > 0) {
          if (block == pcache->block && off >= pcache->off &&
                  off < pcache->off + lfs->cfg->prog_size) {
              // is already in pcache?
              lfs_size_t diff = lfs_min(size,
                      lfs->cfg->prog_size - (off-pcache->off));
              memcpy(&pcache->buffer[off-pcache->off], data, diff);
  
              data += diff;
              off += diff;
              size -= diff;
  
              if (off % lfs->cfg->prog_size == 0) {
                  // eagerly flush out pcache if we fill up
                  int err = lfs_cache_flush(lfs, pcache, rcache);
                  if (err) {
                      return err;
                  }
              }
  
              continue;
          }
  
          // pcache must have been flushed, either by programming and
          // entire block or manually flushing the pcache
          assert(pcache->block == 0xffffffff);
  
          if (off % lfs->cfg->prog_size == 0 &&
                  size >= lfs->cfg->prog_size) {
              // bypass pcache?
              lfs_size_t diff = size - (size % lfs->cfg->prog_size);
              int err = lfs->cfg->prog(lfs->cfg, block, off, data, diff);
              if (err) {
                  return err;
              }
  
              if (rcache) {
                  int res = lfs_cache_cmp(lfs, rcache, NULL,
                          block, off, data, diff);
                  if (res < 0) {
                      return res;
                  }
  
                  if (!res) {
                      return LFS_ERR_CORRUPT;
                  }
              }
  
              data += diff;
              off += diff;
              size -= diff;
              continue;
          }
  
          // prepare pcache, first condition can no longer fail
          pcache->block = block;
          pcache->off = off - (off % lfs->cfg->prog_size);
      }
  
      return 0;
  }
  
  
  /// General lfs block device operations ///
  static int lfs_bd_read(lfs_t *lfs, lfs_block_t block,
          lfs_off_t off, void *buffer, lfs_size_t size) {
      // if we ever do more than writes to alternating pairs,
      // this may need to consider pcache
      return lfs_cache_read(lfs, &lfs->rcache, NULL,
              block, off, buffer, size);
  }
  
  static int lfs_bd_prog(lfs_t *lfs, lfs_block_t block,
          lfs_off_t off, const void *buffer, lfs_size_t size) {
      return lfs_cache_prog(lfs, &lfs->pcache, NULL,
              block, off, buffer, size);
  }
  
  static int lfs_bd_cmp(lfs_t *lfs, lfs_block_t block,
          lfs_off_t off, const void *buffer, lfs_size_t size) {
      return lfs_cache_cmp(lfs, &lfs->rcache, NULL, block, off, buffer, size);
  }
  
  static int lfs_bd_crc(lfs_t *lfs, lfs_block_t block,
          lfs_off_t off, lfs_size_t size, uint32_t *crc) {
      return lfs_cache_crc(lfs, &lfs->rcache, NULL, block, off, size, crc);
  }
  
  static int lfs_bd_erase(lfs_t *lfs, lfs_block_t block) {
      return lfs->cfg->erase(lfs->cfg, block);
  }
  
  static int lfs_bd_sync(lfs_t *lfs) {
      lfs->rcache.block = 0xffffffff;
  
      int err = lfs_cache_flush(lfs, &lfs->pcache, NULL);
      if (err) {
          return err;
      }
  
      return lfs->cfg->sync(lfs->cfg);
  }
  
  
  /// Internal operations predeclared here ///
  int lfs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data);
  static int lfs_pred(lfs_t *lfs, const lfs_block_t dir[2], lfs_dir_t *pdir);
  static int lfs_parent(lfs_t *lfs, const lfs_block_t dir[2],
          lfs_dir_t *parent, lfs_entry_t *entry);
  static int lfs_moved(lfs_t *lfs, const void *e);
  static int lfs_relocate(lfs_t *lfs,
          const lfs_block_t oldpair[2], const lfs_block_t newpair[2]);
  int lfs_deorphan(lfs_t *lfs);
  
  
  /// Block allocator ///
  static int lfs_alloc_lookahead(void *p, lfs_block_t block) {
      lfs_t *lfs = p;
  
      lfs_block_t off = (((lfs_soff_t)(block - lfs->free.begin)
                  % (lfs_soff_t)(lfs->cfg->block_count))
              + lfs->cfg->block_count) % lfs->cfg->block_count;
  
      if (off < lfs->free.size) {
          lfs->free.buffer[off / 32] |= 1U << (off % 32);
      }
  
      return 0;
  }
  
  static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) {
      while (true) {
          while (lfs->free.off != lfs->free.size) {
              lfs_block_t off = lfs->free.off;
              lfs->free.off += 1;
  
              if (!(lfs->free.buffer[off / 32] & (1U << (off % 32)))) {
                  // found a free block
                  *block = (lfs->free.begin + off) % lfs->cfg->block_count;
                  return 0;
              }
          }
  
          // check if we have looked at all blocks since last ack
          if (lfs->free.off == lfs->free.ack - lfs->free.begin) {
              LFS_WARN("No more free space %d", lfs->free.off + lfs->free.begin);
              return LFS_ERR_NOSPC;
          }
  
          lfs->free.begin += lfs->free.size;
          lfs->free.size = lfs_min(lfs->cfg->lookahead,
                  lfs->free.ack - lfs->free.begin);
          lfs->free.off = 0;
  
          // find mask of free blocks from tree
          memset(lfs->free.buffer, 0, lfs->cfg->lookahead/8);
          int err = lfs_traverse(lfs, lfs_alloc_lookahead, lfs);
          if (err) {
              return err;
          }
      }
  }
  
  static void lfs_alloc_ack(lfs_t *lfs) {
      lfs->free.ack = lfs->free.off-1 + lfs->free.begin + lfs->cfg->block_count;
  }
  
  
  /// Metadata pair and directory operations ///
  static inline void lfs_pairswap(lfs_block_t pair[2]) {
      lfs_block_t t = pair[0];
      pair[0] = pair[1];
      pair[1] = t;
  }
  
  static inline bool lfs_pairisnull(const lfs_block_t pair[2]) {
      return pair[0] == 0xffffffff || pair[1] == 0xffffffff;
  }
  
  static inline int lfs_paircmp(
          const lfs_block_t paira[2],
          const lfs_block_t pairb[2]) {
      return !(paira[0] == pairb[0] || paira[1] == pairb[1] ||
               paira[0] == pairb[1] || paira[1] == pairb[0]);
  }
  
  static inline bool lfs_pairsync(
          const lfs_block_t paira[2],
          const lfs_block_t pairb[2]) {
      return (paira[0] == pairb[0] && paira[1] == pairb[1]) ||
             (paira[0] == pairb[1] && paira[1] == pairb[0]);
  }
  
  static inline lfs_size_t lfs_entry_size(const lfs_entry_t *entry) {
      return 4 + entry->d.elen + entry->d.alen + entry->d.nlen;
  }
  
  static int lfs_dir_alloc(lfs_t *lfs, lfs_dir_t *dir) {
      // allocate pair of dir blocks
      for (int i = 0; i < 2; i++) {
          int err = lfs_alloc(lfs, &dir->pair[i]);
          if (err) {
              return err;
          }
      }
  
      // rather than clobbering one of the blocks we just pretend
      // the revision may be valid
      int err = lfs_bd_read(lfs, dir->pair[0], 0, &dir->d.rev, 4);
      if (err) {
          return err;
      }
  
      // set defaults
      dir->d.rev += 1;
      dir->d.size = sizeof(dir->d)+4;
      dir->d.tail[0] = 0xffffffff;
      dir->d.tail[1] = 0xffffffff;
      dir->off = sizeof(dir->d);
  
      // don't write out yet, let caller take care of that
      return 0;
  }
  
  static int lfs_dir_fetch(lfs_t *lfs,
          lfs_dir_t *dir, const lfs_block_t pair[2]) {
      // copy out pair, otherwise may be aliasing dir
      const lfs_block_t tpair[2] = {pair[0], pair[1]};
      bool valid = false;
  
      // check both blocks for the most recent revision
      for (int i = 0; i < 2; i++) {
          struct lfs_disk_dir test;
          int err = lfs_bd_read(lfs, tpair[i], 0, &test, sizeof(test));
          if (err) {
              return err;
          }
  
          if (valid && lfs_scmp(test.rev, dir->d.rev) < 0) {
              continue;
          }
  
          if ((0x7fffffff & test.size) < sizeof(test)+4 ||
              (0x7fffffff & test.size) > lfs->cfg->block_size) {
              continue;
          }
  
          uint32_t crc = 0xffffffff;
          lfs_crc(&crc, &test, sizeof(test));
          err = lfs_bd_crc(lfs, tpair[i], sizeof(test),
                  (0x7fffffff & test.size) - sizeof(test), &crc);
          if (err) {
              return err;
          }
  
          if (crc != 0) {
              continue;
          }
  
          valid = true;
  
          // setup dir in case it's valid
          dir->pair[0] = tpair[(i+0) % 2];
          dir->pair[1] = tpair[(i+1) % 2];
          dir->off = sizeof(dir->d);
          dir->d = test;
      }
  
      if (!valid) {
          LFS_ERROR("Corrupted dir pair at %d %d", tpair[0], tpair[1]);
          return LFS_ERR_CORRUPT;
      }
  
      return 0;
  }
  
  struct lfs_region {
      lfs_off_t oldoff;
      lfs_size_t oldlen;
      const void *newdata;
      lfs_size_t newlen;
  };
  
  static int lfs_dir_commit(lfs_t *lfs, lfs_dir_t *dir,
          const struct lfs_region *regions, int count) {
      // increment revision count
      dir->d.rev += 1;
  
      // keep pairs in order such that pair[0] is most recent
      lfs_pairswap(dir->pair);
      for (int i = 0; i < count; i++) {
          dir->d.size += regions[i].newlen - regions[i].oldlen;
      }
  
      const lfs_block_t oldpair[2] = {dir->pair[0], dir->pair[1]};
      bool relocated = false;
  
      while (true) {
          if (true) {
              int err = lfs_bd_erase(lfs, dir->pair[0]);
              if (err) {
                  if (err == LFS_ERR_CORRUPT) {
                      goto relocate;
                  }
                  return err;
              }
  
              uint32_t crc = 0xffffffff;
              lfs_crc(&crc, &dir->d, sizeof(dir->d));
              err = lfs_bd_prog(lfs, dir->pair[0], 0, &dir->d, sizeof(dir->d));
              if (err) {
                  if (err == LFS_ERR_CORRUPT) {
                      goto relocate;
                  }
                  return err;
              }
  
              int i = 0;
              lfs_off_t oldoff = sizeof(dir->d);
              lfs_off_t newoff = sizeof(dir->d);
              while (newoff < (0x7fffffff & dir->d.size)-4) {
                  if (i < count && regions[i].oldoff == oldoff) {
                      lfs_crc(&crc, regions[i].newdata, regions[i].newlen);
                      err = lfs_bd_prog(lfs, dir->pair[0],
                              newoff, regions[i].newdata, regions[i].newlen);
                      if (err) {
                          if (err == LFS_ERR_CORRUPT) {
                              goto relocate;
                          }
                          return err;
                      }
  
                      oldoff += regions[i].oldlen;
                      newoff += regions[i].newlen;
                      i += 1;
                  } else {
                      uint8_t data;
                      err = lfs_bd_read(lfs, oldpair[1], oldoff, &data, 1);
                      if (err) {
                          return err;
                      }
  
                      lfs_crc(&crc, &data, 1);
                      err = lfs_bd_prog(lfs, dir->pair[0], newoff, &data, 1);
                      if (err) {
                          if (err == LFS_ERR_CORRUPT) {
                              goto relocate;
                          }
                          return err;
                      }
  
                      oldoff += 1;
                      newoff += 1;
                  }
              }
  
              err = lfs_bd_prog(lfs, dir->pair[0], newoff, &crc, 4);
              if (err) {
                  if (err == LFS_ERR_CORRUPT) {
                      goto relocate;
                  }
                  return err;
              }
  
              err = lfs_bd_sync(lfs);
              if (err) {
                  if (err == LFS_ERR_CORRUPT) {
                      goto relocate;
                  }
                  return err;
              }
  
              // successful commit, check checksum to make sure
              uint32_t ncrc = 0xffffffff;
              err = lfs_bd_crc(lfs, dir->pair[0], 0,
                      (0x7fffffff & dir->d.size)-4, &ncrc);
              if (err) {
                  return err;
              }
  
              if (ncrc != crc) {
                  goto relocate;
              }
          }
  
          break;
  relocate:
          //commit was corrupted
          LFS_DEBUG("Bad block at %d", dir->pair[0]);
  
          // drop caches and prepare to relocate block
          relocated = true;
          lfs->pcache.block = 0xffffffff;
  
          // can't relocate superblock, filesystem is now frozen
          if (lfs_paircmp(oldpair, (const lfs_block_t[2]){0, 1}) == 0) {
              LFS_WARN("Superblock %d has become unwritable", oldpair[0]);
              return LFS_ERR_CORRUPT;
          }
  
          // relocate half of pair
          int err = lfs_alloc(lfs, &dir->pair[0]);
          if (err) {
              return err;
          }
      }
  
      if (relocated) {
          // update references if we relocated
          LFS_DEBUG("Relocating %d %d to %d %d",
                  oldpair[0], oldpair[1], dir->pair[0], dir->pair[1]);
          int err = lfs_relocate(lfs, oldpair, dir->pair);
          if (err) {
              return err;
          }
      }
  
      // shift over any directories that are affected
      for (lfs_dir_t *d = lfs->dirs; d; d = d->next) {
          if (lfs_paircmp(d->pair, dir->pair) == 0) {
              d->pair[0] = dir->pair[0];
              d->pair[1] = dir->pair[1];
          }
      }
  
      return 0;
  }
  
  static int lfs_dir_update(lfs_t *lfs, lfs_dir_t *dir,
          const lfs_entry_t *entry, const void *data) {
      return lfs_dir_commit(lfs, dir, (struct lfs_region[]){
              {entry->off, sizeof(entry->d), &entry->d, sizeof(entry->d)},
              {entry->off+sizeof(entry->d), entry->d.nlen, data, entry->d.nlen}
          }, data ? 2 : 1);
  }
  
  static int lfs_dir_append(lfs_t *lfs, lfs_dir_t *dir,
          lfs_entry_t *entry, const void *data) {
      // check if we fit, if top bit is set we do not and move on
      while (true) {
          if (dir->d.size + lfs_entry_size(entry) <= lfs->cfg->block_size) {
              entry->off = dir->d.size - 4;
              return lfs_dir_commit(lfs, dir, (struct lfs_region[]){
                      {entry->off, 0, &entry->d, sizeof(entry->d)},
                      {entry->off, 0, data, entry->d.nlen}
                  }, 2);
          }
  
          // we need to allocate a new dir block
          if (!(0x80000000 & dir->d.size)) {
              lfs_dir_t newdir;
              int err = lfs_dir_alloc(lfs, &newdir);
              if (err) {
                  return err;
              }
  
              newdir.d.tail[0] = dir->d.tail[0];
              newdir.d.tail[1] = dir->d.tail[1];
              entry->off = newdir.d.size - 4;
              err = lfs_dir_commit(lfs, &newdir, (struct lfs_region[]){
                      {entry->off, 0, &entry->d, sizeof(entry->d)},
                      {entry->off, 0, data, entry->d.nlen}
                  }, 2);
              if (err) {
                  return err;
              }
  
              dir->d.size |= 0x80000000;
              dir->d.tail[0] = newdir.pair[0];
              dir->d.tail[1] = newdir.pair[1];
              return lfs_dir_commit(lfs, dir, NULL, 0);
          }
  
          int err = lfs_dir_fetch(lfs, dir, dir->d.tail);
          if (err) {
              return err;
          }
      }
  }
  
  static int lfs_dir_remove(lfs_t *lfs, lfs_dir_t *dir, lfs_entry_t *entry) {
      // check if we should just drop the directory block
      if ((dir->d.size & 0x7fffffff) == sizeof(dir->d)+4
              + lfs_entry_size(entry)) {
          lfs_dir_t pdir;
          int res = lfs_pred(lfs, dir->pair, &pdir);
          if (res < 0) {
              return res;
          }
  
          if (pdir.d.size & 0x80000000) {
              pdir.d.size &= dir->d.size | 0x7fffffff;
              pdir.d.tail[0] = dir->d.tail[0];
              pdir.d.tail[1] = dir->d.tail[1];
              return lfs_dir_commit(lfs, &pdir, NULL, 0);
          }
      }
  
      // shift out the entry
      int err = lfs_dir_commit(lfs, dir, (struct lfs_region[]){
              {entry->off, lfs_entry_size(entry), NULL, 0},
          }, 1);
      if (err) {
          return err;
      }
  
      // shift over any files/directories that are affected
      for (lfs_file_t *f = lfs->files; f; f = f->next) {
          if (lfs_paircmp(f->pair, dir->pair) == 0) {
              if (f->poff == entry->off) {
                  f->pair[0] = 0xffffffff;
                  f->pair[1] = 0xffffffff;
              } else if (f->poff > entry->off) {
                  f->poff -= lfs_entry_size(entry);
              }
          }
      }
  
      for (lfs_dir_t *d = lfs->dirs; d; d = d->next) {
          if (lfs_paircmp(d->pair, dir->pair) == 0) {
              if (d->off > entry->off) {
                  d->off -= lfs_entry_size(entry);
                  d->pos -= lfs_entry_size(entry);
              }
          }
      }
  
      return 0;
  }
  
  static int lfs_dir_next(lfs_t *lfs, lfs_dir_t *dir, lfs_entry_t *entry) {
      while (dir->off + sizeof(entry->d) > (0x7fffffff & dir->d.size)-4) {
          if (!(0x80000000 & dir->d.size)) {
              entry->off = dir->off;
              return LFS_ERR_NOENT;
          }
  
          int err = lfs_dir_fetch(lfs, dir, dir->d.tail);
          if (err) {
              return err;
          }
  
          dir->off = sizeof(dir->d);
          dir->pos += sizeof(dir->d) + 4;
      }
  
      int err = lfs_bd_read(lfs, dir->pair[0], dir->off,
              &entry->d, sizeof(entry->d));
      if (err) {
          return err;
      }
  
      entry->off = dir->off;
      dir->off += lfs_entry_size(entry);
      dir->pos += lfs_entry_size(entry);
      return 0;
  }
  
  static int lfs_dir_find(lfs_t *lfs, lfs_dir_t *dir,
          lfs_entry_t *entry, const char **path) {
      const char *pathname = *path;
      size_t pathlen;
  
      while (true) {
      nextname:
          // skip slashes
          pathname += strspn(pathname, "/");
          pathlen = strcspn(pathname, "/");
  
          // skip '.' and root '..'
          if ((pathlen == 1 && memcmp(pathname, ".", 1) == 0) ||
              (pathlen == 2 && memcmp(pathname, "..", 2) == 0)) {
              pathname += pathlen;
              goto nextname;
          }
  
          // skip if matched by '..' in name
          const char *suffix = pathname + pathlen;
          size_t sufflen;
          int depth = 1;
          while (true) {
              suffix += strspn(suffix, "/");
              sufflen = strcspn(suffix, "/");
              if (sufflen == 0) {
                  break;
              }
  
              if (sufflen == 2 && memcmp(suffix, "..", 2) == 0) {
                  depth -= 1;
                  if (depth == 0) {
                      pathname = suffix + sufflen;
                      goto nextname;
                  }
              } else {
                  depth += 1;
              }
  
              suffix += sufflen;
          }
  
          // update what we've found
          *path = pathname;
  
          // find path
          while (true) {
              int err = lfs_dir_next(lfs, dir, entry);
              if (err) {
                  return err;
              }
  
              if (((0x7f & entry->d.type) != LFS_TYPE_REG &&
                   (0x7f & entry->d.type) != LFS_TYPE_DIR) ||
                  entry->d.nlen != pathlen) {
                  continue;
              }
  
              int res = lfs_bd_cmp(lfs, dir->pair[0],
                      entry->off + 4+entry->d.elen+entry->d.alen,
                      pathname, pathlen);
              if (res < 0) {
                  return res;
              }
  
              // found match
              if (res) {
                  break;
              }
          }
  
          // check that entry has not been moved
          if (entry->d.type & 0x80) {
              int moved = lfs_moved(lfs, &entry->d.u);
              if (moved < 0 || moved) {
                  return (moved < 0) ? moved : LFS_ERR_NOENT;
              }
  
              entry->d.type &= ~0x80;
          }
  
          pathname += pathlen;
          pathname += strspn(pathname, "/");
          if (pathname[0] == '\0') {
              return 0;
          }
  
          // continue on if we hit a directory
          if (entry->d.type != LFS_TYPE_DIR) {
              return LFS_ERR_NOTDIR;
          }
  
          int err = lfs_dir_fetch(lfs, dir, entry->d.u.dir);
          if (err) {
              return err;
          }
      }
  }
  
  
  /// Top level directory operations ///
  int lfs_mkdir(lfs_t *lfs, const char *path) {
      // deorphan if we haven't yet, needed at most once after poweron
      if (!lfs->deorphaned) {
          int err = lfs_deorphan(lfs);
          if (err) {
              return err;
          }
      }
  
      // fetch parent directory
      lfs_dir_t cwd;
      int err = lfs_dir_fetch(lfs, &cwd, lfs->root);
      if (err) {
          return err;
      }
  
      lfs_entry_t entry;
      err = lfs_dir_find(lfs, &cwd, &entry, &path);
      if (err != LFS_ERR_NOENT || strchr(path, '/') != NULL) {
          return err ? err : LFS_ERR_EXIST;
      }
  
      // build up new directory
      lfs_alloc_ack(lfs);
  
      lfs_dir_t dir;
      err = lfs_dir_alloc(lfs, &dir);
      if (err) {
          return err;
      }
      dir.d.tail[0] = cwd.d.tail[0];
      dir.d.tail[1] = cwd.d.tail[1];
  
      err = lfs_dir_commit(lfs, &dir, NULL, 0);
      if (err) {
          return err;
      }
  
      entry.d.type = LFS_TYPE_DIR;
      entry.d.elen = sizeof(entry.d) - 4;
      entry.d.alen = 0;
      entry.d.nlen = strlen(path);
      entry.d.u.dir[0] = dir.pair[0];
      entry.d.u.dir[1] = dir.pair[1];
  
      cwd.d.tail[0] = dir.pair[0];
      cwd.d.tail[1] = dir.pair[1];
  
      err = lfs_dir_append(lfs, &cwd, &entry, path);
      if (err) {
          return err;
      }
  
      lfs_alloc_ack(lfs);
      return 0;
  }
  
  int lfs_dir_open(lfs_t *lfs, lfs_dir_t *dir, const char *path) {
      dir->pair[0] = lfs->root[0];
      dir->pair[1] = lfs->root[1];
  
      int err = lfs_dir_fetch(lfs, dir, dir->pair);
      if (err) {
          return err;
      }
  
      // check for root, can only be something like '/././../.'
      if (strspn(path, "/.") == strlen(path)) {
          dir->head[0] = dir->pair[0];
          dir->head[1] = dir->pair[1];
          dir->pos = sizeof(dir->d) - 2;
          dir->off = sizeof(dir->d);
          return 0;
      }
  
      lfs_entry_t entry;
      err = lfs_dir_find(lfs, dir, &entry, &path);
      if (err) {
          return err;
      } else if (entry.d.type != LFS_TYPE_DIR) {
          return LFS_ERR_NOTDIR;
      }
  
      err = lfs_dir_fetch(lfs, dir, entry.d.u.dir);
      if (err) {
          return err;
      }
  
      // setup head dir
      // special offset for '.' and '..'
      dir->head[0] = dir->pair[0];
      dir->head[1] = dir->pair[1];
      dir->pos = sizeof(dir->d) - 2;
      dir->off = sizeof(dir->d);
  
      // add to list of directories
      dir->next = lfs->dirs;
      lfs->dirs = dir;
  
      return 0;
  }
  
  int lfs_dir_close(lfs_t *lfs, lfs_dir_t *dir) {
      // remove from list of directories
      for (lfs_dir_t **p = &lfs->dirs; *p; p = &(*p)->next) {
          if (*p == dir) {
              *p = dir->next;
              break;
          }
      }
  
      return 0;
  }
  
  int lfs_dir_read(lfs_t *lfs, lfs_dir_t *dir, struct lfs_info *info) {
      memset(info, 0, sizeof(*info));
  
      // special offset for '.' and '..'
      if (dir->pos == sizeof(dir->d) - 2) {
          info->type = LFS_TYPE_DIR;
          strcpy(info->name, ".");
          dir->pos += 1;
          return 1;
      } else if (dir->pos == sizeof(dir->d) - 1) {
          info->type = LFS_TYPE_DIR;
          strcpy(info->name, "..");
          dir->pos += 1;
          return 1;
      }
  
      lfs_entry_t entry;
      while (true) {
          int err = lfs_dir_next(lfs, dir, &entry);
          if (err) {
              return (err == LFS_ERR_NOENT) ? 0 : err;
          }
  
          if ((0x7f & entry.d.type) != LFS_TYPE_REG &&
              (0x7f & entry.d.type) != LFS_TYPE_DIR) {
              continue;
          }
  
          // check that entry has not been moved
          if (entry.d.type & 0x80) {
              int moved = lfs_moved(lfs, &entry.d.u);
              if (moved < 0) {
                  return moved;
              }
  
              if (moved) {
                  continue;
              }
  
              entry.d.type &= ~0x80;
          }
  
          break;
      }
  
      info->type = entry.d.type;
      if (info->type == LFS_TYPE_REG) {
          info->size = entry.d.u.file.size;
      }
  
      int err = lfs_bd_read(lfs, dir->pair[0],
              entry.off + 4+entry.d.elen+entry.d.alen,
              info->name, entry.d.nlen);
      if (err) {
          return err;
      }
  
      return 1;
  }
  
  int lfs_dir_seek(lfs_t *lfs, lfs_dir_t *dir, lfs_off_t off) {
      // simply walk from head dir
      int err = lfs_dir_rewind(lfs, dir);
      if (err) {
          return err;
      }
      dir->pos = off;
  
      while (off > (0x7fffffff & dir->d.size)) {
          off -= 0x7fffffff & dir->d.size;
          if (!(0x80000000 & dir->d.size)) {
              return LFS_ERR_INVAL;
          }
  
          err = lfs_dir_fetch(lfs, dir, dir->d.tail);
          if (err) {
              return err;
          }
      }
  
      dir->off = off;
      return 0;
  }
  
  lfs_soff_t lfs_dir_tell(lfs_t *lfs, lfs_dir_t *dir) {
      (void)lfs;
      return dir->pos;
  }
  
  int lfs_dir_rewind(lfs_t *lfs, lfs_dir_t *dir) {
      // reload the head dir
      int err = lfs_dir_fetch(lfs, dir, dir->head);
      if (err) {
          return err;
      }
  
      dir->pair[0] = dir->head[0];
      dir->pair[1] = dir->head[1];
      dir->pos = sizeof(dir->d) - 2;
      dir->off = sizeof(dir->d);
      return 0;
  }
  
  
  /// File index list operations ///
  static int lfs_ctz_index(lfs_t *lfs, lfs_off_t *off) {
      lfs_off_t size = *off;
      lfs_off_t b = lfs->cfg->block_size - 2*4;
      lfs_off_t i = size / b;
      if (i == 0) {
          return 0;
      }
  
      i = (size - 4*(lfs_popc(i-1)+2)) / b;
      *off = size - b*i - 4*lfs_popc(i);
      return i;
  }
  
  static int lfs_ctz_find(lfs_t *lfs,
          lfs_cache_t *rcache, const lfs_cache_t *pcache,
          lfs_block_t head, lfs_size_t size,
          lfs_size_t pos, lfs_block_t *block, lfs_off_t *off) {
      if (size == 0) {
          *block = 0xffffffff;
          *off = 0;
          return 0;
      }
  
      lfs_off_t current = lfs_ctz_index(lfs, &(lfs_off_t){size-1});
      lfs_off_t target = lfs_ctz_index(lfs, &pos);
  
      while (current > target) {
          lfs_size_t skip = lfs_min(
                  lfs_npw2(current-target+1) - 1,
                  lfs_ctz(current));
  
          int err = lfs_cache_read(lfs, rcache, pcache, head, 4*skip, &head, 4);
          if (err) {
              return err;
          }
  
          assert(head >= 2 && head <= lfs->cfg->block_count);
          current -= 1 << skip;
      }
  
      *block = head;
      *off = pos;
      return 0;
  }
  
  static int lfs_ctz_extend(lfs_t *lfs,
          lfs_cache_t *rcache, lfs_cache_t *pcache,
          lfs_block_t head, lfs_size_t size,
          lfs_block_t *block, lfs_off_t *off) {
      while (true) {
          // go ahead and grab a block
          lfs_block_t nblock;
          int err = lfs_alloc(lfs, &nblock);
          if (err) {
              return err;
          }
          assert(nblock >= 2 && nblock <= lfs->cfg->block_count);
  
          if (true) {
              err = lfs_bd_erase(lfs, nblock);
              if (err) {
                  if (err == LFS_ERR_CORRUPT) {
                      goto relocate;
                  }
                  return err;
              }
  
              if (size == 0) {
                  *block = nblock;
                  *off = 0;
                  return 0;
              }
  
              size -= 1;
              lfs_off_t index = lfs_ctz_index(lfs, &size);
              size += 1;
  
              // just copy out the last block if it is incomplete
              if (size != lfs->cfg->block_size) {
                  for (lfs_off_t i = 0; i < size; i++) {
                      uint8_t data;
                      err = lfs_cache_read(lfs, rcache, NULL,
                              head, i, &data, 1);
                      if (err) {
                          return err;
                      }
  
                      err = lfs_cache_prog(lfs, pcache, rcache,
                              nblock, i, &data, 1);
                      if (err) {
                          if (err == LFS_ERR_CORRUPT) {
                              goto relocate;
                          }
                          return err;
                      }
                  }
  
                  *block = nblock;
                  *off = size;
                  return 0;
              }
  
              // append block
              index += 1;
              lfs_size_t skips = lfs_ctz(index) + 1;
  
              for (lfs_off_t i = 0; i < skips; i++) {
                  err = lfs_cache_prog(lfs, pcache, rcache,
                          nblock, 4*i, &head, 4);
                  if (err) {
                      if (err == LFS_ERR_CORRUPT) {
                          goto relocate;
                      }
                      return err;
                  }
  
                  if (i != skips-1) {
                      err = lfs_cache_read(lfs, rcache, NULL,
                              head, 4*i, &head, 4);
                      if (err) {
                          return err;
                      }
                  }
  
                  assert(head >= 2 && head <= lfs->cfg->block_count);
              }
  
              *block = nblock;
              *off = 4*skips;
              return 0;
          }
  
  relocate:
          LFS_DEBUG("Bad block at %d", nblock);
  
          // just clear cache and try a new block
          pcache->block = 0xffffffff;
      }
  }
  
  static int lfs_ctz_traverse(lfs_t *lfs,
          lfs_cache_t *rcache, const lfs_cache_t *pcache,
          lfs_block_t head, lfs_size_t size,
          int (*cb)(void*, lfs_block_t), void *data) {
      if (size == 0) {
          return 0;
      }
  
      lfs_off_t index = lfs_ctz_index(lfs, &(lfs_off_t){size-1});
  
      while (true) {
          int err = cb(data, head);
          if (err) {
              return err;
          }
  
          if (index == 0) {
              return 0;
          }
  
          lfs_block_t heads[2];
          int count = 2 - (index & 1);
          err = lfs_cache_read(lfs, rcache, pcache, head, 0, &heads, count*4);
          if (err) {
              return err;
          }
  
          for (int i = 0; i < count-1; i++) {
              err = cb(data, heads[i]);
              if (err) {
                  return err;
              }
          }
  
          head = heads[count-1];
          index -= count;
      }
  }
  
  
  /// Top level file operations ///
  int lfs_file_open(lfs_t *lfs, lfs_file_t *file,
          const char *path, int flags) {
      // deorphan if we haven't yet, needed at most once after poweron
      if ((flags & 3) != LFS_O_RDONLY && !lfs->deorphaned) {
          int err = lfs_deorphan(lfs);
          if (err) {
              return err;
          }
      }
  
      // allocate entry for file if it doesn't exist
      lfs_dir_t cwd;
      int err = lfs_dir_fetch(lfs, &cwd, lfs->root);
      if (err) {
          return err;
      }
  
      lfs_entry_t entry;
      err = lfs_dir_find(lfs, &cwd, &entry, &path);
      if (err && (err != LFS_ERR_NOENT || strchr(path, '/') != NULL)) {
          return err;
      }
  
      if (err == LFS_ERR_NOENT) {
          if (!(flags & LFS_O_CREAT)) {
              return LFS_ERR_NOENT;
          }
  
          // create entry to remember name
          entry.d.type = LFS_TYPE_REG;
          entry.d.elen = sizeof(entry.d) - 4;
          entry.d.alen = 0;
          entry.d.nlen = strlen(path);
          entry.d.u.file.head = 0xffffffff;
          entry.d.u.file.size = 0;
          err = lfs_dir_append(lfs, &cwd, &entry, path);
          if (err) {
              return err;
          }
      } else if (entry.d.type == LFS_TYPE_DIR) {
          return LFS_ERR_ISDIR;
      } else if (flags & LFS_O_EXCL) {
          return LFS_ERR_EXIST;
      }
  
      // setup file struct
      file->pair[0] = cwd.pair[0];
      file->pair[1] = cwd.pair[1];
      file->poff = entry.off;
      file->head = entry.d.u.file.head;
      file->size = entry.d.u.file.size;
      file->flags = flags;
      file->pos = 0;
  
      if (flags & LFS_O_TRUNC) {
          if (file->size != 0) {
              file->flags |= LFS_F_DIRTY;
          }
          file->head = 0xffffffff;
          file->size = 0;
      }
  
      // allocate buffer if needed
      file->cache.block = 0xffffffff;
      if (lfs->cfg->file_buffer) {
          file->cache.buffer = lfs->cfg->file_buffer;
      } else if ((file->flags & 3) == LFS_O_RDONLY) {
          file->cache.buffer = malloc(lfs->cfg->read_size);
          if (!file->cache.buffer) {
              return LFS_ERR_NOMEM;
          }
      } else {
          file->cache.buffer = malloc(lfs->cfg->prog_size);
          if (!file->cache.buffer) {
              return LFS_ERR_NOMEM;
          }
      }
  
      // add to list of files
      file->next = lfs->files;
      lfs->files = file;
  
      return 0;
  }
  
  int lfs_file_close(lfs_t *lfs, lfs_file_t *file) {
      int err = lfs_file_sync(lfs, file);
  
      // remove from list of files
      for (lfs_file_t **p = &lfs->files; *p; p = &(*p)->next) {
          if (*p == file) {
              *p = file->next;
              break;
          }
      }
  
      // clean up memory
      if (!lfs->cfg->file_buffer) {
          free(file->cache.buffer);
      }
  
      return err;
  }
  
  static int lfs_file_relocate(lfs_t *lfs, lfs_file_t *file) {
  relocate:
      LFS_DEBUG("Bad block at %d", file->block);
  
      // just relocate what exists into new block
      lfs_block_t nblock;
      int err = lfs_alloc(lfs, &nblock);
      if (err) {
          return err;
      }
  
      err = lfs_bd_erase(lfs, nblock);
      if (err) {
          if (err == LFS_ERR_CORRUPT) {
              goto relocate;
          }
          return err;
      }
  
      // either read from dirty cache or disk
      for (lfs_off_t i = 0; i < file->off; i++) {
          uint8_t data;
          err = lfs_cache_read(lfs, &lfs->rcache, &file->cache,
                  file->block, i, &data, 1);
          if (err) {
              return err;
          }
  
          err = lfs_cache_prog(lfs, &lfs->pcache, &lfs->rcache,
                  nblock, i, &data, 1);
          if (err) {
              if (err == LFS_ERR_CORRUPT) {
                  goto relocate;
              }
              return err;
          }
      }
  
      // copy over new state of file
      memcpy(file->cache.buffer, lfs->pcache.buffer, lfs->cfg->prog_size);
      file->cache.block = lfs->pcache.block;
      file->cache.off = lfs->pcache.off;
      lfs->pcache.block = 0xffffffff;
  
      file->block = nblock;
      return 0;
  }
  
  static int lfs_file_flush(lfs_t *lfs, lfs_file_t *file) {
      if (file->flags & LFS_F_READING) {
          // just drop read cache
          file->cache.block = 0xffffffff;
          file->flags &= ~LFS_F_READING;
      }
  
      if (file->flags & LFS_F_WRITING) {
          lfs_off_t pos = file->pos;
  
          // copy over anything after current branch
          lfs_file_t orig = {
              .head = file->head,
              .size = file->size,
              .flags = LFS_O_RDONLY,
              .pos = file->pos,
              .cache = lfs->rcache,
          };
          lfs->rcache.block = 0xffffffff;
  
          while (file->pos < file->size) {
              // copy over a byte at a time, leave it up to caching
              // to make this efficient
              uint8_t data;
              lfs_ssize_t res = lfs_file_read(lfs, &orig, &data, 1);
              if (res < 0) {
                  return res;
              }
  
              res = lfs_file_write(lfs, file, &data, 1);
              if (res < 0) {
                  return res;
              }
  
              // keep our reference to the rcache in sync
              if (lfs->rcache.block != 0xffffffff) {
                  orig.cache.block = 0xffffffff;
                  lfs->rcache.block = 0xffffffff;
              }
          }
  
          // write out what we have
          while (true) {
              int err = lfs_cache_flush(lfs, &file->cache, &lfs->rcache);
              if (err) {
                  if (err == LFS_ERR_CORRUPT) {
                      goto relocate;
                  }
                  return err;
              }
  
              break;
  relocate:
              err = lfs_file_relocate(lfs, file);
              if (err) {
                  return err;
              }
          }
  
          // actual file updates
          file->head = file->block;
          file->size = file->pos;
          file->flags &= ~LFS_F_WRITING;
          file->flags |= LFS_F_DIRTY;
  
          file->pos = pos;
      }
  
      return 0;
  }
  
  int lfs_file_sync(lfs_t *lfs, lfs_file_t *file) {
      int err = lfs_file_flush(lfs, file);
      if (err) {
          return err;
      }
  
      if ((file->flags & LFS_F_DIRTY) &&
              !(file->flags & LFS_F_ERRED) &&
              !lfs_pairisnull(file->pair)) {
          // update dir entry
          lfs_dir_t cwd;
          err = lfs_dir_fetch(lfs, &cwd, file->pair);
          if (err) {
              return err;
          }
  
          lfs_entry_t entry = {.off = file->poff};
          err = lfs_bd_read(lfs, cwd.pair[0], entry.off,
                  &entry.d, sizeof(entry.d));
          if (err) {
              return err;
          }
  
          assert(entry.d.type == LFS_TYPE_REG);
          entry.d.u.file.head = file->head;
          entry.d.u.file.size = file->size;
  
          err = lfs_dir_update(lfs, &cwd, &entry, NULL);
          if (err) {
              return err;
          }
  
          file->flags &= ~LFS_F_DIRTY;
      }
  
      return 0;
  }
  
  lfs_ssize_t lfs_file_read(lfs_t *lfs, lfs_file_t *file,
          void *buffer, lfs_size_t size) {
      uint8_t *data = buffer;
      lfs_size_t nsize = size;
  
      if ((file->flags & 3) == LFS_O_WRONLY) {
          return LFS_ERR_BADF;
      }
  
      if (file->flags & LFS_F_WRITING) {
          // flush out any writes
          int err = lfs_file_flush(lfs, file);
          if (err) {
              return err;
          }
      }
  
      if (file->pos >= file->size) {
          // eof if past end
          return 0;
      }
  
      size = lfs_min(size, file->size - file->pos);
      nsize = size;
  
      while (nsize > 0) {
          // check if we need a new block
          if (!(file->flags & LFS_F_READING) ||
                  file->off == lfs->cfg->block_size) {
              int err = lfs_ctz_find(lfs, &file->cache, NULL,
                      file->head, file->size,
                      file->pos, &file->block, &file->off);
              if (err) {
                  return err;
              }
  
              file->flags |= LFS_F_READING;
          }
  
          // read as much as we can in current block
          lfs_size_t diff = lfs_min(nsize, lfs->cfg->block_size - file->off);
          int err = lfs_cache_read(lfs, &file->cache, NULL,
                  file->block, file->off, data, diff);
          if (err) {
              return err;
          }
  
          file->pos += diff;
          file->off += diff;
          data += diff;
          nsize -= diff;
      }
  
      return size;
  }
  
  lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file,
          const void *buffer, lfs_size_t size) {
      const uint8_t *data = buffer;
      lfs_size_t nsize = size;
  
      if ((file->flags & 3) == LFS_O_RDONLY) {
          return LFS_ERR_BADF;
      }
  
      if (file->flags & LFS_F_READING) {
          // drop any reads
          int err = lfs_file_flush(lfs, file);
          if (err) {
              return err;
          }
      }
  
      if ((file->flags & LFS_O_APPEND) && file->pos < file->size) {
          file->pos = file->size;
      }
  
      if (!(file->flags & LFS_F_WRITING) && file->pos > file->size) {
          // fill with zeros
          lfs_off_t pos = file->pos;
          file->pos = file->size;
  
          while (file->pos < pos) {
              lfs_ssize_t res = lfs_file_write(lfs, file, &(uint8_t){0}, 1);
              if (res < 0) {
                  return res;
              }
          }
      }
  
      while (nsize > 0) {
          // check if we need a new block
          if (!(file->flags & LFS_F_WRITING) ||
                  file->off == lfs->cfg->block_size) {
              if (!(file->flags & LFS_F_WRITING) && file->pos > 0) {
                  // find out which block we're extending from
                  int err = lfs_ctz_find(lfs, &file->cache, NULL,
                          file->head, file->size,
                          file->pos-1, &file->block, &file->off);
                  if (err) {
                      file->flags |= LFS_F_ERRED;
                      return err;
                  }
  
                  // mark cache as dirty since we may have read data into it
                  file->cache.block = 0xffffffff;
              }
  
              // extend file with new blocks
              lfs_alloc_ack(lfs);
              int err = lfs_ctz_extend(lfs, &lfs->rcache, &file->cache,
                      file->block, file->pos,
                      &file->block, &file->off);
              if (err) {
                  file->flags |= LFS_F_ERRED;
                  return err;
              }
  
              file->flags |= LFS_F_WRITING;
          }
  
          // program as much as we can in current block
          lfs_size_t diff = lfs_min(nsize, lfs->cfg->block_size - file->off);
          while (true) {
              int err = lfs_cache_prog(lfs, &file->cache, &lfs->rcache,
                      file->block, file->off, data, diff);
              if (err) {
                  if (err == LFS_ERR_CORRUPT) {
                      goto relocate;
                  }
                  file->flags |= LFS_F_ERRED;
                  return err;
              }
  
              break;
  relocate:
              err = lfs_file_relocate(lfs, file);
              if (err) {
                  file->flags |= LFS_F_ERRED;
                  return err;
              }
          }
  
          file->pos += diff;
          file->off += diff;
          data += diff;
          nsize -= diff;
  
          lfs_alloc_ack(lfs);
      }
  
      file->flags &= ~LFS_F_ERRED;
      return size;
  }
  
  lfs_soff_t lfs_file_seek(lfs_t *lfs, lfs_file_t *file,
          lfs_soff_t off, int whence) {
      // write out everything beforehand, may be noop if rdonly
      int err = lfs_file_flush(lfs, file);
      if (err) {
          return err;
      }
  
      // update pos
      if (whence == LFS_SEEK_SET) {
          file->pos = off;
      } else if (whence == LFS_SEEK_CUR) {
          if (off < 0 && (lfs_off_t)-off > file->pos) {
              return LFS_ERR_INVAL;
          }
  
          file->pos = file->pos + off;
      } else if (whence == LFS_SEEK_END) {
          if (off < 0 && (lfs_off_t)-off > file->size) {
              return LFS_ERR_INVAL;
          }
  
          file->pos = file->size + off;
      }
  
      return file->pos;
  }
  
  int lfs_file_truncate(lfs_t *lfs, lfs_file_t *file, lfs_off_t size) {
      if ((file->flags & 3) == LFS_O_RDONLY) {
          return LFS_ERR_BADF;
      }
  
      lfs_off_t oldsize = lfs_file_size(lfs, file);
      if (size < oldsize) {
          // need to flush since directly changing metadata
          int err = lfs_file_flush(lfs, file);
          if (err) {
              return err;
          }
  
          // lookup new head in ctz skip list
          err = lfs_ctz_find(lfs, &file->cache, NULL,
                  file->head, file->size,
                  size, &file->head, &(lfs_off_t){0});
          if (err) {
              return err;
          }
  
          file->size = size;
          file->flags |= LFS_F_DIRTY;
      } else if (size > oldsize) {
          lfs_off_t pos = file->pos;
  
          // flush+seek if not already at end
          if (file->pos != oldsize) {
              int err = lfs_file_seek(lfs, file, 0, SEEK_END);
              if (err < 0) {
                  return err;
              }
          }
  
          // fill with zeros
          while (file->pos < size) {
              lfs_ssize_t res = lfs_file_write(lfs, file, &(uint8_t){0}, 1);
              if (res < 0) {
                  return res;
              }
          }
  
          // restore pos
          int err = lfs_file_seek(lfs, file, pos, LFS_SEEK_SET);
          if (err < 0) {
              return err;
          }
      }
  
      return 0;
  }
  
  lfs_soff_t lfs_file_tell(lfs_t *lfs, lfs_file_t *file) {
      (void)lfs;
      return file->pos;
  }
  
  int lfs_file_rewind(lfs_t *lfs, lfs_file_t *file) {
      lfs_soff_t res = lfs_file_seek(lfs, file, 0, LFS_SEEK_SET);
      if (res < 0) {
          return res;
      }
  
      return 0;
  }
  
  lfs_soff_t lfs_file_size(lfs_t *lfs, lfs_file_t *file) {
      (void)lfs;
      if (file->flags & LFS_F_WRITING) {
          return lfs_max(file->pos, file->size);
      } else {
          return file->size;
      }
  }
  
  
  /// General fs operations ///
  int lfs_stat(lfs_t *lfs, const char *path, struct lfs_info *info) {
      // check for root, can only be something like '/././../.'
      if (strspn(path, "/.") == strlen(path)) {
          memset(info, 0, sizeof(*info));
          info->type = LFS_TYPE_DIR;
          strcpy(info->name, "/");
          return 0;
      }
  
      lfs_dir_t cwd;
      int err = lfs_dir_fetch(lfs, &cwd, lfs->root);
      if (err) {
          return err;
      }
  
      lfs_entry_t entry;
      err = lfs_dir_find(lfs, &cwd, &entry, &path);
      if (err) {
          return err;
      }
  
      memset(info, 0, sizeof(*info));
      info->type = entry.d.type;
      if (info->type == LFS_TYPE_REG) {
          info->size = entry.d.u.file.size;
      }
  
      err = lfs_bd_read(lfs, cwd.pair[0],
              entry.off + 4+entry.d.elen+entry.d.alen,
              info->name, entry.d.nlen);
      if (err) {
          return err;
      }
  
      return 0;
  }
  
  int lfs_remove(lfs_t *lfs, const char *path) {
      // deorphan if we haven't yet, needed at most once after poweron
      if (!lfs->deorphaned) {
          int err = lfs_deorphan(lfs);
          if (err) {
              return err;
          }
      }
  
      lfs_dir_t cwd;
      int err = lfs_dir_fetch(lfs, &cwd, lfs->root);
      if (err) {
          return err;
      }
  
      lfs_entry_t entry;
      err = lfs_dir_find(lfs, &cwd, &entry, &path);
      if (err) {
          return err;
      }
  
      lfs_dir_t dir;
      if (entry.d.type == LFS_TYPE_DIR) {
          // must be empty before removal, checking size
          // without masking top bit checks for any case where
          // dir is not empty
          err = lfs_dir_fetch(lfs, &dir, entry.d.u.dir);
          if (err) {
              return err;
          } else if (dir.d.size != sizeof(dir.d)+4) {
              return LFS_ERR_NOTEMPTY;
          }
      }
  
      // remove the entry
      err = lfs_dir_remove(lfs, &cwd, &entry);
      if (err) {
          return err;
      }
  
      // if we were a directory, find pred, replace tail
      if (entry.d.type == LFS_TYPE_DIR) {
          int res = lfs_pred(lfs, dir.pair, &cwd);
          if (res < 0) {
              return res;
          }
  
          assert(res); // must have pred
          cwd.d.tail[0] = dir.d.tail[0];
          cwd.d.tail[1] = dir.d.tail[1];
  
          err = lfs_dir_commit(lfs, &cwd, NULL, 0);
          if (err) {
              return err;
          }
      }
  
      return 0;
  }
  
  int lfs_rename(lfs_t *lfs, const char *oldpath, const char *newpath) {
      // deorphan if we haven't yet, needed at most once after poweron
      if (!lfs->deorphaned) {
          int err = lfs_deorphan(lfs);
          if (err) {
              return err;
          }
      }
  
      // find old entry
      lfs_dir_t oldcwd;
      int err = lfs_dir_fetch(lfs, &oldcwd, lfs->root);
      if (err) {
          return err;
      }
  
      lfs_entry_t oldentry;
      err = lfs_dir_find(lfs, &oldcwd, &oldentry, &oldpath);
      if (err) {
          return err;
      }
  
      // allocate new entry
      lfs_dir_t newcwd;
      err = lfs_dir_fetch(lfs, &newcwd, lfs->root);
      if (err) {
          return err;
      }
  
      lfs_entry_t preventry;
      err = lfs_dir_find(lfs, &newcwd, &preventry, &newpath);
      if (err && (err != LFS_ERR_NOENT || strchr(newpath, '/') != NULL)) {
          return err;
      }
  
      bool prevexists = (err != LFS_ERR_NOENT);
      bool samepair = (lfs_paircmp(oldcwd.pair, newcwd.pair) == 0);
  
      // must have same type
      if (prevexists && preventry.d.type != oldentry.d.type) {
          return LFS_ERR_ISDIR;
      }
  
      lfs_dir_t dir;
      if (prevexists && preventry.d.type == LFS_TYPE_DIR) {
          // must be empty before removal, checking size
          // without masking top bit checks for any case where
          // dir is not empty
          err = lfs_dir_fetch(lfs, &dir, preventry.d.u.dir);
          if (err) {
              return err;
          } else if (dir.d.size != sizeof(dir.d)+4) {
              return LFS_ERR_NOTEMPTY;
          }
      }
  
      // mark as moving
      oldentry.d.type |= 0x80;
      err = lfs_dir_update(lfs, &oldcwd, &oldentry, NULL);
      if (err) {
          return err;
      }
  
      // update pair if newcwd == oldcwd
      if (samepair) {
          newcwd = oldcwd;
      }
  
      // move to new location
      lfs_entry_t newentry = preventry;
      newentry.d = oldentry.d;
      newentry.d.type &= ~0x80;
      newentry.d.nlen = strlen(newpath);
  
      if (prevexists) {
          err = lfs_dir_update(lfs, &newcwd, &newentry, newpath);
          if (err) {
              return err;
          }
      } else {
          err = lfs_dir_append(lfs, &newcwd, &newentry, newpath);
          if (err) {
              return err;
          }
      }
  
      // update pair if newcwd == oldcwd
      if (samepair) {
          oldcwd = newcwd;
      }
  
      // remove old entry
      err = lfs_dir_remove(lfs, &oldcwd, &oldentry);
      if (err) {
          return err;
      }
  
      // if we were a directory, find pred, replace tail
      if (prevexists && preventry.d.type == LFS_TYPE_DIR) {
          int res = lfs_pred(lfs, dir.pair, &newcwd);
          if (res < 0) {
              return res;
          }
  
          assert(res); // must have pred
          newcwd.d.tail[0] = dir.d.tail[0];
          newcwd.d.tail[1] = dir.d.tail[1];
  
          err = lfs_dir_commit(lfs, &newcwd, NULL, 0);
          if (err) {
              return err;
          }
      }
  
      return 0;
  }
  
  
  /// Filesystem operations ///
  static int lfs_init(lfs_t *lfs, const struct lfs_config *cfg) {
      lfs->cfg = cfg;
  
      // setup read cache
      lfs->rcache.block = 0xffffffff;
      if (lfs->cfg->read_buffer) {
          lfs->rcache.buffer = lfs->cfg->read_buffer;
      } else {
          lfs->rcache.buffer = malloc(lfs->cfg->read_size);
          if (!lfs->rcache.buffer) {
              return LFS_ERR_NOMEM;
          }
      }
  
      // setup program cache
      lfs->pcache.block = 0xffffffff;
      if (lfs->cfg->prog_buffer) {
          lfs->pcache.buffer = lfs->cfg->prog_buffer;
      } else {
          lfs->pcache.buffer = malloc(lfs->cfg->prog_size);
          if (!lfs->pcache.buffer) {
              return LFS_ERR_NOMEM;
          }
      }
  
      // setup lookahead, round down to nearest 32-bits
      assert(lfs->cfg->lookahead % 32 == 0);
      assert(lfs->cfg->lookahead > 0);
      if (lfs->cfg->lookahead_buffer) {
          lfs->free.buffer = lfs->cfg->lookahead_buffer;
      } else {
          lfs->free.buffer = malloc(lfs->cfg->lookahead/8);
          if (!lfs->free.buffer) {
              return LFS_ERR_NOMEM;
          }
      }
  
      // check that program and read sizes are multiples of the block size
      assert(lfs->cfg->prog_size % lfs->cfg->read_size == 0);
      assert(lfs->cfg->block_size % lfs->cfg->prog_size == 0);
  
      // check that the block size is large enough to fit ctz pointers
      assert(4*lfs_npw2(0xffffffff / (lfs->cfg->block_size-2*4))
              <= lfs->cfg->block_size);
  
      // setup default state
      lfs->root[0] = 0xffffffff;
      lfs->root[1] = 0xffffffff;
      lfs->files = NULL;
      lfs->dirs = NULL;
      lfs->deorphaned = false;
  
      return 0;
  }
  
  static int lfs_deinit(lfs_t *lfs) {
      // free allocated memory
      if (!lfs->cfg->read_buffer) {
          free(lfs->rcache.buffer);
      }
  
      if (!lfs->cfg->prog_buffer) {
          free(lfs->pcache.buffer);
      }
  
      if (!lfs->cfg->lookahead_buffer) {
          free(lfs->free.buffer);
      }
  
      return 0;
  }
  
  int lfs_format(lfs_t *lfs, const struct lfs_config *cfg) {
      int err = lfs_init(lfs, cfg);
      if (err) {
          return err;
      }
  
      // create free lookahead
      memset(lfs->free.buffer, 0, lfs->cfg->lookahead/8);
      lfs->free.begin = 0;
      lfs->free.size = lfs_min(lfs->cfg->lookahead, lfs->cfg->block_count);
      lfs->free.off = 0;
      lfs_alloc_ack(lfs);
  
      // create superblock dir
      lfs_dir_t superdir;
      err = lfs_dir_alloc(lfs, &superdir);
      if (err) {
          return err;
      }
  
      // write root directory
      lfs_dir_t root;
      err = lfs_dir_alloc(lfs, &root);
      if (err) {
          return err;
      }
  
      err = lfs_dir_commit(lfs, &root, NULL, 0);
      if (err) {
          return err;
      }
  
      lfs->root[0] = root.pair[0];
      lfs->root[1] = root.pair[1];
  
      // write superblocks
      lfs_superblock_t superblock = {
          .off = sizeof(superdir.d),
          .d.type = LFS_TYPE_SUPERBLOCK,
          .d.elen = sizeof(superblock.d) - sizeof(superblock.d.magic) - 4,
          .d.nlen = sizeof(superblock.d.magic),
          .d.version = LFS_DISK_VERSION,
          .d.magic = {"littlefs"},
          .d.block_size  = lfs->cfg->block_size,
          .d.block_count = lfs->cfg->block_count,
          .d.root = {lfs->root[0], lfs->root[1]},
      };
      superdir.d.tail[0] = root.pair[0];
      superdir.d.tail[1] = root.pair[1];
      superdir.d.size = sizeof(superdir.d) + sizeof(superblock.d) + 4;
  
      // write both pairs to be safe
      bool valid = false;
      for (int i = 0; i < 2; i++) {
          err = lfs_dir_commit(lfs, &superdir, (struct lfs_region[]){
                  {sizeof(superdir.d), sizeof(superblock.d),
                   &superblock.d, sizeof(superblock.d)}
              }, 1);
          if (err && err != LFS_ERR_CORRUPT) {
              return err;
          }
  
          valid = valid || !err;
      }
  
      if (!valid) {
          return LFS_ERR_CORRUPT;
      }
  
      // sanity check that fetch works
      err = lfs_dir_fetch(lfs, &superdir, (const lfs_block_t[2]){0, 1});
      if (err) {
          return err;
      }
  
      lfs_alloc_ack(lfs);
      return lfs_deinit(lfs);
  }
  
  int lfs_mount(lfs_t *lfs, const struct lfs_config *cfg) {
      int err = lfs_init(lfs, cfg);
      if (err) {
          return err;
      }
  
      // setup free lookahead
      lfs->free.begin = 0;
      lfs->free.size = 0;
      lfs->free.off = 0;
      lfs_alloc_ack(lfs);
  
      // load superblock
      lfs_dir_t dir;
      lfs_superblock_t superblock;
      err = lfs_dir_fetch(lfs, &dir, (const lfs_block_t[2]){0, 1});
      if (err && err != LFS_ERR_CORRUPT) {
          return err;
      }
  
      if (!err) {
          err = lfs_bd_read(lfs, dir.pair[0], sizeof(dir.d),
                  &superblock.d, sizeof(superblock.d));
          if (err) {
              return err;
          }
  
          lfs->root[0] = superblock.d.root[0];
          lfs->root[1] = superblock.d.root[1];
      }
  
      if (err || memcmp(superblock.d.magic, "littlefs", 8) != 0) {
          LFS_ERROR("Invalid superblock at %d %d", dir.pair[0], dir.pair[1]);
          return LFS_ERR_CORRUPT;
      }
  
      uint16_t major_version = (0xffff & (superblock.d.version >> 16));
      uint16_t minor_version = (0xffff & (superblock.d.version >>  0));
      if ((major_version != LFS_DISK_VERSION_MAJOR ||
           minor_version > LFS_DISK_VERSION_MINOR)) {
          LFS_ERROR("Invalid version %d.%d", major_version, minor_version);
          return LFS_ERR_INVAL;
      }
  
      return 0;
  }
  
  int lfs_unmount(lfs_t *lfs) {
      return lfs_deinit(lfs);
  }
  
  
  /// Littlefs specific operations ///
  int lfs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data) {
      if (lfs_pairisnull(lfs->root)) {
          return 0;
      }
  
      // iterate over metadata pairs
      lfs_dir_t dir;
      lfs_entry_t entry;
      lfs_block_t cwd[2] = {0, 1};
  
      while (true) {
          for (int i = 0; i < 2; i++) {
              int err = cb(data, cwd[i]);
              if (err) {
                  return err;
              }
          }
  
          int err = lfs_dir_fetch(lfs, &dir, cwd);
          if (err) {
              return err;
          }
  
          // iterate over contents
          while (dir.off + sizeof(entry.d) <= (0x7fffffff & dir.d.size)-4) {
              err = lfs_bd_read(lfs, dir.pair[0], dir.off,
                      &entry.d, sizeof(entry.d));
              if (err) {
                  return err;
              }
  
              dir.off += lfs_entry_size(&entry);
              if ((0x70 & entry.d.type) == (0x70 & LFS_TYPE_REG)) {
                  err = lfs_ctz_traverse(lfs, &lfs->rcache, NULL,
                          entry.d.u.file.head, entry.d.u.file.size, cb, data);
                  if (err) {
                      return err;
                  }
              }
          }
  
          cwd[0] = dir.d.tail[0];
          cwd[1] = dir.d.tail[1];
  
          if (lfs_pairisnull(cwd)) {
              break;
          }
      }
  
      // iterate over any open files
      for (lfs_file_t *f = lfs->files; f; f = f->next) {
          if (f->flags & LFS_F_DIRTY) {
              int err = lfs_ctz_traverse(lfs, &lfs->rcache, &f->cache,
                      f->head, f->size, cb, data);
              if (err) {
                  return err;
              }
          }
  
          if (f->flags & LFS_F_WRITING) {
              int err = lfs_ctz_traverse(lfs, &lfs->rcache, &f->cache,
                      f->block, f->pos, cb, data);
              if (err) {
                  return err;
              }
          }
      }
      
      return 0;
  }
  
  static int lfs_pred(lfs_t *lfs, const lfs_block_t dir[2], lfs_dir_t *pdir) {
      if (lfs_pairisnull(lfs->root)) {
          return 0;
      }
  
      // iterate over all directory directory entries
      int err = lfs_dir_fetch(lfs, pdir, (const lfs_block_t[2]){0, 1});
      if (err) {
          return err;
      }
  
      while (!lfs_pairisnull(pdir->d.tail)) {
          if (lfs_paircmp(pdir->d.tail, dir) == 0) {
              return true;
          }
  
          err = lfs_dir_fetch(lfs, pdir, pdir->d.tail);
          if (err) {
              return err;
          }
      }
  
      return false;
  }
  
  static int lfs_parent(lfs_t *lfs, const lfs_block_t dir[2],
          lfs_dir_t *parent, lfs_entry_t *entry) {
      if (lfs_pairisnull(lfs->root)) {
          return 0;
      }
      
      parent->d.tail[0] = 0;
      parent->d.tail[1] = 1;
  
      // iterate over all directory directory entries
      while (!lfs_pairisnull(parent->d.tail)) {
          int err = lfs_dir_fetch(lfs, parent, parent->d.tail);
          if (err) {
              return err;
          }
  
          while (true) {
              err = lfs_dir_next(lfs, parent, entry);
              if (err && err != LFS_ERR_NOENT) {
                  return err;
              }
  
              if (err == LFS_ERR_NOENT) {
                  break;
              }
  
              if (((0x70 & entry->d.type) == (0x70 & LFS_TYPE_DIR)) &&
                   lfs_paircmp(entry->d.u.dir, dir) == 0) {
                  return true;
              }
          }
      }
  
      return false;
  }
  
  static int lfs_moved(lfs_t *lfs, const void *e) {
      if (lfs_pairisnull(lfs->root)) {
          return 0;
      }
  
      // skip superblock
      lfs_dir_t cwd;
      int err = lfs_dir_fetch(lfs, &cwd, (const lfs_block_t[2]){0, 1});
      if (err) {
          return err;
      }
  
      // iterate over all directory directory entries
      lfs_entry_t entry;
      while (!lfs_pairisnull(cwd.d.tail)) {
          err = lfs_dir_fetch(lfs, &cwd, cwd.d.tail);
          if (err) {
              return err;
          }
  
          while (true) {
              err = lfs_dir_next(lfs, &cwd, &entry);
              if (err && err != LFS_ERR_NOENT) {
                  return err;
              }
  
              if (err == LFS_ERR_NOENT) {
                  break;
              }
  
              if (!(0x80 & entry.d.type) && 
                   memcmp(&entry.d.u, e, sizeof(entry.d.u)) == 0) {
                  return true;
              }
          }
      }
  
      return false;
  }
  
  static int lfs_relocate(lfs_t *lfs,
          const lfs_block_t oldpair[2], const lfs_block_t newpair[2]) {
      // find parent
      lfs_dir_t parent;
      lfs_entry_t entry;
      int res = lfs_parent(lfs, oldpair, &parent, &entry);
      if (res < 0) {
          return res;
      }
  
      if (res) {
          // update disk, this creates a desync
          entry.d.u.dir[0] = newpair[0];
          entry.d.u.dir[1] = newpair[1];
  
          int err = lfs_dir_update(lfs, &parent, &entry, NULL);
          if (err) {
              return err;
          }
  
          // update internal root
          if (lfs_paircmp(oldpair, lfs->root) == 0) {
              LFS_DEBUG("Relocating root %d %d", newpair[0], newpair[1]);
              lfs->root[0] = newpair[0];
              lfs->root[1] = newpair[1];
          }
  
          // clean up bad block, which should now be a desync
          return lfs_deorphan(lfs);
      }
  
      // find pred
      res = lfs_pred(lfs, oldpair, &parent);
      if (res < 0) {
          return res;
      }
  
      if (res) {
          // just replace bad pair, no desync can occur
          parent.d.tail[0] = newpair[0];
          parent.d.tail[1] = newpair[1];
  
          return lfs_dir_commit(lfs, &parent, NULL, 0);
      }
  
      // couldn't find dir, must be new
      return 0;
  }
  
  int lfs_deorphan(lfs_t *lfs) {
      lfs->deorphaned = true;
  
      if (lfs_pairisnull(lfs->root)) {
          return 0;
      }
  
      lfs_dir_t pdir = {.d.size = 0x80000000};
      lfs_dir_t cwd = {.d.tail[0] = 0, .d.tail[1] = 1};
  
      // iterate over all directory directory entries
      while (!lfs_pairisnull(cwd.d.tail)) {
          int err = lfs_dir_fetch(lfs, &cwd, cwd.d.tail);
          if (err) {
              return err;
          }
  
          // check head blocks for orphans
          if (!(0x80000000 & pdir.d.size)) {
              // check if we have a parent
              lfs_dir_t parent;
              lfs_entry_t entry;
              int res = lfs_parent(lfs, pdir.d.tail, &parent, &entry);
              if (res < 0) {
                  return res;
              }
  
              if (!res) {
                  // we are an orphan
                  LFS_DEBUG("Found orphan %d %d",
                          pdir.d.tail[0], pdir.d.tail[1]);
  
                  pdir.d.tail[0] = cwd.d.tail[0];
                  pdir.d.tail[1] = cwd.d.tail[1];
  
                  err = lfs_dir_commit(lfs, &pdir, NULL, 0);
                  if (err) {
                      return err;
                  }
  
                  break;
              }
  
              if (!lfs_pairsync(entry.d.u.dir, pdir.d.tail)) {
                  // we have desynced
                  LFS_DEBUG("Found desync %d %d",
                          entry.d.u.dir[0], entry.d.u.dir[1]);
  
                  pdir.d.tail[0] = entry.d.u.dir[0];
                  pdir.d.tail[1] = entry.d.u.dir[1];
  
                  err = lfs_dir_commit(lfs, &pdir, NULL, 0);
                  if (err) {
                      return err;
                  }
  
                  break;
              }
          }
  
          // check entries for moves
          lfs_entry_t entry;
          while (true) {
              err = lfs_dir_next(lfs, &cwd, &entry);
              if (err && err != LFS_ERR_NOENT) {
                  return err;
              }
  
              if (err == LFS_ERR_NOENT) {
                  break;
              }
  
              // found moved entry
              if (entry.d.type & 0x80) {
                  int moved = lfs_moved(lfs, &entry.d.u);
                  if (moved < 0) {
                      return moved;
                  }
  
                  if (moved) {
                      LFS_DEBUG("Found move %d %d",
                              entry.d.u.dir[0], entry.d.u.dir[1]);
                      err = lfs_dir_remove(lfs, &cwd, &entry);
                      if (err) {
                          return err;
                      }
                  } else {
                      LFS_DEBUG("Found partial move %d %d",
                              entry.d.u.dir[0], entry.d.u.dir[1]);
                      entry.d.type &= ~0x80;
                      err = lfs_dir_update(lfs, &cwd, &entry, NULL);
                      if (err) {
                          return err;
                      }
                  }
              }
          }
  
          memcpy(&pdir, &cwd, sizeof(pdir));
      }
  
      return 0;
  }
  
  