Add lfs_fs_grow to enable limited resizing of the filesystem

[geky]

Originally proposed by @kaetemi, this API allows you to change the size of the filesystem on disk to take advantage of additional space if it becomes available:

  cfg.block_count = 1024;

  int err = lfs_mount(lfs, cfg);
  if (err) {
      return err;
  }

  struct lfs_fsstat fsstat;
  err = lfs_fs_stat(lfs, &fsstat);
  if (err) {
      return err;
  }
  printf("block_count: %d\n", fsstat.block_count); // prints 1024

  err = lfs_fs_grow(lfs, 2048);
  if (err) {
      return err;
  }

  struct lfs_fsstat fsstat;
  err = lfs_fs_stat(lfs, &fsstat);
  if (err) {
      return err;
  }
  printf("block_count: %d\n", fsstat.block_count); // prints 2048

If you want to automatically resize littlefs to the full disk size every mount, this can be done by using these two calls as your "mount" operation:

  lfs_size_t required_block_count = DISK_SIZE / BLOCK_SIZE;

  // unknown block_count
  cfg.block_count = 0;

  // mount and resize if disk has grown
  int err = lfs_mount(lfs, cfg);
  if (err) {
      return err;
  }

  err = lfs_fs_grow(lfs, required_block_count);
  if (err) {
      return err;
  }

---

See https://github.com/littlefs-project/littlefs/pull/702, https://github.com/littlefs-project/littlefs/issues/279, and https://github.com/littlefs-project/littlefs/pull/753 for related discussions.

This depends on https://github.com/littlefs-project/littlefs/pull/866, which makes block_size optional

[geky-bot]

Tests passed ✓, Code: 16810 B (+0.8%), Stack: 1432 B (+0.0%), Structs: 800 B (+1.5%)

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