func GetDirUsage()

in fs/fs.go [604:665]
46 lines of code
11 McCabe index (conditional complexity)

func GetDirUsage(dir string) (UsageInfo, error) {
	var usage UsageInfo

	if dir == "" {
		return usage, fmt.Errorf("invalid directory")
	}

	rootInfo, err := os.Stat(dir)
	if err != nil {
		return usage, fmt.Errorf("could not stat %q to get inode usage: %v", dir, err)
	}

	rootStat, ok := rootInfo.Sys().(*syscall.Stat_t)
	if !ok {
		return usage, fmt.Errorf("unsuported fileinfo for getting inode usage of %q", dir)
	}

	rootDevID := rootStat.Dev

	// dedupedInode stores inodes that could be duplicates (nlink > 1)
	dedupedInodes := make(map[uint64]struct{})

	err = filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
		if os.IsNotExist(err) {
			// expected if files appear/vanish
			return nil
		}
		if err != nil {
			return fmt.Errorf("unable to count inodes for part of dir %s: %s", dir, err)
		}

		// according to the docs, Sys can be nil
		if info.Sys() == nil {
			return fmt.Errorf("fileinfo Sys is nil")
		}

		s, ok := info.Sys().(*syscall.Stat_t)
		if !ok {
			return fmt.Errorf("unsupported fileinfo; could not convert to stat_t")
		}

		if s.Dev != rootDevID {
			// don't descend into directories on other devices
			return filepath.SkipDir
		}
		if s.Nlink > 1 {
			if _, ok := dedupedInodes[s.Ino]; !ok {
				// Dedupe things that could be hardlinks
				dedupedInodes[s.Ino] = struct{}{}

				usage.Bytes += uint64(s.Blocks) * statBlockSize
				usage.Inodes++
			}
		} else {
			usage.Bytes += uint64(s.Blocks) * statBlockSize
			usage.Inodes++
		}
		return nil
	})

	return usage, err
}