Initial DDC release

internal/diskspace/diskspace.go

@@ -0,0 +1,38 @@
+package diskspace
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"syscall"
+)
+
+var ErrInsufficientSpace = errors.New("not enough free disk space")
+
+func Available(path string) (int64, error) {
+	var stats syscall.Statfs_t
+	if err := syscall.Statfs(path, &stats); err != nil {
+		return 0, err
+	}
+	available := stats.Bavail * uint64(stats.Bsize)
+	if available > math.MaxInt64 {
+		return math.MaxInt64, nil
+	}
+	return int64(available), nil
+}
+
+func EnsureFree(path string, requiredBytes, reservedBytes int64) error {
+	available, err := Available(path)
+	if err != nil {
+		return err
+	}
+	if available-reservedBytes < requiredBytes {
+		return fmt.Errorf("%w: %.1f GiB needed, %.1f GiB usable after keeping %.1f GiB free",
+			ErrInsufficientSpace, toGiB(requiredBytes), toGiB(available-reservedBytes), toGiB(reservedBytes))
+	}
+	return nil
+}
+
+func toGiB(bytes int64) float64 {
+	return float64(bytes) / float64(1<<30)
+}