import github.com/moby/moby/pkg/fsutils (v17.05.0-ce) as fs/fsutils

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

fs/fsutils/fsutils_linux.go

@@ -0,0 +1,87 @@
+// +build linux
+
+package fsutils
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+func locateDummyIfEmpty(path string) (string, error) {
+	children, err := ioutil.ReadDir(path)
+	if err != nil {
+		return "", err
+	}
+	if len(children) != 0 {
+		return "", nil
+	}
+	dummyFile, err := ioutil.TempFile(path, "fsutils-dummy")
+	if err != nil {
+		return "", err
+	}
+	name := dummyFile.Name()
+	err = dummyFile.Close()
+	return name, err
+}
+
+// SupportsDType returns whether the filesystem mounted on path supports d_type
+func SupportsDType(path string) (bool, error) {
+	// locate dummy so that we have at least one dirent
+	dummy, err := locateDummyIfEmpty(path)
+	if err != nil {
+		return false, err
+	}
+	if dummy != "" {
+		defer os.Remove(dummy)
+	}
+
+	visited := 0
+	supportsDType := true
+	fn := func(ent *syscall.Dirent) bool {
+		visited++
+		if ent.Type == syscall.DT_UNKNOWN {
+			supportsDType = false
+			// stop iteration
+			return true
+		}
+		// continue iteration
+		return false
+	}
+	if err = iterateReadDir(path, fn); err != nil {
+		return false, err
+	}
+	if visited == 0 {
+		return false, fmt.Errorf("did not hit any dirent during iteration %s", path)
+	}
+	return supportsDType, nil
+}
+
+func iterateReadDir(path string, fn func(*syscall.Dirent) bool) error {
+	d, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	defer d.Close()
+	fd := int(d.Fd())
+	buf := make([]byte, 4096)
+	for {
+		nbytes, err := syscall.ReadDirent(fd, buf)
+		if err != nil {
+			return err
+		}
+		if nbytes == 0 {
+			break
+		}
+		for off := 0; off < nbytes; {
+			ent := (*syscall.Dirent)(unsafe.Pointer(&buf[off]))
+			if stop := fn(ent); stop {
+				return nil
+			}
+			off += int(ent.Reclen)
+		}
+	}
+	return nil
+}