Switch from syscall.Getdents to unix.Getdents

On mips64le, syscall.Getdents() and struct syscall.Dirent do
not fit together, causing our parseDirents() implementation to
return garbage ( see rfjakob/gocryptfs#200
and golang/go#23624 ).

Switch to unix.Getdents which does not have this problem -
the next Go release with the syscall package fixes is too
far away, and will take time to trickle into distros.

This issue has been reported by Debian maintainer
Felix Lechner.

fuse/test/loopback_linux_test.go

@@ -11,6 +11,8 @@ import (
 	"testing"
 	"time"
 
+	"golang.org/x/sys/unix"
+
 	"github.com/hanwen/go-fuse/fuse"
 )
 
@@ -143,7 +145,7 @@ func TestFallocate(t *testing.T) {
 	}
 }
 
-// Check that "." and ".." exists. syscall.Getdents is linux specific.
+// Check that "." and ".." exists. unix.Getdents is linux specific.
 func TestSpecialEntries(t *testing.T) {
 	tc := NewTestCase(t)
 	defer tc.Cleanup()
@@ -154,7 +156,7 @@ func TestSpecialEntries(t *testing.T) {
 	}
 	defer d.Close()
 	buf := make([]byte, 100)
-	n, err := syscall.Getdents(int(d.Fd()), buf)
+	n, err := unix.Getdents(int(d.Fd()), buf)
 	if n == 0 {
 		t.Errorf("directory is empty, entries '.' and '..' are missing")
 	}
@@ -180,7 +182,7 @@ func TestReaddirInodes(t *testing.T) {
 	buf := make([]byte, 100)
 	// readdir(3) use getdents64(2) internally which returns linux_dirent64
 	// structures. We don't have readdir(3) so we call getdents64(2) directly.
-	n, err := syscall.Getdents(int(d.Fd()), buf)
+	n, err := unix.Getdents(int(d.Fd()), buf)
 	if n == 0 {
 		t.Error("empty directory - we need at least one file")
 	}

fuse/test/xfs_test.go

@@ -13,6 +13,8 @@ import (
 	"syscall"
 	"testing"
 	"unsafe"
+
+	"golang.org/x/sys/unix"
 )
 
 func clen(n []byte) int {
@@ -34,7 +36,7 @@ type CDirent struct {
 func parseDirents(buf []byte) []CDirent {
 	var result []CDirent
 	for len(buf) > 0 {
-		de := *(*syscall.Dirent)(unsafe.Pointer(&buf[0]))
+		de := *(*unix.Dirent)(unsafe.Pointer(&buf[0]))
 		buf = buf[de.Reclen:]
 		bytes := (*[10000]byte)(unsafe.Pointer(&de.Name[0]))
 		var name = string(bytes[0:clen(bytes[:])])