posixtest: add DirSeek test, Go port of xfstests generic/257

Regression test for https://github.com/hanwen/go-fuse/issues/344
"[v2 API] xfstests generic/257 fails (getdents seek trouble)"

Change-Id: Icefab07f6762f8e56de525713facf992797d4435

posixtest/test.go

@@ -40,6 +40,7 @@ var All = map[string]func(*testing.T, string){
 	"DirectIO":                   DirectIO,
 	"OpenAt":                     OpenAt,
 	"Fallocate":                  Fallocate,
+	"DirSeek":                    DirSeek,
 }
 
 func DirectIO(t *testing.T, mnt string) {

posixtest/xfstests.go

+package posixtest
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"syscall"
+	"testing"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+// DirSeek tests that seeking on a directory works for
+// https://github.com/hanwen/go-fuse/issues/344 .
+//
+// Go port of xfstests generic/257.
+//
+// Hint:
+// $ go test ./fs -run TestPosix/DirSeek -v
+func DirSeek(t *testing.T, mnt string) {
+	// From bash script xfstests/tests/generic/257
+	ttt := mnt + "/ttt"
+	err := os.Mkdir(ttt, 0700)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for i := 1; i <= 168; i++ {
+		path := fmt.Sprintf("%s/%d", ttt, i)
+		err = ioutil.WriteFile(path, nil, 0600)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	// From C app xfstests/src/t_dir_offset2.c
+	const bufSize = 4096
+	const historyLen = 1024
+	offHistory := make([]int64, historyLen)
+	inoHistory := make([]uint64, historyLen)
+	buf := make([]byte, bufSize)
+	fd, err := syscall.Open(ttt, syscall.O_RDONLY|syscall.O_DIRECTORY, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer syscall.Close(fd)
+
+	total := 0
+	for {
+		n, err := unix.Getdents(fd, buf)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if n == 0 {
+			break
+		}
+		for bpos := 0; bpos < n; total++ {
+			d := (*unix.Dirent)(unsafe.Pointer(&buf[bpos]))
+			if total > historyLen {
+				t.Fatal("too many files")
+			}
+			for i := 0; i < total; i++ {
+				if offHistory[i] == d.Off {
+					t.Errorf("entries %d and %d gave duplicate d.Off %d",
+						i, total, d.Off)
+				}
+			}
+			offHistory[total] = d.Off
+			inoHistory[total] = d.Ino
+			bpos += int(d.Reclen)
+		}
+	}
+
+	// check if seek works correctly
+	d := (*unix.Dirent)(unsafe.Pointer(&buf[0]))
+	for i := total - 1; i >= 0; i-- {
+		var seekTo int64
+		if i > 0 {
+			seekTo = offHistory[i-1]
+		}
+		_, err = unix.Seek(fd, seekTo, os.SEEK_SET)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		n, err := unix.Getdents(fd, buf)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if n == 0 {
+			t.Errorf("getdents returned 0 on entry %d", i)
+			continue
+		}
+
+		if d.Ino != inoHistory[i] {
+			t.Errorf("entry %d has inode %d, expected %d",
+				i, d.Ino, inoHistory[i])
+		}
+	}
+}