Implement overlay fs snapshot driver

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

snapshot/overlayfs_test.go

@@ -0,0 +1,180 @@
+package snapshot
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"syscall"
+	"testing"
+
+	"github.com/docker/containerd"
+)
+
+func TestOverlayfs(t *testing.T) {
+	root, err := ioutil.TempDir("", "overlay")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(root)
+	o, err := NewOverlayfs(root)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	mounts, err := o.Prepare("/tmp/test", "")
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	if len(mounts) != 1 {
+		t.Errorf("should only have 1 mount but received %d", len(mounts))
+	}
+	m := mounts[0]
+	if m.Type != "bind" {
+		t.Errorf("mount type should be bind but received %q", m.Type)
+	}
+	expected := filepath.Join(root, "active", hash("/tmp/test"), "fs")
+	if m.Source != expected {
+		t.Errorf("expected source %q but received %q", expected, m.Source)
+	}
+	if m.Options[0] != "rw" {
+		t.Errorf("expected mount option rw but received %q", m.Options[0])
+	}
+	if m.Options[1] != "rbind" {
+		t.Errorf("expected mount option rbind but received %q", m.Options[1])
+	}
+}
+
+func TestOverlayfsCommit(t *testing.T) {
+	root, err := ioutil.TempDir("", "overlay")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(root)
+	o, err := NewOverlayfs(root)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	key := "/tmp/test"
+	mounts, err := o.Prepare(key, "")
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	m := mounts[0]
+	if err := ioutil.WriteFile(filepath.Join(m.Source, "foo"), []byte("hi"), 0660); err != nil {
+		t.Error(err)
+		return
+	}
+	if err := o.Commit(key, "base"); err != nil {
+		t.Error(err)
+		return
+	}
+}
+
+func TestOverlayfsOverlayMount(t *testing.T) {
+	root, err := ioutil.TempDir("", "overlay")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(root)
+	o, err := NewOverlayfs(root)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	key := "/tmp/test"
+	mounts, err := o.Prepare(key, "")
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	if err := o.Commit(key, "base"); err != nil {
+		t.Error(err)
+		return
+	}
+	if mounts, err = o.Prepare("/tmp/layer2", "base"); err != nil {
+		t.Error(err)
+		return
+	}
+	if len(mounts) != 1 {
+		t.Errorf("should only have 1 mount but received %d", len(mounts))
+	}
+	m := mounts[0]
+	if m.Type != "overlay" {
+		t.Errorf("mount type should be overlay but received %q", m.Type)
+	}
+	if m.Source != "overlay" {
+		t.Errorf("expected source %q but received %q", "overlay", m.Source)
+	}
+	var (
+		hash  = hash("/tmp/layer2")
+		work  = "workdir=" + filepath.Join(root, "active", hash, "work")
+		upper = "upperdir=" + filepath.Join(root, "active", hash, "fs")
+		lower = "lowerdir=" + filepath.Join(root, "snapshots", "base", "fs")
+	)
+	for i, v := range []string{
+		work,
+		upper,
+		lower,
+	} {
+		if m.Options[i] != v {
+			t.Errorf("expected %q but received %q", v, m.Options[i])
+		}
+	}
+}
+
+func TestOverlayfsOverlayRead(t *testing.T) {
+	if os.Getuid() != 0 {
+		t.Skip("not running as root")
+	}
+	root, err := ioutil.TempDir("", "overlay")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(root)
+	o, err := NewOverlayfs(root)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	key := "/tmp/test"
+	mounts, err := o.Prepare(key, "")
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	m := mounts[0]
+	if err := ioutil.WriteFile(filepath.Join(m.Source, "foo"), []byte("hi"), 0660); err != nil {
+		t.Error(err)
+		return
+	}
+	if err := o.Commit(key, "base"); err != nil {
+		t.Error(err)
+		return
+	}
+	if mounts, err = o.Prepare("/tmp/layer2", "base"); err != nil {
+		t.Error(err)
+		return
+	}
+	dest := filepath.Join(root, "dest")
+	if err := os.Mkdir(dest, 0700); err != nil {
+		t.Error(err)
+		return
+	}
+	if err := containerd.MountFS(mounts, dest); err != nil {
+		t.Error(err)
+		return
+	}
+	defer syscall.Unmount(dest, 0)
+	data, err := ioutil.ReadFile(filepath.Join(dest, "foo"))
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	if e := string(data); e != "hi" {
+		t.Errorf("expected file contents hi but got %q", e)
+		return
+	}
+}