support copying files in volume

Signed-off-by: fahed dorgaa <fahed.dorgaa@gmail.com>

go.mod

@@ -7,6 +7,7 @@ require (
 	github.com/containerd/cgroups v0.0.0-20210114181951-8a68de567b68
 	github.com/containerd/console v1.0.2
 	github.com/containerd/containerd v1.5.0-rc.1
+	github.com/containerd/continuity v0.0.0-20210208174643-50096c924a4e
 	github.com/containerd/go-cni v1.0.1
 	github.com/containerd/imgcrypt v1.1.1
 	github.com/containerd/stargz-snapshotter v0.5.0

run.go

@@ -315,6 +315,7 @@ func runAction(clicontext *cli.Context) error {
 	if ensuredImage != nil {
 		imageVolumes = ensuredImage.ImageConfig.Volumes
 	}
+
 	mountOpts, anonVolumes, err := generateMountOpts(clicontext, imageVolumes)
 	if err != nil {
 		return err

run_mount.go

@@ -17,12 +17,20 @@
 package main
 
 import (
+	"io/ioutil"
+	"os"
 	"path/filepath"
+	"strings"
 
+	"github.com/containerd/containerd"
+	"github.com/containerd/containerd/errdefs"
+	"github.com/containerd/containerd/mount"
 	"github.com/containerd/containerd/oci"
+	"github.com/containerd/continuity/fs"
 	"github.com/containerd/nerdctl/pkg/idgen"
 	"github.com/containerd/nerdctl/pkg/mountutil"
 	"github.com/containerd/nerdctl/pkg/strutil"
+	"github.com/opencontainers/image-spec/identity"
 	"github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
@@ -69,12 +77,59 @@ func generateMountOpts(clicontext *cli.Context, imageVolumes map[string]struct{}
 			continue
 		}
 		anonVolName := idgen.GenerateID()
+
 		logrus.Debugf("creating anonymous volume %q, for \"VOLUME %s\"",
 			anonVolName, imgVolRaw)
 		anonVol, err := volStore.Create(anonVolName)
 		if err != nil {
 			return nil, nil, err
 		}
+
+		client, ctx, cancel, err := newClient(clicontext)
+		if err != nil {
+			return nil, nil, err
+		}
+		defer cancel()
+
+		img, err := client.ImageService().Get(ctx, clicontext.Args().First())
+		if err != nil {
+			return nil, nil, err
+		}
+
+		i := containerd.NewImage(client, img)
+
+		if err := i.Unpack(ctx, clicontext.String("snapshotter")); err != nil {
+			return nil, nil, errors.Wrap(err, "error unpacking image")
+		}
+
+		diffIDs, err := i.RootFS(ctx)
+		if err != nil {
+			return nil, nil, err
+		}
+		chainID := identity.ChainID(diffIDs).String()
+
+		s := client.SnapshotService(clicontext.String("snapshotter"))
+
+		tempDir, err := ioutil.TempDir(os.Getenv("GOTMPDIR"), "initialC")
+		if err != nil {
+			return nil, nil, err
+		}
+		defer os.RemoveAll(tempDir)
+
+		var mounts []mount.Mount
+		mounts, err = s.View(ctx, tempDir, chainID)
+
+		if err := mount.All(mounts, tempDir); err != nil {
+			if err := s.Remove(ctx, tempDir); err != nil && !errdefs.IsNotFound(err) {
+				return nil, nil, err
+			}
+			return nil, nil, err
+		}
+		target := strings.Join([]string{tempDir, imgVol}, "")
+
+		//copying up initial contents of the mount point directory
+		copyExistingContents(target, anonVol.Mountpoint)
+
 		m := []specs.Mount{
 			{
 				Type:        "none",
@@ -83,9 +138,23 @@ func generateMountOpts(clicontext *cli.Context, imageVolumes map[string]struct{}
 				Options:     []string{"rbind"},
 			},
 		}
+
 		opts = append(opts, oci.WithMounts(m))
 		anonVolumes = append(anonVolumes, anonVolName)
 	}
 
 	return opts, anonVolumes, nil
 }
+
+// copyExistingContents copies from the source to the destination and
+// ensures the ownership is appropriately set.
+func copyExistingContents(source, destination string) error {
+	dstList, err := ioutil.ReadDir(destination)
+	if err != nil {
+		return err
+	}
+	if len(dstList) != 0 {
+		return errors.Errorf("volume at %q is not initially empty", destination)
+	}
+	return fs.CopyDir(destination, source)
+}

run_mount_test.go

@@ -98,3 +98,24 @@ VOLUME /foo
 	base.Cmd("run", "--rm", "-v", "/foo", testutil.AlpineImage,
 		"mountpoint", "-q", "/foo").AssertOK()
 }
+
+func TestCopyingUpInitialContentsOnAnonymousVolume(t *testing.T) {
+	t.Parallel()
+	testutil.RequiresBuild(t)
+	base := testutil.NewBase(t)
+	const imageName = "nerdctl-test-copying-initial-content-on-anonvolume"
+	defer base.Cmd("rmi", imageName).Run()
+
+	dockerfile := fmt.Sprintf(`FROM %s
+RUN mkdir -p /mnt && echo hi > /mnt/initial_file
+VOLUME /mnt
+CMD ["cat", "/mnt/initial_file"]
+        `, testutil.AlpineImage)
+
+	buildCtx, err := createBuildContext(dockerfile)
+	assert.NilError(t, err)
+	defer os.RemoveAll(buildCtx)
+
+	base.Cmd("build", "-t", imageName, buildCtx).AssertOK()
+	base.Cmd("run", "--rm", imageName).AssertOK()
+}