volume: Add support for overlay on named volumes

Following PR allows containers to create and mount overlays on top of
named volumes instead of mounting actual volumes via already documented `:O`.

Signed-off-by: Aditya Rajan <arajan@redhat.com>

libpod/container_internal_linux.go

@@ -369,13 +369,46 @@ func (c *Container) generateSpec(ctx context.Context) (*spec.Spec, error) {
 		if err != nil {
 			return nil, err
 		}
-		volMount := spec.Mount{
+
-			Type:        "bind",
+		overlayFlag := false
-			Source:      mountPoint,
+		for _, o := range namedVol.Options {
-			Destination: namedVol.Dest,
+			if o == "O" {
-			Options:     namedVol.Options,
+				overlayFlag = true
+			}
+		}
+
+		if overlayFlag {
+			contentDir, err := overlay.TempDir(c.config.StaticDir, c.RootUID(), c.RootGID())
+			if err != nil {
+				return nil, err
+			}
+			overlayMount, err := overlay.Mount(contentDir, mountPoint, namedVol.Dest, c.RootUID(), c.RootGID(), c.runtime.store.GraphOptions())
+			if err != nil {
+				return nil, errors.Wrapf(err, "mounting overlay failed %q", mountPoint)
+			}
+
+			for _, o := range namedVol.Options {
+				switch o {
+				case "U":
+					if err := chown.ChangeHostPathOwnership(mountPoint, true, int(hostUID), int(hostGID)); err != nil {
+						return nil, err
+					}
+
+					if err := chown.ChangeHostPathOwnership(contentDir, true, int(hostUID), int(hostGID)); err != nil {
+						return nil, err
+					}
+				}
+			}
+			g.AddMount(overlayMount)
+		} else {
+			volMount := spec.Mount{
+				Type:        "bind",
+				Source:      mountPoint,
+				Destination: namedVol.Dest,
+				Options:     namedVol.Options,
+			}
+			g.AddMount(volMount)
 		}
-		g.AddMount(volMount)
 	}
 
 	// Check if the spec file mounts contain the options z, Z or U.

test/e2e/run_volume_test.go

@@ -242,6 +242,39 @@ var _ = Describe("Podman run with volumes", func() {
 		Expect(session).Should(Exit(0))
 	})
 
+	It("podman support overlay on named volume", func() {
+		SkipIfRemote("Overlay volumes only work locally")
+		if os.Getenv("container") != "" {
+			Skip("Overlay mounts not supported when running in a container")
+		}
+		if rootless.IsRootless() {
+			if _, err := exec.LookPath("fuse-overlayfs"); err != nil {
+				Skip("Fuse-Overlayfs required for rootless overlay mount test")
+			}
+		}
+		session := podmanTest.Podman([]string{"volume", "create", "myvolume"})
+		session.WaitWithDefaultTimeout()
+		volName := session.OutputToString()
+		Expect(session).Should(Exit(0))
+
+		// create file on actual volume
+		session = podmanTest.Podman([]string{"run", "--volume", volName + ":/data", ALPINE, "sh", "-c", "echo hello >> " + "/data/test"})
+		session.WaitWithDefaultTimeout()
+		Expect(session).Should(Exit(0))
+
+		// create file on overlayed volume
+		session = podmanTest.Podman([]string{"run", "--volume", volName + ":/data:O", ALPINE, "sh", "-c", "echo hello >> " + "/data/overlayed"})
+		session.WaitWithDefaultTimeout()
+		Expect(session).Should(Exit(0))
+
+		// volume should contain only `test` not `overlayed`
+		session = podmanTest.Podman([]string{"run", "--volume", volName + ":/data", ALPINE, "sh", "-c", "ls /data"})
+		session.WaitWithDefaultTimeout()
+		Expect(session.OutputToString()).To(Not(ContainSubstring("overlayed")))
+		Expect(session.OutputToString()).To(ContainSubstring("test"))
+
+	})
+
 	It("podman run with noexec can't exec", func() {
 		session := podmanTest.Podman([]string{"run", "--rm", "-v", "/bin:/hostbin:noexec", ALPINE, "/hostbin/ls", "/"})
 		session.WaitWithDefaultTimeout()