rootfs: Add support for rootfs-overlay and bump to buildah v1.22.1-0.202108

Allows users to specify a readonly rootfs with :O, in exchange podman will create a writable overlay.

bump builah to v1.22.1-0.20210823173221-da2b428c56ce

[NO TESTS NEEDED]

Signed-off-by: flouthoc <flouthoc.git@gmail.com>

3 files changed, 42 insertions, 1 deletions

diff --git a/libpod/container_config.go b/libpod/container_config.go
index b80b23c25..a2c989a1a 100644
--- a/libpod/container_config.go
+++ b/libpod/container_config.go
@@ -107,6 +107,8 @@ type ContainerRootFSConfig struct {
 	// as the container's root.
 	// Conflicts with RootfsImageID.
 	Rootfs string `json:"rootfs,omitempty"`
+	// RootfsOverlay tells if rootfs has to be mounted as an overlay
+	RootfsOverlay bool `json:"rootfs_overlay,omitempty"`
 	// ShmDir is the path to be mounted on /dev/shm in container.
 	// If not set manually at creation time, Libpod will create a tmpfs
 	// with the size specified in ShmSize and populate this with the path of
diff --git a/libpod/container_internal.go b/libpod/container_internal.go
index 4d1a25541..63683a8b8 100644
--- a/libpod/container_internal.go
+++ b/libpod/container_internal.go
@@ -15,6 +15,7 @@ import (
 
 	metadata "github.com/checkpoint-restore/checkpointctl/lib"
 	"github.com/containers/buildah/copier"
+	"github.com/containers/buildah/pkg/overlay"
 	butil "github.com/containers/buildah/util"
 	"github.com/containers/podman/v3/libpod/define"
 	"github.com/containers/podman/v3/libpod/events"
@@ -1541,6 +1542,32 @@ func (c *Container) mountStorage() (_ string, deferredErr error) {
 	// We need to mount the container before volumes - to ensure the copyup
 	// works properly.
 	mountPoint := c.config.Rootfs
+	// Check if overlay has to be created on top of Rootfs
+	if c.config.RootfsOverlay {
+		overlayDest := c.runtime.store.GraphRoot()
+		contentDir, err := overlay.GenerateStructure(c.runtime.store.GraphRoot(), c.ID(), "rootfs", c.RootUID(), c.RootGID())
+		if err != nil {
+			return "", errors.Wrapf(err, "rootfs-overlay: failed to create TempDir in the %s directory", overlayDest)
+		}
+		overlayMount, err := overlay.Mount(contentDir, c.config.Rootfs, overlayDest, c.RootUID(), c.RootGID(), c.runtime.store.GraphOptions())
+		if err != nil {
+			return "", errors.Wrapf(err, "rootfs-overlay: creating overlay failed %q", c.config.Rootfs)
+		}
+
+		// Seems fuse-overlayfs is not present
+		// fallback to native overlay
+		if overlayMount.Type == "overlay" {
+			overlayMount.Options = append(overlayMount.Options, "nodev")
+			mountOpts := label.FormatMountLabel(strings.Join(overlayMount.Options, ","), c.MountLabel())
+			err = mount.Mount("overlay", overlayMount.Source, overlayMount.Type, mountOpts)
+			if err != nil {
+				return "", errors.Wrapf(err, "rootfs-overlay: creating overlay failed %q from native overlay", c.config.Rootfs)
+			}
+		}
+
+		mountPoint = overlayMount.Source
+	}
+
 	if mountPoint == "" {
 		mountPoint, err = c.mount()
 		if err != nil {
@@ -1714,6 +1741,17 @@ func (c *Container) cleanupStorage() error {
 
 	var cleanupErr error
 
+	// umount rootfs overlay if it was created
+	if c.config.RootfsOverlay {
+		overlayBasePath := c.runtime.store.GraphRoot()
+		overlayBasePath = filepath.Join(overlayBasePath, "rootfs")
+		if err := overlay.Unmount(overlayBasePath); err != nil {
+			// If the container can't remove content report the error
+			logrus.Errorf("Failed to cleanup overlay mounts for %s: %v", c.ID(), err)
+			cleanupErr = err
+		}
+	}
+
 	for _, containerMount := range c.config.Mounts {
 		if err := c.unmountSHM(containerMount); err != nil {
 			if cleanupErr != nil {
diff --git a/libpod/options.go b/libpod/options.go
index 4cbd2b5e2..7b0c6641a 100644
--- a/libpod/options.go
+++ b/libpod/options.go
@@ -1337,7 +1337,7 @@ func WithCommand(command []string) CtrCreateOption {
 
 // WithRootFS sets the rootfs for the container.
 // This creates a container from a directory on disk and not an image.
-func WithRootFS(rootfs string) CtrCreateOption {
+func WithRootFS(rootfs string, overlay bool) CtrCreateOption {
 	return func(ctr *Container) error {
 		if ctr.valid {
 			return define.ErrCtrFinalized
@@ -1346,6 +1346,7 @@ func WithRootFS(rootfs string) CtrCreateOption {
 			return err
 		}
 		ctr.config.Rootfs = rootfs
+		ctr.config.RootfsOverlay = overlay
 		return nil
 	}
 }