app-emulation/rkt: Backport overlay mount patch

https://github.com/rkt/rkt/issues/3805

sdk_container/src/third_party/coreos-overlay/app-emulation/rkt/files/rkt-1.28.1-avoid-double-overlay-mounts.patch

@@ -0,0 +1,109 @@
+From a778cd1b33d191e83178879cd23732f1c106a0ef Mon Sep 17 00:00:00 2001
+From: Luca Bruno <lucab@debian.org>
+Date: Wed, 20 Sep 2017 10:10:37 +0000
+Subject: [PATCH] stage0/gc: try to avoid double overlay mounts
+
+Before Linux 4.13, it used to be possible to perform double overlayfs
+mounts in place. This now fails at mount() with EBUSY.
+We were abusing this feature to unconditionally ensure that the stage1
+image overlay mount was present before calling gc entrypoint.
+This improves stage0 logic to perform the stage1 image overlay mount
+only if it doesn't already exist.
+---
+ rkt/gc.go | 50 ++++++++++++++++++++++++++++++++++++--------------
+ 1 file changed, 36 insertions(+), 14 deletions(-)
+
+diff --git a/rkt/gc.go b/rkt/gc.go
+index 5e025bb96..1ecdd8faf 100644
+--- a/rkt/gc.go
++++ b/rkt/gc.go
+@@ -26,6 +26,7 @@ import (
+ 
+ 	"github.com/hashicorp/errwrap"
+ 	"github.com/rkt/rkt/common"
++	"github.com/rkt/rkt/pkg/mountinfo"
+ 	pkgPod "github.com/rkt/rkt/pkg/pod"
+ 	"github.com/rkt/rkt/stage0"
+ 	"github.com/rkt/rkt/store/imagestore"
+@@ -197,29 +198,51 @@ func emptyGarbage() error {
+ 	return nil
+ }
+ 
+-func mountPodStage1(ts *treestore.Store, p *pkgPod.Pod) error {
++// mountPodStage1 tries to remount stage1 image overlay in case
++// it is not anymore available in place (e.g. a reboot happened
++// in-between). If an overlay mount is already there, we assume
++// stage1 image is properly in place and we don't perform any
++// further actions. A boolean is returned to signal whether a
++// a new mount was performed.
++func mountPodStage1(ts *treestore.Store, p *pkgPod.Pod) (bool, error) {
+ 	if !p.UsesOverlay() {
+-		return nil
++		return false, nil
+ 	}
+ 
+ 	s1Id, err := p.GetStage1TreeStoreID()
+ 	if err != nil {
+-		return errwrap.Wrap(errors.New("error getting stage1 treeStoreID"), err)
++		return false, errwrap.Wrap(errors.New("error getting stage1 treeStoreID"), err)
+ 	}
+ 	s1rootfs := ts.GetRootFS(s1Id)
+-
+ 	stage1Dir := common.Stage1RootfsPath(p.Path())
++
++	if mounts, err := mountinfo.ParseMounts(0); err == nil {
++		for _, m := range mounts {
++			if m.MountPoint == stage1Dir {
++				// stage1 image overlay already in place
++				return false, nil
++			}
++		}
++	}
++
+ 	overlayDir := filepath.Join(p.Path(), "overlay")
+ 	imgDir := filepath.Join(overlayDir, s1Id)
+ 	upperDir := filepath.Join(imgDir, "upper")
+ 	workDir := filepath.Join(imgDir, "work")
+ 
+ 	opts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", s1rootfs, upperDir, workDir)
+-	if err := syscall.Mount("overlay", stage1Dir, "overlay", 0, opts); err != nil {
+-		return errwrap.Wrap(errors.New("error mounting stage1"), err)
++	err = syscall.Mount("overlay", stage1Dir, "overlay", 0, opts)
++	if err != nil {
++		// -EBUSY means the overlay mount is already present.
++		// This behavior was introduced in Linux 4.13, double-mounts were allowed
++		// in older kernels.
++		if err == syscall.EBUSY {
++			stderr.Println("mount detected on stage1 target, skipping overlay mount")
++			return false, nil
++		}
++		return false, errwrap.Wrap(errors.New("error mounting stage1"), err)
+ 	}
+-
+-	return nil
++	return true, nil
+ }
+ 
+ // deletePod cleans up files and resource associated with the pod
+@@ -250,16 +273,15 @@ func deletePod(p *pkgPod.Pod) bool {
+ 			stage0.InitDebug()
+ 		}
+ 
+-		if err := mountPodStage1(ts, p); err == nil {
++		if newMount, err := mountPodStage1(ts, p); err == nil {
+ 			if err = stage0.GC(p.Path(), p.UUID, globalFlags.LocalConfigDir); err != nil {
+ 				stderr.PrintE(fmt.Sprintf("problem performing stage1 GC on %q", p.UUID), err)
+ 			}
+-			// an overlay fs can be mounted over itself, let's unmount it here
+-			// if we mounted it before to avoid problems when running
+-			// stage0.MountGC
+-			if p.UsesOverlay() {
++			// Linux <4.13 allows an overlay fs to be mounted over itself, so let's
++			// unmount it here to avoid problems when running stage0.MountGC
++			if p.UsesOverlay() && newMount {
+ 				stage1Mnt := common.Stage1RootfsPath(p.Path())
+-				if err := syscall.Unmount(stage1Mnt, 0); err != nil {
++				if err := syscall.Unmount(stage1Mnt, 0); err != nil && err != syscall.EBUSY {
+ 					stderr.PrintE("error unmounting stage1", err)
+ 				}
+ 			}

sdk_container/src/third_party/coreos-overlay/app-emulation/rkt/rkt-9999.ebuild

@@ -76,6 +76,8 @@ function add_stage1() {
 }
 
 src_prepare() {
+	epatch "${FILESDIR}/${PN}-1.28.1-avoid-double-overlay-mounts.patch"
+
 	# ensure we use a CoreOS PXE image version that matches rkt's expectations.
 	local rkt_coreos_version