Make shared mount work in an initrd

config/types.go

@@ -94,6 +94,7 @@ type RancherConfig struct {
 	CloudInit           CloudInit                                 `yaml:"cloud_init,omitempty"`
 	Debug               bool                                      `yaml:"debug,omitempty"`
 	RmUsr               bool                                      `yaml:"rm_usr,omitempty"`
+	NoSharedRoot        bool                                      `yaml:"no_sharedroot,omitempty"`
 	Log                 bool                                      `yaml:"log,omitempty"`
 	ForceConsoleRebuild bool                                      `yaml:"force_console_rebuild,omitempty"`
 	Disable             []string                                  `yaml:"disable,omitempty"`

images/02-console/docker-init

@@ -19,4 +19,10 @@ for i in /opt/bin /usr/local/bin; do
     fi
 done
 
+mount --make-shared /
+
+if [ "$(grep '/var/lib/docker /var/lib/docker ' /proc/self/mountinfo | awk '{print $9}')" = "rootfs" ]; then
+    export DOCKER_RAMDISK=1
+fi
+
 exec /usr/bin/dockerlaunch $DOCKER_BIN "$@" $DOCKER_OPTS >>/var/log/docker.log 2>&1

init/init.go

@@ -11,6 +11,7 @@ import (
 	"syscall"
 
 	log "github.com/Sirupsen/logrus"
+	"github.com/docker/docker/pkg/mount"
 	"github.com/rancher/docker-from-scratch"
 	"github.com/rancher/os/config"
 	"github.com/rancher/os/util"
@@ -179,6 +180,28 @@ func isInitrd() bool {
 	return int64(stat.Type) == TMPFS_MAGIC || int64(stat.Type) == RAMFS_MAGIC
 }
 
+func setupSharedRoot(c *config.CloudConfig) (*config.CloudConfig, error) {
+	if !c.NoSharedRoot {
+		return c, nil
+	}
+
+	if isInitrd() {
+		for _, i := range []string{"/mnt", "/media"} {
+			if err := os.Mkdir(i, 0755); err != nil {
+				return c, err
+			}
+			if err := mount.Mount("tmpfs", i, "tmpfs", "rw"); err != nil {
+				return c, err
+			}
+			if err := mount.MakeRShared(i); err != nil {
+				return c, err
+			}
+		}
+		return c, nil
+	}
+	return c, mount.MakeShared("/")
+}
+
 func RunInit() error {
 	os.Setenv("PATH", "/sbin:/usr/sbin:/usr/bin")
 	if isInitrd() {
@@ -218,9 +241,7 @@ func RunInit() error {
 			return c, dockerlaunch.PrepareFs(&mountConfig)
 		},
 		initializeSelinux,
-		func(c *config.CloudConfig) (*config.CloudConfig, error) {
+		setupSharedRoot,
-			return c, syscall.Mount("", "/", "", syscall.MS_SHARED|syscall.MS_REC, "")
-		},
 		sysInit,
 	}