Improve chroot driver by mounting proc

Add -driver flag to dockerinit

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Upstream-commit: 92e6db7beba8ad58e425119cc9885c355a5755e7
Component: engine

components/engine/mount/mount.go

@@ -25,27 +25,37 @@ func Mounted(mountpoint string) (bool, error) {
 	return false, nil
 }
 
-// Mount the specified options at the target path
+// Mount the specified options at the target path only if
+// the target is not mounted
 // Options must be specified as fstab style
 func Mount(device, target, mType, options string) error {
 	if mounted, err := Mounted(target); err != nil || mounted {
 		return err
 	}
+	return ForceMount(device, target, mType, options)
+}
 
+// Mount the specified options at the target path
+// reguardless if the target is mounted or not
+// Options must be specified as fstab style
+func ForceMount(device, target, mType, options string) error {
 	flag, data := parseOptions(options)
 	if err := mount(device, target, mType, uintptr(flag), data); err != nil {
 		return err
 	}
 	return nil
-
 }
 
 // Unmount the target only if it is mounted
-func Unmount(target string) (err error) {
+func Unmount(target string) error {
 	if mounted, err := Mounted(target); err != nil || !mounted {
 		return err
 	}
+	return ForceUnmount(target)
+}
 
+// Unmount the target reguardless if it is mounted or not
+func ForceUnmount(target string) (err error) {
 	// Simple retry logic for unmount
 	for i := 0; i < 10; i++ {
 		if err = unmount(target, 0); err == nil {