configure runtime without store

some podman commands do not require the use of a container/image store.
in those cases, it is more effecient to not open the store, because that
results in having to also close the store which can be costly when the
system is under heavy write I/O loads.

Signed-off-by: baude <bbaude@redhat.com>

libpod/options.go

@@ -300,6 +300,15 @@ func WithTmpDir(dir string) RuntimeOption {
 	}
 }
 
+// WithNoStore sets a bool on the runtime that we do not need
+// any containers storage.
+func WithNoStore() RuntimeOption {
+	return func(rt *Runtime) error {
+		rt.noStore = true
+		return nil
+	}
+}
+
 // WithMaxLogSize sets the maximum size of container logs.
 // Positive sizes are limits in bytes, -1 is unlimited.
 func WithMaxLogSize(limit int64) RuntimeOption {

libpod/runtime.go

@@ -125,6 +125,9 @@ type Runtime struct {
 
 	// mechanism to read and write even logs
 	eventer events.Eventer
+
+	// noStore indicates whether we need to interact with a store or not
+	noStore bool
 }
 
 // RuntimeConfig contains configuration options used to set up the runtime
@@ -784,11 +787,14 @@ func makeRuntime(ctx context.Context, runtime *Runtime) (err error) {
 	var store storage.Store
 	if os.Geteuid() != 0 {
 		logrus.Debug("Not configuring container store")
+	} else if runtime.noStore {
+		logrus.Debug("No store required. Not opening container store.")
 	} else {
 		store, err = storage.GetStore(runtime.config.StorageConfig)
 		if err != nil {
 			return err
 		}
+		err = nil
 
 		defer func() {
 			if err != nil && store != nil {
@@ -1148,6 +1154,8 @@ func (r *Runtime) Shutdown(force bool) error {
 	}
 
 	var lastError error
+	// If no store was requested, it can bew nil and there is no need to
+	// attempt to shut it down
 	if r.store != nil {
 		if _, err := r.store.Shutdown(force); err != nil {
 			lastError = errors.Wrapf(err, "Error shutting down container storage")