libpod: add GetConfigNoCopy()

Add a new function to libpod to directly access the runtime
configuration without creating an expensive deep copy.  Further migrate
a number of callers to this new function.

This drops the number of calls to JSONDeepCopy from 4 to 1 in a simple
`podman run --rm -d busybox top`.

Future work: Please note that there are more callers of GetConfig() that
can me migrated to GetConfigNoCopy().

[NO TESTS NEEDED]

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

libpod/runtime.go

@@ -706,19 +706,32 @@ func (r *Runtime) TmpDir() (string, error) {
 	return r.config.Engine.TmpDir, nil
 }
 
-// GetConfig returns a copy of the configuration used by the runtime
-func (r *Runtime) GetConfig() (*config.Config, error) {
+// GetConfig returns the configuration used by the runtime.
+// Note that the returned value is not a copy and must hence
+// only be used in a reading fashion.
+func (r *Runtime) GetConfigNoCopy() (*config.Config, error) {
 	r.lock.RLock()
 	defer r.lock.RUnlock()
 
 	if !r.valid {
 		return nil, define.ErrRuntimeStopped
 	}
+	return r.config, nil
+}
+
+// GetConfig returns a copy of the configuration used by the runtime.
+// Please use GetConfigNoCopy() in case you only want to read from
+// but not write to the returned config.
+func (r *Runtime) GetConfig() (*config.Config, error) {
+	rtConfig, err := r.GetConfigNoCopy()
+	if err != nil {
+		return nil, err
+	}
 
 	config := new(config.Config)
 
 	// Copy so the caller won't be able to modify the actual config
-	if err := JSONDeepCopy(r.config, config); err != nil {
+	if err := JSONDeepCopy(rtConfig, config); err != nil {
 		return nil, errors.Wrapf(err, "error copying config")
 	}
 

pkg/domain/infra/abi/secrets.go

@@ -21,7 +21,7 @@ func (ic *ContainerEngine) SecretCreate(ctx context.Context, name string, reader
 
 	// set defaults from config for the case they are not set by an upper layer
 	// (-> i.e. tests that talk directly to the api)
-	cfg, err := ic.Libpod.GetConfig()
+	cfg, err := ic.Libpod.GetConfigNoCopy()
 	if err != nil {
 		return nil, err
 	}

pkg/specgen/generate/container.go

@@ -54,7 +54,7 @@ func CompleteSpec(ctx context.Context, r *libpod.Runtime, s *specgen.SpecGenerat
 		}
 	}
 
-	rtc, err := r.GetConfig()
+	rtc, err := r.GetConfigNoCopy()
 	if err != nil {
 		return nil, err
 	}

pkg/specgen/generate/container_create.go

@@ -23,7 +23,7 @@ import (
 // Returns the created, container and any warnings resulting from creating the
 // container, or an error.
 func MakeContainer(ctx context.Context, rt *libpod.Runtime, s *specgen.SpecGenerator) (*spec.Spec, *specgen.SpecGenerator, []libpod.CtrCreateOption, error) {
-	rtc, err := rt.GetConfig()
+	rtc, err := rt.GetConfigNoCopy()
 	if err != nil {
 		return nil, nil, nil, err
 	}