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>

1 files changed, 16 insertions, 3 deletions

diff --git a/libpod/runtime.go b/libpod/runtime.go
index 161d5a533..27885bf5c 100644
--- a/libpod/runtime.go
+++ b/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")
 	}