rootless: store only subset of storage.conf

do not store the entire file but only the subset of what we have
modified.  Also, we were not writing the correct data.  Since it is
not trivial to serialize storage.conf correctly and all the various
supported options, serialize only what we care about.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

pkg/util/utils.go

@@ -284,6 +284,35 @@ func GetRootlessStorageOpts() (storage.StoreOptions, error) {
 	return opts, nil
 }
 
+type tomlOptionsConfig struct {
+	MountProgram string `toml:"mount_program"`
+}
+
+type tomlConfig struct {
+	Storage struct {
+		Driver    string                      `toml:"driver"`
+		RunRoot   string                      `toml:"runroot"`
+		GraphRoot string                      `toml:"graphroot"`
+		Options   struct{ tomlOptionsConfig } `toml:"options"`
+	} `toml:"storage"`
+}
+
+func getTomlStorage(storeOptions *storage.StoreOptions) *tomlConfig {
+	config := new(tomlConfig)
+
+	config.Storage.Driver = storeOptions.GraphDriverName
+	config.Storage.RunRoot = storeOptions.RunRoot
+	config.Storage.GraphRoot = storeOptions.GraphRoot
+	for _, i := range storeOptions.GraphDriverOptions {
+		s := strings.Split(i, "=")
+		if s[0] == "overlay.mount_program" {
+			config.Storage.Options.MountProgram = s[1]
+		}
+	}
+
+	return config
+}
+
 // GetDefaultStoreOptions returns the storage ops for containers
 func GetDefaultStoreOptions() (storage.StoreOptions, error) {
 	storageOpts := storage.DefaultStoreOptions
@@ -304,9 +333,10 @@ func GetDefaultStoreOptions() (storage.StoreOptions, error) {
 				return storageOpts, errors.Wrapf(err, "cannot open %s", storageConf)
 			}
 
+			tomlConfiguration := getTomlStorage(&storageOpts)
 			defer file.Close()
 			enc := toml.NewEncoder(file)
-			if err := enc.Encode(storageOpts); err != nil {
+			if err := enc.Encode(tomlConfiguration); err != nil {
 				os.Remove(storageConf)
 			}
 		}