refine code, persistence use isolate method.

@@ -629,6 +629,11 @@ SrsConfDirective::~SrsConfDirective()
 
 SrsConfDirective* SrsConfDirective::copy()
 {
+    return copy("");
+}
+
+SrsConfDirective* SrsConfDirective::copy(string except)
+{
     SrsConfDirective* cp = new SrsConfDirective();
     
     cp->conf_line = conf_line;
@@ -637,7 +642,10 @@ SrsConfDirective* SrsConfDirective::copy()
     
     for (int i = 0; i < (int)directives.size(); i++) {
         SrsConfDirective* directive = directives.at(i);
-        cp->directives.push_back(directive->copy());
+        if (!except.empty() && directive->name == except) {
+            continue;
+        }
+        cp->directives.push_back(directive->copy(except));
     }
     
     return cp;
@@ -1982,8 +1990,8 @@ int SrsConfig::persistence()
         return ret;
     }
     
-    // persistence root directive to writer.
-    if ((ret = root->persistence(&fw, 0)) != ERROR_SUCCESS) {
+    // do persistence to writer.
+    if ((ret = do_persistence(&fw)) != ERROR_SUCCESS) {
         ::unlink(path.c_str());
         return ret;
     }
@@ -2000,6 +2008,18 @@ int SrsConfig::persistence()
     return ret;
 }
 
+int SrsConfig::do_persistence(SrsFileWriter* fw)
+{
+    int ret = ERROR_SUCCESS;
+    
+    // persistence root directive to writer.
+    if ((ret = root->persistence(fw, 0)) != ERROR_SUCCESS) {
+        return ret;
+    }
+    
+    return ret;
+}
+
 int SrsConfig::minimal_to_json(SrsJsonObject* obj)
 {
     int ret = ERROR_SUCCESS;

@@ -192,6 +192,8 @@ public:
      * so need to copy it to an old root directive, and use the copy result to do reload.
      */
     virtual SrsConfDirective* copy();
+    // @param except the name of sub directive.
+    virtual SrsConfDirective* copy(std::string except);
 // args
 public:
     /**
@@ -414,6 +416,9 @@ public:
      * persistence current config to file.
      */
     virtual int persistence();
+private:
+    virtual int do_persistence(SrsFileWriter* fw);
+public:
     /**
      * dumps the global sections to json.
      */