BackendEngine: Added bookkeeping of custom_params of each backend to the base class. (#16)

* The backend plugin should not modify the passed parameters by the user, so the base
  class bookkeeps them and gives setter and getter methods to the plugin to access it.
* Now plugin can ask for value of a key, or add key/values for default parameters.
* Also added an API on the base class to return all the key/values, to be used in the
  agent API.
* Some rearragements in the base backend class to use protected when appropriate.
  Also the agent name is set only during construction and cannot be modified later.

Signed-off-by: Moein Khazraee <[email protected]>

Author: mkhazraee

include/backend/backend_engine.h

@@ -25,10 +25,51 @@
 // Base backend engine class for different backend implementations
 class nixlBackendEngine {
     private:
-        nixl_backend_t backendType;
+        // Members that cannot be modified by a child backend and parent bookkeep
+        nixl_backend_t   backendType;
+        nixl_b_params_t* customParams;
+
+    protected:
+        // Members that can be accessed by the child (localAgent cannot be modified)
+        bool              initErr;
+        const std::string localAgent;
+
+        nixl_status_t setInitParam(const std::string &key, const std::string &value) {
+            if (customParams->count(key)==0) {
+                (*customParams)[key] = value;
+                return NIXL_SUCCESS;
+            } else {
+                return NIXL_ERR_NOT_ALLOWED;
+            }
+        }
+
+        std::string getInitParam(const std::string &key) {
+            if (customParams->count(key)==0)
+                return "";
+            else
+                return (*customParams)[key];
+        }
 
     public:
+        nixlBackendEngine (const nixlBackendInitParams* init_params)
+            : localAgent(init_params->localAgent) {
+
+            this->backendType  = init_params->type;
+            this->initErr      = false;
+            this->customParams = new nixl_b_params_t(*(init_params->customParams));
+        }
+
+        virtual ~nixlBackendEngine () {
+            delete customParams;
+        }
+
+        bool getInitErr() { return initErr; }
         nixl_backend_t getType () const { return backendType; }
+        nixl_b_params_t getCustomParams () const { return *customParams; }
+
+        // The support function determine which methods are necessary by the child backend, and
+        // if they're called by mistake, they will return error if not implemented by backend.
+
         // Determines if a backend supports remote operations
         virtual bool supportsRemote () const = 0;
 
@@ -42,21 +83,6 @@ class nixlBackendEngine {
         // Determines if a backend supports progress thread.
         virtual bool supportsProgTh () const = 0;
 
-        // The support function determine which methods are necessary by the child backend, and
-        // if they're called by mistake, they will return error if not implemented by backend.
-
-        std::string    localAgent;
-        bool           initErr;
-
-        nixlBackendEngine (const nixlBackendInitParams* init_params) {
-            this->backendType = init_params->type;
-            this->localAgent  = init_params->localAgent;
-            this->initErr     = false;
-        }
-
-        virtual ~nixlBackendEngine () = default;
-
-        bool getInitErr() { return initErr; }
 
         // *** Pure virtual methods that need to be implemented by any backend *** //
 

include/nixl_types.h

@@ -41,7 +41,8 @@ typedef enum {
     NIXL_ERR_NOT_FOUND = -3,
     NIXL_ERR_NYI = -4,
     NIXL_ERR_MISMATCH = -5,
-    NIXL_ERR_BAD = -6
+    NIXL_ERR_BAD = -6,
+    NIXL_ERR_NOT_ALLOWED = -7
 } nixl_status_t;
 
 class nixlSerDes;

src/nixl_agent.cpp

@@ -92,7 +92,7 @@ nixlBackendH* nixlAgent::createBackend(const nixl_backend_t &type,
     nixl_status_t ret;
     std::string str;
 
-    // Registring same type of backend is not supported, unlikey and prob error
+    // Registering same type of backend is not supported, unlikely and prob error
     if (data->backendEngines.count(type)!=0)
         return nullptr;
 
@@ -116,7 +116,7 @@ nixlBackendH* nixlAgent::createBackend(const nixl_backend_t &type,
     }
 
     if (backend!=nullptr) {
-        if (backend->initErr) {
+        if (backend->getInitErr()) {
             delete backend;
             return nullptr;
         }
@@ -447,7 +447,7 @@ nixl_status_t nixlAgent::makeXferReq (const nixlXferSideH* local_side,
     // }
 
     // Populate has been already done, no benefit in having sorted descriptors
-    // which will be overwritten by [] assignement operator.
+    // which will be overwritten by [] assignment operator.
     nixlXferReqH *handle = new nixlXferReqH;
     handle->initiatorDescs = new nixl_meta_dlist_t (
                                      local_side->descs->getType(),