Implement support for cxgbit offload

Just like the 'iser' value within np/, save and restore the 'cxgbit' value.
However, the property is called 'offload'. This will let us handle other
offloads with the same property in the future if and when they are
supported.

Signed-off-by: Andy Grover <agrover@redhat.com>

doc/saveconfig.json.5

@@ -195,6 +195,8 @@ values are
 (number).
 .I iser
 (boolean) is an optional value to enable iSER.
+.I offload
+(boolean) is an optional value to enable hardware offload.
 
 .SS node_acls
 This contains information about explicit initiator LUN mappings.

rtslib/target.py

@@ -728,10 +728,27 @@ class NetworkPortal(CFSNode):
             if os.path.isfile(path):
                 raise RTSLibError("Cannot change iser")
 
+    def _get_offload(self):
+        try:
+            # only offload at the moment is cxgbit
+            return bool(int(fread("%s/cxgbit" % self.path)))
+        except IOError:
+            return False
+
+    def _set_offload(self, boolean):
+        path = "%s/cxgbit" % self.path
+        try:
+            fwrite(path, str(int(boolean)))
+        except IOError:
+            # b/w compat: don't complain if cxgbit entry is missing
+            if os.path.isfile(path):
+                raise RTSLibError("Cannot change offload")
+
     # NetworkPortal public stuff
 
     def delete(self):
         self.iser = False
+        self.offload = False
         super(NetworkPortal, self).delete()
 
     parent_tpg = property(_get_parent_tpg,
@@ -743,6 +760,9 @@ class NetworkPortal(CFSNode):
     iser = property(_get_iser, _set_iser,
                     doc="Get or set a boolean value representing if this " \
                         + "NetworkPortal supports iSER.")
+    offload = property(_get_offload, _set_offload,
+                    doc="Get or set a boolean value representing if this " \
+                        + "NetworkPortal supports offload.")
 
     @classmethod
     def setup(cls, tpg_obj, p, err_func):
@@ -756,6 +776,7 @@ class NetworkPortal(CFSNode):
         try:
             np = cls(tpg_obj, p['ip_address'], p['port'])
             np.iser = p.get('iser', False)
+            np.offload = p.get('offload', False)
         except (RTSLibError, KeyError) as e:
             err_func("Creating NetworkPortal object %s:%s failed: %s" %
                      (p['ip_address'], p['port'], e))
@@ -765,6 +786,7 @@ class NetworkPortal(CFSNode):
         d['port'] = self.port
         d['ip_address'] = self.ip_address
         d['iser'] = self.iser
+        d['offload'] = self.offload
         return d