DNM:objclass-sdk: make cls_zlog an optional build

Signed-off-by: Neha Ojha <nojha@redhat.com>

ceph.spec.in

@@ -723,6 +723,8 @@ Summary:        RADOS object class development kit
 Group:          Development/Libraries
 License:        LGPL-2.0
 Requires:       librados2-devel = %{epoch}:%{version}-%{release}
+BuildRequires:  protobuf-devel
+BuildRequires:  protobuf-compiler
 %description -n rados-objclass-dev
 This package contains libraries and headers needed to develop RADOS object
 class plugins.

debian/control

@@ -45,6 +45,8 @@ Build-Depends: bc,
                libudev-dev,
                libxml2-dev,
 	       lsb-release,
+               libprotobuf-dev,
+               protobuf-compiler,
                parted,
                pkg-config,
                python (>= 2.7),

doc/rados/api/objclass-sdk.rst

@@ -14,34 +14,46 @@ tree because they do not depend on any internal implementation of `Ceph`. This
 project decouples object class development from Ceph and encourages creation 
 and distribution of object classes as packages.
 
-In order to demonstrate the use of this framework, we have  two examples. The 
+In order to demonstrate the use of this framework, we have two examples. The 
 first one is called ``cls_sdk``, which is a very simple object class that 
 makes use of the SDK framework. This object class resides in the ``src/cls`` 
 directory. 
 
-The second example is a project called, `ZLog`, which is a strongly 
+The second example is a project called, 
+`ZLog <http://noahdesu.github.io/zlog/#>`_ , which is a strongly 
 consistent shared-log designed to run at high-performance over distributed 
-storage systems. `ZLog <https://github.com/noahdesu/zlog>`_ makes use of 
-`Ceph` as a storage backend to provide high performance and reliability. 
-`ZLog` was earlier dependent on `Ceph's` ``encoding.h`` interface. Now, this 
-dependency has been eliminated by means of `Google Protocol Buffers`. 
-Therefore, in order to use `ZLog` with `Ceph's Object Class SDK framework`, 
-users need to setup the appropriate `Protobuf Packages 
-<https://github.com/google/protobuf>`_, based on their platform.
-
+storage systems. `ZLog` makes use of `Ceph` as a storage backend to provide 
+high performance and reliability. `ZLog` was earlier dependent on `Ceph's` 
+``encoding.h`` interface. Now, this dependency has been eliminated by making 
+use of serialization and deserialization methods provided by `Google Protocol 
+Buffers`. `ZLog` can now be built using `Ceph's Object Class SDK framework` 
+and users only need to setup the appropriate `Protobuf Packages 
+<https://github.com/google/protobuf>`_, based on their platform. The 
+``cls_zlog`` plugin resides in the ``src/cls/`` directory as an example of an 
+object class that can be built by making using of the SDK interface. The 
+`ZLog` project and unittests reside 
+`here <https://github.com/noahdesu/zlog>`_. This project is evolving 
+and we are hoping to see a slightly different version of the plugin soon. 
 
 Installing objclass.h
 ---------------------
 
 The object class interface that enables out-of-tree development of object 
 classes resides in ``src/include/rados/`` and gets installed with `Ceph` 
-installation. It can be found in ``<prefix>/include/rados``. ::
+installation. After running ``make install``, you should be able to see it 
+in ``<prefix>/include/rados``. ::
 
         ls /usr/local/include/rados
 
-Using the SDK example
----------------------
+Using the SDK examples
+----------------------
 
-The ``cls_sdk`` object class resides in ``src/cls/sdk/``. This gets built and 
+1. The ``cls_sdk`` object class resides in ``src/cls/sdk/``. This gets built and 
 loaded into Ceph, with the Ceph build process. You can run the 
-``ceph_test_cls_sdk`` unittest to test this class.
+``ceph_test_cls_sdk`` unittest, which resides in ``src/test/cls_sdk/``, 
+to test this class.
+
+2. As for the ``cls_zlog`` object class, the plugin gets built and loaded into 
+`Ceph` with its build process. The unittests can be run separately by cloning 
+and building https://github.com/noahdesu/zlog and following the steps provided 
+in the documentation.

src/cls/CMakeLists.txt

@@ -9,15 +9,18 @@ set_target_properties(cls_sdk PROPERTIES VERSION "1.0.0" SOVERSION "1")
 install(TARGETS cls_sdk DESTINATION ${cls_dir})
 
 # cls_zlog
-find_package(Protobuf REQUIRED)
-include_directories(${PROTOBUF_INCLUDE_DIRS})
-PROTOBUF_GENERATE_CPP(PROTO_SRCS PROTO_HDRS zlog/zlog.proto)
-add_library(cls_zlog SHARED zlog/cls_zlog.cc ${PROTO_SRCS})
-target_include_directories(cls_zlog PUBLIC
-    ${PROTOBUF_INCLUDE_DIRS} ${CMAKE_CURRENT_BINARY_DIR})
-target_link_libraries(cls_zlog ${PROTOBUF_LIBRARIES})
-set_target_properties(cls_zlog PROPERTIES VERSION "1.0.0" SOVERSION "1")
-install(TARGETS cls_zlog DESTINATION ${cls_dir})
+option(WITH_ZLOG "build ZLog using the object class SDK" ON)
+if(WITH_ZLOG)
+  find_package(Protobuf REQUIRED)
+  include_directories(${PROTOBUF_INCLUDE_DIRS})
+  PROTOBUF_GENERATE_CPP(PROTO_SRCS PROTO_HDRS zlog/zlog.proto)
+  add_library(cls_zlog SHARED zlog/cls_zlog.cc ${PROTO_SRCS})
+  target_include_directories(cls_zlog PUBLIC
+      ${PROTOBUF_INCLUDE_DIRS} ${CMAKE_CURRENT_BINARY_DIR})
+  target_link_libraries(cls_zlog ${PROTOBUF_LIBRARIES})
+  set_target_properties(cls_zlog PROPERTIES VERSION "1.0.0" SOVERSION "1")
+  install(TARGETS cls_zlog DESTINATION ${cls_dir})
+endif(WITH_ZLOG)  
 
 # cls_hello
 set(cls_hello_srcs hello/cls_hello.cc)