kernel-shark: Define build target for JSONC

Having the JSONC libs as a target simplifies the build/linking of
the KernelShark libraries and executables because all necessary
information, like include paths, compiler flags and library names
can be retriever directly from the target.

The patch also adds to FindJSONC.cmake the standard module
documentation header.

Link: https://lore.kernel.org/linux-trace-devel/20201211150756.577366-6-y.karadz@gmail.com

Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

3 files changed, 57 insertions, 19 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 007f46a6..a66050fa 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -26,8 +26,7 @@ include(${KS_DIR}/build/FindTraceCmd.cmake)
 set(CMAKE_MODULE_PATH "${KS_DIR}/build")
 find_package(TraceEvent REQUIRED)
 find_package(TraceFS    REQUIRED)
-
-include(${KS_DIR}/build/FindJSONC.cmake)
+find_package(JSONC      REQUIRED)
 
 find_package(Doxygen)
 
@@ -84,7 +83,6 @@ endif (CMAKE_BUILD_TYPE MATCHES Package)
 
 include_directories(${KS_DIR}/src/
                     ${KS_DIR}/build/src/
-                    ${JSONC_INCLUDE_DIR}
                     ${TRACECMD_INCLUDE_DIR})
 
 message("")
diff --git a/build/FindJSONC.cmake b/build/FindJSONC.cmake
index 3bae20fa..2d0d41f5 100644
--- a/build/FindJSONC.cmake
+++ b/build/FindJSONC.cmake
@@ -1,13 +1,44 @@
-# - Try to find json-c
-# https://cmake.org/Wiki/CMake:How_To_Find_Libraries
-# Once done this will define
-#  JSONC_FOUND - System has json-c
-#  JSONC_INCLUDE_DIRS - The json-c include directories
-#  JSONC_LIBRARIES - The libraries needed to use json-c
-#  JSONC_DEFINITIONS - Compiler switches required for using json-c
-
-find_package(PkgConfig)
+
+#[=======================================================================[.rst:
+FindJSONC
+-------
+
+Finds the traceevent library.
+
+Imported Targets
+^^^^^^^^^^^^^^^^
+
+This module defines the :prop_tgt:`IMPORTED` targets:
+
+``jsonc::jsonc``
+ Defined if the system has json-c.
+
+Result Variables
+^^^^^^^^^^^^^^^^
+
+``JSONC_FOUND``
+  True if the system has the json-c library.
+``JSONC_VERSION``
+  The version of the json-c library which was found.
+``JSONC_INCLUDE_DIRS``
+  Include directories needed to use json-c.
+``JSONC_LIBRARIES``
+  Libraries needed to link to json-c.
+
+Cache Variables
+^^^^^^^^^^^^^^^
+
+``JSONC_INCLUDE_DIR``
+  The directory containing ``json.h``.
+``JSONC_LIBRARY``
+  The path to the traceevent library.
+
+#]=======================================================================]
+
+find_package(PkgConfig QUIET)
 pkg_check_modules(PC_JSONC QUIET json-c)
+
+set(JSONC_VERSION     ${PC_JSONC_VERSION})
 set(JSONC_DEFINITIONS ${PC_JSONC_CFLAGS_OTHER})
 
 find_path(JSONC_INCLUDE_DIR json.h
@@ -20,19 +51,28 @@ find_library(JSONC_LIBRARY NAMES json-c libjson-c
 find_library(JSONC_LIBRARY NAMES json-c libjson-c
              HINTS ${PC_JSON-C_LIBDIR} ${PC_JSON-C_LIBRARY_DIRS})
 
+mark_as_advanced(JSONC_INCLUDE_DIR JSONC_LIBRARY)
+
 include(FindPackageHandleStandardArgs)
 # handle the QUIETLY and REQUIRED arguments and set JSONC_FOUND to TRUE
 # if all listed variables are TRUE
 find_package_handle_standard_args(JSONC DEFAULT_MSG
                                   JSONC_LIBRARY JSONC_INCLUDE_DIR)
 
-if (NOT JSONC_FOUND)
+if(JSONC_FOUND)
 
-  message(FATAL_ERROR "Json-C is Required!\n")
+  set(JSONC_LIBRARIES    ${JSONC_LIBRARY})
+  set(JSONC_INCLUDE_DIRS ${JSONC_INCLUDE_DIR})
 
-endif (NOT JSONC_FOUND)
+  if(NOT TARGET jsonc::jsonc)
+    add_library(jsonc::jsonc UNKNOWN IMPORTED)
 
-mark_as_advanced(JSONC_INCLUDE_DIR JSONC_LIBRARY)
+    set_target_properties(jsonc::jsonc
+                          PROPERTIES
+                            INTERFACE_INCLUDE_DIRECTORIES "${JSONC_INCLUDE_DIRS}"
+                            INTERFACE_COMPILE_DEFINITIONS "${JSONC_DEFINITIONS}"
+                            IMPORTED_LINK_INTERFACE_LANGUAGES "C"
+                            IMPORTED_LOCATION "${JSONC_LIBRARIES}")
+  endif()
 
-set(JSONC_LIBRARIES    ${JSONC_LIBRARY})
-set(JSONC_INCLUDE_DIRS ${JSONC_INCLUDE_DIR})
+endif()
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 7474e9db..213ce878 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -10,7 +10,7 @@ add_library(kshark SHARED libkshark.c
 target_link_libraries(kshark ${TRACECMD_LIBRARY}
                              trace::fs
                              trace::event
-                             ${JSONC_LIBRARY}
+                             jsonc::jsonc
                              ${CMAKE_DL_LIBS})
 
 set_target_properties(kshark  PROPERTIES SUFFIX	".so.${KS_VERSION_STRING}")