cmake: allow use libzstd in system

since we are moving the test nodes from bionic to focal, we are able to
use the prebuilt libzstd libraries when running "make check". to speed
up the build and test, in this change:

* add FindZstd.cmake which allows us to use the libzstd in system
* extract BuildZstd.cmake for better readability
* add an option named "WITH_SYSTEM_ZSTD", which defaults to "OFF",
  so user can enable it on demand.

Signed-off-by: Kefu Chai <kchai@redhat.com>

cmake/modules/BuildZstd.cmake

@@ -0,0 +1,22 @@
+# libzstd - build it statically
+function(build_Zstd)
+  set(ZSTD_C_FLAGS "-fPIC -Wno-unused-variable -O3")
+
+  include(ExternalProject)
+  ExternalProject_Add(zstd_ext
+    SOURCE_DIR ${CMAKE_SOURCE_DIR}/src/zstd/build/cmake
+    CMAKE_ARGS -DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}
+               -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
+               -DCMAKE_C_FLAGS=${ZSTD_C_FLAGS}
+               -DCMAKE_AR=${CMAKE_AR}
+               -DCMAKE_POSITION_INDEPENDENT_CODE=${ENABLE_SHARED}
+    BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR}/libzstd
+    BUILD_COMMAND ${CMAKE_COMMAND} --build <BINARY_DIR> --target libzstd_static
+    BUILD_BYPRODUCTS "${CMAKE_CURRENT_BINARY_DIR}/libzstd/lib/libzstd.a"
+    INSTALL_COMMAND "")
+  add_library(Zstd::Zstd STATIC IMPORTED)
+  set_target_properties(Zstd::Zstd PROPERTIES
+    INTERFACE_INCLUDE_DIRECTORIES "${CMAKE_SOURCE_DIR}/src/zstd/lib"
+    IMPORTED_LOCATION "${CMAKE_CURRENT_BINARY_DIR}/libzstd/lib/libzstd.a")
+  add_dependencies(Zstd::Zstd zstd_ext)
+endfunction()

cmake/modules/FindZstd.cmake

@@ -0,0 +1,51 @@
+# Try to find liblz4
+#
+# Once done, this will define
+#
+# Zstd_FOUND
+# Zstd_INCLUDE_DIRS
+# Zstd_LIBRARIES
+# Zstd_VERSION_STRING
+# Zstd_VERSION_MAJOR
+# Zstd_VERSION_MINOR
+# Zstd_VERSION_RELEASE
+
+find_path(Zstd_INCLUDE_DIR
+  NAMES zstd.h
+  HINTS ${Zstd_ROOT_DIR}/include)
+
+if(Zstd_INCLUDE_DIR AND EXISTS "${Zstd_INCLUDE_DIR}/zstd.h")
+  foreach(ver "MAJOR" "MINOR" "RELEASE")
+    file(STRINGS "${Zstd_INCLUDE_DIR}/zstd.h" Zstd_VER_${ver}_LINE
+      REGEX "^#define[ \t]+ZSTD_VERSION_${ver}[ \t]+[0-9]+$")
+    string(REGEX REPLACE "^#define[ \t]+ZSTD_VERSION_${ver}[ \t]+([0-9]+)$"
+      "\\1" Zstd_VERSION_${ver} "${Zstd_VER_${ver}_LINE}")
+    unset(${Zstd_VER_${ver}_LINE})
+  endforeach()
+  set(Zstd_VERSION_STRING
+    "${Zstd_VERSION_MAJOR}.${Zstd_VERSION_MINOR}.${Zstd_VERSION_RELEASE}")
+endif()
+
+find_library(Zstd_LIBRARY
+  NAMES "${CMAKE_STATIC_LIBRARY_PREFIX}zstd.${CMAKE_STATIC_LIBRARY_SUFFIX}" zstd
+  HINTS ${Zstd_ROOT_DIR}/lib)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(Zstd
+  REQUIRED_VARS Zstd_LIBRARY Zstd_INCLUDE_DIR
+  VERSION_VAR Zstd_VERSION_STRING)
+
+mark_as_advanced(
+  Zstd_LIBRARY
+  Zstd_INCLUDE_DIR)
+
+if(Zstd_FOUND AND NOT (TARGET Zstd::Zstd))
+  set(Zstd_INCLUDE_DIRS ${Zstd_INCLUDE_DIR})
+  set(Zstd_LIBRARIES ${Zstd_LIBRARY})
+  add_library (Zstd::Zstd UNKNOWN IMPORTED)
+  set_target_properties(Zstd::Zstd PROPERTIES
+    INTERFACE_INCLUDE_DIRECTORIES ${Zstd_INCLUDE_DIR}
+    IMPORTED_LINK_INTERFACE_LANGUAGES "C"
+    IMPORTED_LOCATION ${Zstd_LIBRARY}
+    VERSION "${Zstd_VERSION_STRING}")
+endif()

src/compressor/zstd/CMakeLists.txt

@@ -1,33 +1,19 @@
 # zstd
 
-# libzstd - build it statically
-set(ZSTD_C_FLAGS "-fPIC -Wno-unused-variable -O3")
+option(WITH_SYSTEM_ZSTD "use prebuilt libzstd in system" OFF)
 
-include(ExternalProject)
-ExternalProject_Add(zstd_ext
-  SOURCE_DIR ${CMAKE_SOURCE_DIR}/src/zstd/build/cmake
-  CMAKE_ARGS -DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}
-             -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
-             -DCMAKE_C_FLAGS=${ZSTD_C_FLAGS}
-             -DCMAKE_AR=${CMAKE_AR}
-             -DCMAKE_POSITION_INDEPENDENT_CODE=${ENABLE_SHARED}
-  BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR}/libzstd
-  BUILD_COMMAND ${CMAKE_COMMAND} --build <BINARY_DIR> --target libzstd_static
-  BUILD_BYPRODUCTS "${CMAKE_CURRENT_BINARY_DIR}/libzstd/lib/libzstd.a"
-  INSTALL_COMMAND "")
-
-add_library(zstd STATIC IMPORTED)
-set_target_properties(zstd PROPERTIES
-  INTERFACE_INCLUDE_DIRECTORIES "${CMAKE_SOURCE_DIR}/src/zstd/lib"
-  IMPORTED_LOCATION "${CMAKE_CURRENT_BINARY_DIR}/libzstd/lib/libzstd.a")
-add_dependencies(zstd zstd_ext)
+if(WITH_SYSTEM_ZSTD)
+  find_package(Zstd 1.4.4 REQUIRED)
+else()
+  include(BuildZstd)
+  build_Zstd()
+endif()
 
 set(zstd_sources
-  CompressionPluginZstd.cc
-)
+  CompressionPluginZstd.cc)
 
 add_library(ceph_zstd SHARED ${zstd_sources})
-target_link_libraries(ceph_zstd PRIVATE zstd $<$<PLATFORM_ID:Windows>:ceph-common>)
+target_link_libraries(ceph_zstd PRIVATE Zstd::Zstd $<$<PLATFORM_ID:Windows>:ceph-common>)
 set_target_properties(ceph_zstd PROPERTIES
   VERSION 2.0.0
   SOVERSION 2