path: root/release_docs/RELEASE.txt

HDF5 version 1.13.1-1 currently under development
================================================================================


INTRODUCTION
============

This document describes the differences between this release and the previous
HDF5 release. It contains information on the platforms tested and known
problems in this release. For more details check the HISTORY*.txt files in the
HDF5 source.

Note that documentation in the links below will be updated at the time of each
final release.

Links to HDF5 documentation can be found on The HDF5 web page:

     https://portal.hdfgroup.org/display/HDF5/HDF5

The official HDF5 releases can be obtained from:

     https://www.hdfgroup.org/downloads/hdf5/

Changes from Release to Release and New Features in the HDF5-1.13.x release series
can be found at:

     https://portal.hdfgroup.org/display/HDF5/HDF5+Application+Developer%27s+Guide

If you have any questions or comments, please send them to the HDF Help Desk:

     help@hdfgroup.org


CONTENTS
========

- New Features
- Support for new platforms and languages
- Bug Fixes since HDF5-1.12.0
- Platforms Tested
- Known Problems
- CMake vs. Autotools installations


New Features
============

    Configuration:
    -------------
    - Added new configure option to support building parallel tools.
      See Tools below (autotools - CMake):
            --enable-parallel-tools      HDF5_BUILD_PARALLEL_TOOLS

      (RAW - 2021/10/25)

    - Added new configure options to enable dimension scales APIs (H5DS*) to
      use new object references with the native VOL connector (aka native HDF5
      library). New references are always used for non-native terminal VOL
      connectors (e.g., DAOS).

      Autotools   --enable-dimension-scales-with-new-ref
      CMake       HDF5_DIMENSION_SCALES_NEW_REF=ON

      (EIP - 2021/10/25, HDFFV-11180)

    - Refactored the utils folder.

      Added subfolder test and moved the 'swmr_check_compat_vfd.c file'
      from test into utils/test. Deleted the duplicate swmr_check_compat_vfd.c
      file in hl/tools/h5watch folder. Also fixed vfd check options.

      (ADB - 2021/10/18)

    - Changed autotools and CMake configurations to derive both
      compilation warnings-as-errors and warnings-only-warn configurations
      from the same files, 'config/*/*error*'.  Removed redundant files
      'config/*/*noerror*'.

      (DCY - 2021/09/29)

    - Added new option to control the build of High-Level tools
      that default ON/enabled.

      Add configure options (autotools - CMake):
            --enable-hltools       HDF5_BUILD_HL_TOOLS

      Disabling this option prevents building the gif tool which
      contains the following CVEs:
          HDFFV-10592 CVE-2018-17433
          HDFFV-10593 CVE-2018-17436
          HDFFV-11048 CVE-2020-10809

      (ADB - 2021/09/16, HDFFV-11266)

    - Adds C++ Autotools configuration file for Intel

      * Checks for icpc as the compiler
      * Sets std=c++11
      * Copies most non-warning flags from intel-flags

      (DER - 2021/06/02)

    - Adds C++ Autotools configuration file for PGI

      * Checks for pgc++ as the compiler name (was: pgCC)
      * Sets -std=c++11
      * Other options basically match new C options (below)

      (DER - 2021/06/02)

    - Updates PGI C options

      * -Minform set to warn (was: inform) to suppress spurious messages
      * Sets -gopt -O2 as debug options
      * Sets -O4 as 'high optimization' option
      * Sets -O0 as 'no optimization' option
      * Removes specific settings for PGI 9 and 10

      (DER - 2021/06/02)

    - A C++11-compliant compiler is now required to build the C++ wrappers

      CMAKE_CXX_STANDARD is now set to 11 when building with CMake and
      -std=c++11 is added when building with clang/gcc via the Autotools.

      (DER - 2021/05/27)

    - CMake will now run the shell script tests in test/ by default

      The test directory includes several shell script tests that previously
      were not run by CMake. These are now run by default. TEST_SHELL_SCRIPTS
      has been set to ON and SH_PROGRAM has been set to bash (some test
      scripts use bash-isms). Platforms without bash (e.g., Windows) will
      ignore the script tests.

      (DER - 2021/05/23)

    - Removed unused HDF5_ENABLE_HSIZET option from CMake

      This has been unused for some time and has no effect.

      (DER - 2021/05/23)

    - CMake no longer builds the C++ library by default

      HDF5_BUILD_CPP_LIB now defaults to OFF, which is in line with the
      Autotools build defaults.

      (DER - 2021/04/20)

    - Removal of pre-VS2015 work-arounds

      HDF5 now requires Visual Studio 2015 or greater, so old work-around
      code and definitions have been removed, including:

      * <inttypes.h>
      * snprintf and vsnprintf
      * llround, llroundf, lround, lroundf, round, roundf
      * strtoll and strtoull
      * va_copy
      * struct timespec

      (DER - 2021/03/22)

    - Add CMake variable HDF5_LIB_INFIX

      This infix is added to all library names after 'hdf5'.
      e.g. the infix '_openmpi' results in the library name 'libhdf5_openmpi.so'
      This name is used in packages on debian based systems.
      (see https://packages.debian.org/jessie/amd64/libhdf5-openmpi-8/filelist)

      (barcode - 2021/03/22)

    - On macOS, Universal Binaries can now be built, allowing native execution on
      both Intel and Apple Silicon (ARM) based Macs.

      To do so, set CMAKE_OSX_ARCHITECTURES="x86_64;arm64"

      (SAM - 2021/02/07, github-311)

    - Added a configure-time option to control certain compiler warnings
      diagnostics

      A new configure-time option was added that allows some compiler warnings
      diagnostics to have the default operation. This is mainly intended for
      library developers and currently only works for gcc 10 and above. The
      diagnostics flags apply to C, C++ and Fortran compilers and will appear
      in "H5 C Flags", H5 C++ Flags" and H5 Fortran Flags, respectively. They
      will NOT be exported to h5cc, etc.

      The default is OFF, which will disable the warnings URL and color attributes
      for the warnings output. ON will not add the flags and allow default behavior.

      Autotools:    --enable-diags

      CMake:        HDF5_ENABLE_BUILD_DIAGS

      (ADB - 2021/02/05, HDFFV-11213)

    - CMake option to build the HDF filter plugins project as an external project

      The HDF filter plugins project is a collection of registered compression
      filters that can be dynamically loaded when needed to access data stored
      in a hdf5 file. This CMake-only option allows the plugins to be built and
      distributed with the hdf5 library and tools. Like the options for szip and
      zlib, either a tgz file or a git repository can be specified for the source.

      The option was refactored to use the CMake FetchContent process. This allows
      more control over the filter targets, but required external project command
      options to be moved to a CMake include file, HDF5PluginCache.cmake. Also
      enabled the filter examples to be used as tests for operation of the
      filter plugins.

      (ADB - 2020/12/10, OESS-98)

    - FreeBSD Autotools configuration now defaults to 'cc' and 'c++' compilers

      On FreeBSD, the autotools defaulted to 'gcc' as the C compiler and did
      not process C++ options. Since FreeBSD 10, the default compiler has
      been clang (via 'cc').

      The default compilers have been set to 'cc' for C and 'c++' for C++,
      which will pick up clang and clang++ respectively on FreeBSD 10+.
      Additionally, clang options are now set correctly for both C and C++
      and g++ options will now be set if that compiler is being used (an
      omission from the former functionality).

      (DER - 2020/11/28, HDFFV-11193)

    - Fixed POSIX problems when building w/ gcc on Solaris

      When building on Solaris using gcc, the POSIX symbols were not
      being set correctly, which could lead to issues like clock_gettime()
      not being found.

      The standard is now set to gnu99 when building with gcc on Solaris,
      which allows POSIX things to be #defined and linked correctly. This
      differs slightly from the gcc norm, where we set the standard to c99
      and manually set POSIX #define symbols.

      (DER - 2020/11/25, HDFFV-11191)

    - Added a configure-time option to consider certain compiler warnings
      as errors

      A new configure-time option was added that converts some compiler warnings
      to errors. This is mainly intended for library developers and currently
      only works for gcc and clang. The warnings that are considered errors
      will appear in the generated libhdf5.settings file. These warnings apply
      to C and C++ code and will appear in "H5 C Flags" and H5 C++ Flags",
      respectively. They will NOT be exported to h5cc, etc.

      The default is OFF. Building with this option may fail when compiling
      on operating systems and with compiler versions not commonly used by
      the library developers. Compilation may also fail when headers not
      under the control of the library developers (e.g., mpi.h, hdfs.h) raise
      warnings.

      Autotools:    --enable-warnings-as-errors

      CMake:        HDF5_ENABLE_WARNINGS_AS_ERRORS

      (DER - 2020/11/23, HDFFV-11189)

    - Autotools and CMake target added to produce doxygen generated documentation

      The default is OFF or disabled.
      Autoconf option is '--enable-doxygen'
        autotools make target is 'doxygen' and will build all doxygen targets
      CMake configure option is 'HDF5_BUILD_DOC'.
        CMake target is 'doxygen' for all available doxygen targets
        CMake target is 'hdf5lib_doc' for the src subdirectory

      (ADB - 2020/11/03)

    - CMake option to use MSVC naming conventions with MinGW

      HDF5_MSVC_NAMING_CONVENTION option enable to use MSVC naming conventions
      when using a MinGW toolchain

      (xan - 2020/10/30)

    - CMake option to statically link gcc libs with MinGW

      HDF5_MINGW_STATIC_GCC_LIBS allows to statically link libg/libstdc++
      with the MinGW toolchain

      (xan - 2020/10/30)

    - CMake option to build the HDF filter plugins project as an external project

      The HDF filter plugins project is a collection of registered compression
      filters that can be dynamically loaded when needed to access data stored
      in a hdf5 file. This CMake-only option allows the plugins to be built and
      distributed with the hdf5 library and tools. Like the options for szip and
      zlib, either a tgz file or a git repository can be specified for the source.

      The necessary options are (see the INSTALL_CMake.txt file):
        HDF5_ENABLE_PLUGIN_SUPPORT
        PLUGIN_TGZ_NAME or PLUGIN_GIT_URL
      There are more options necessary for various filters and the plugin project
      documents should be referenced.

      (ADB - 2020/09/27, OESS-98)

    - Added CMake option to format source files

      HDF5_ENABLE_FORMATTERS option will enable creation of targets using the
      pattern - HDF5_*_SRC_FORMAT - where * corresponds to the source folder
      or tool folder. All sources can be formatted by executing the format target;
      make format

      (ADB - 2020/08/24)

    - Add file locking configure and CMake options

      HDF5 1.10.0 introduced a file locking scheme, primarily to help
      enforce SWMR setup. Formerly, the only user-level control of the scheme
      was via the HDF5_USE_FILE_LOCKING environment variable.

      This change introduces configure-time options that control whether
      or not file locking will be used and whether or not the library
      ignores errors when locking has been disabled on the file system
      (useful on some HPC Lustre installations).

      In both the Autotools and CMake, the settings have the effect of changing
      the default property list settings (see the H5Pset/get_file_locking()
      entry, below).

      The yes/no/best-effort file locking configure setting has also been
      added to the libhdf5.settings file.

      Autotools:

        An --enable-file-locking=(yes|no|best-effort) option has been added.

        yes:          Use file locking.
        no:           Do not use file locking.
        best-effort:  Use file locking and ignore "disabled" errors.

      CMake:

        Two self-explanatory options have been added:

        HDF5_USE_FILE_LOCKING
        HDF5_IGNORE_DISABLED_FILE_LOCKS

        Setting both of these to ON is the equivalent to the Autotools'
        best-effort setting.

      NOTE:
      The precedence order of the various file locking control mechanisms is:

        1) HDF5_USE_FILE_LOCKING environment variable (highest)

        2) H5Pset_file_locking()

        3) configure/CMake options (which set the property list defaults)

        4) library defaults (currently best-effort)

      (DER - 2020/07/30, HDFFV-11092)

    - CMake option to link the generated Fortran MOD files into the include
      directory.

      The Fortran generation of MOD files by a Fortran compile can produce
      different binary files between SHARED and STATIC compiles with different
      compilers and/or different platforms. Note that it has been found that
      different versions of Fortran compilers will produce incompatible MOD
      files. Currently, CMake will locate these MOD files in subfolders of
      the include directory and add that path to the Fortran library target
      in the CMake config file, which can be used by the CMake find library
      process. For other build systems using the binary from a CMake install,
      a new CMake configuration can be used to copy the pre-chosen version
      of the Fortran MOD files into the install include directory.

      The default will depend on the configuration of
      BUILD_STATIC_LIBS and BUILD_SHARED_LIBS:
          YES                   YES         Default to SHARED
          YES                   NO          Default to STATIC
          NO                    YES         Default to SHARED
          NO                    NO          Default to SHARED
      The defaults can be overridden by setting the config option
          HDF5_INSTALL_MOD_FORTRAN to one of NO, SHARED, or STATIC

      (ADB - 2020/07/09, HDFFV-11116)

    - CMake option to use AEC (open source SZip) library instead of SZip

      The open source AEC library is a replacement library for SZip. In
      order to use it for hdf5 the libaec CMake source was changed to add
      "-fPIC" and exclude test files. Autotools does not build the
      compression libraries within hdf5 builds. New option USE_LIBAEC is
      required to compensate for the different files produced by AEC build.

      (ADB - 2020/04/22, OESS-65)

    - CMake ConfigureChecks.cmake file now uses CHECK_STRUCT_HAS_MEMBER

      Some handcrafted tests in HDFTests.c has been removed and the CMake
      CHECK_STRUCT_HAS_MEMBER module has been used.

      (ADB - 2020/03/24, TRILAB-24)

    - Both build systems use same set of warnings flags

      GNU C, C++ and gfortran warnings flags were moved to files in a config
      sub-folder named gnu-warnings. Flags that only are available for a specific
      version of the compiler are in files named with that version.
      Clang C warnings flags were moved to files in a config sub-folder
      named clang-warnings.
      Intel C, Fortran warnings flags were moved to files in a config sub-folder
      named intel-warnings.

      There are flags in named "error-xxx" files with warnings that may
      be promoted to errors. Some source files may still need fixes.

      There are also pairs of files named "developer-xxx" and "no-developer-xxx"
      that are chosen by the CMake option:HDF5_ENABLE_DEV_WARNINGS or the
      configure option:--enable-developer-warnings.

      In addition, CMake no longer applies these warnings for examples.

      (ADB - 2020/03/24, TRILAB-192)

    - Added test script for file size compare

      If CMake minimum version is at least 3.14, the fileCompareTest.cmake
      script will compare file sizes.

      (ADB - 2020/02/24, HDFFV-11036)

    - Update CMake minimum version to 3.12

      Updated CMake minimum version to 3.12 and added version checks
      for Windows features.

      (ADB - 2020/02/05, TRILABS-142)

    - Fixed CMake include properties for Fortran libraries

      Corrected the library properties for Fortran to use the
      correct path for the Fortran module files.

      (ADB - 2020/02/04, HDFFV-11012)

    - Added common warnings files for gnu and intel

      Added warnings files to use one common set of flags
      during configure for both autotools and CMake build
      systems. The initial implementation only affects a
      general set of flags for gnu and intel compilers.

      (ADB - 2020/01/17)

    - Added new options to CMake for control of testing

      Added CMake options (default ON);
        HDF5_TEST_SERIAL AND/OR HDF5_TEST_PARALLEL
        combined with:
          HDF5_TEST_TOOLS
          HDF5_TEST_EXAMPLES
          HDF5_TEST_SWMR
          HDF5_TEST_FORTRAN
          HDF5_TEST_CPP
          HDF5_TEST_JAVA

      (ADB - 2020/01/15, HDFFV-11001)

    - Added Clang sanitizers to CMake for analyzer support if compiler is clang.

      Added CMake code and files to execute the Clang sanitizers if
      HDF5_ENABLE_SANITIZERS is enabled and the USE_SANITIZER option
      is set to one of the following:
        Address
        Memory
        MemoryWithOrigins
        Undefined
        Thread
        Leak
        'Address;Undefined'

      (ADB - 2019/12/12, TRILAB-135)

    - Update CMake for VS2019 support

      CMake added support for VS2019 in version 3.15. Changes to the CMake
      generator setting required changes to scripts. Also updated version
      references in CMake files as necessary.

      (ADB - 2019/11/18, HDFFV-10962)

    - Update CMake options to match new autotools options

      Add configure options (autotools - CMake):
        enable-asserts       HDF5_ENABLE_ASSERTS
        enable-symbols       HDF5_ENABLE_SYMBOLS
        enable-profiling     HDF5_ENABLE_PROFILING
        enable-optimization  HDF5_ENABLE_OPTIMIZATION
      In addition NDEBUG is no longer forced defined and relies on the CMake
      process.

      (ADB - 2019/10/07, HDFFV-100901, HDFFV-10637, TRILAB-97)


    Library:
    --------
    - Adds new file driver-level memory copy operation for
      "ctl" callback and updates compact dataset I/O routines
      to utilize it

      When accessing an HDF5 file with a file driver that uses
      memory allocated in special ways (e.g., without standard
      library's `malloc`), a crash could be observed when HDF5
      tries to perform `memcpy` operations on such a memory
      region.

      These changes add a new H5FD_FEAT_MEMMANAGE VFD feature
      flag, which, if specified as supported by a VFD, will
      inform HDF5 that the VFD either uses special memory
      management routines or wishes to perform memory management
      in a specific way. Therefore, this flag instructs HDF5 to
      ask the file driver to perform memory management for
      certain operations.

      These changes also introduce a new "ctl" callback
      operation identified by the H5FD_CTL__MEM_COPY op code.
      This operation simply asks a VFD to perform a memory copy.
      The arguments to this operation are passed to the "ctl"
      callback's "input" parameter as a pointer to a struct
      defined as:

        struct H5FD_ctl_memcpy_args_t {
          void *      dstbuf;  /**< Destination buffer */
          hsize_t     dst_off; /**< Offset within destination buffer */
          const void *srcbuf;  /**< Source buffer */
          hsize_t     src_off; /**< Offset within source buffer */
          size_t      len;     /**< Length of data to copy from source buffer */
        } H5FD_ctl_memcpy_args_t;

      Further, HDF5's compact dataset I/O routines were
      identified as a problematic area that could cause a crash
      for VFDs that make use of special memory management. Those
      I/O routines were therefore updated to make use of this new
      "ctl" callback operation in order to ask the underlying
      file driver to correctly handle memory copies.

      (JTH - 2021/09/28)

    - Adds new "ctl" callback to VFD H5FD_class_t structure
      with the following prototype:

        herr_t (*ctl)(H5FD_t *file, uint64_t op_code,
                      uint64_t flags, const void *input,
                      void **output);

      This newly-added "ctl" callback allows Virtual File
      Drivers to intercept and handle arbitary operations
      identified by an operation code. Its parameters are
      as follows:

        `file` [in] - A pointer to the file to be operated on
        `op_code` [in] - The operation code identifying the
                         operation to be performed
        `flags` [in] - Flags governing the behavior of the
                       operation performed (see H5FDpublic.h
                       for a list of valid flags)
        `input` [in] - A pointer to arguments passed to the
                       VFD performing the operation
        `output` [out] - A pointer for the receiving VFD to
                         use for output from the operation

      (JRM - 2021/08/16)

    - Change how the release part of version, in major.minor.release is checked
      for compatibility

      The HDF5 library uses a function, H5check_version, to check that
      the version defined in the header files, which is used to compile an
      application is compatible with the version codified in the library, which
      the application loads at runtime. This previously required an exact match
      or the library would print a warning, dump the build settings and then
      abort or continue. An environment variable controlled the logic.

      Now the function first checks that the library release version, in
      major.minor.release, is not older than the version in the headers.
      Secondly, if the release version is different, it checks if either
      the library version or the header version is in the exception list, in
      which case the release part of version, in major.minor.release, must
      be exact. An environment variable still controls the logic.

      (ADB - 2021/07/27)

    - gcc warning suppression macros were moved out of H5public.h

      The HDF5 library uses a set of macros to suppress warnings on gcc.
      These warnings were originally located in H5public.h so that the
      multi VFD (which only uses public headers) could also make use of them
      but internal macros should not be publicly exposed like this.

      These macros have now been moved to H5private.h. Pending future multi
      VFD refactoring, the macros have been duplicated in H5FDmulti.c to
      suppress the format string warnings there.

      (DER - 2021/06/03)

    - H5Gcreate1() now rejects size_hint parameters larger than UINT32_MAX

      The size_hint value is ultimately stored in a uint32_t struct field,
      so specifying a value larger than this on a 64-bit machine can cause
      undefined behavior including crashing the system.

      The documentation for this API call was also incorrect, stating that
      passing a negative value would cause the library to use a default
      value. Instead, passing a "negative" value actually passes a very large
      value, which is probably not what the user intends and can cause
      crashes on 64-bit systems.

      The Doxygen documentation has been updated and passing values larger
      than UINT32_MAX for size_hint will now produce a normal HDF5 error.

      (DER - 2021/04/29, HDFFV-11241)


    - H5Pset_fapl_log() no longer crashes when passed an invalid fapl ID

      When passed an invalid fapl ID, H5Pset_fapl_log() would usually
      segfault when attempting to free an uninitialized pointer in the error
      handling code. This behavior is more common in release builds or
      when the memory sanitization checks were not selected as a build
      option.

      The pointer is now correctly initialized and the API call now
      produces a normal HDF5 error when fed an invalid fapl ID.

      (DER - 2021/04/28, HDFFV-11240)

    - Fixes a segfault when H5Pset_mdc_log_options() is called multiple times

      The call incorrectly attempts to free an internal copy of the previous
      log location string, which causes a segfault. This only happens
      when the call is invoked multiple times on the same property list.
      On the first call to a given fapl, the log location is set to NULL so
      the segfault does not occur.

      The string is now handled properly and the segfault no longer occurs.

      (DER - 2021/04/27, HDFFV-11239)

    - HSYS_GOTO_ERROR now emits the results of GetLastError() on Windows

      HSYS_GOTO_ERROR is an internal macro that is used to produce error
      messages when system calls fail. These strings include errno and the
      the associated strerror() value, which are not particularly useful
      when a Win32 API call fails.

      On Windows, this macro has been updated to include the result of
      GetLastError(). When a system call fails on Windows, usually only
      one of errno and GetLastError() will be useful, however we emit both
      for the user to parse. The Windows error message is not emitted as
      it would be awkward to free the FormatMessage() buffer given the
      existing HDF5 error framework. Users will have to look up the error
      codes in MSDN.

      The format string on Windows has been changed from:

        "%s, errno = %d, error message = '%s'"

      to:

        "%s, errno = %d, error message = '%s', Win32 GetLastError() = %"PRIu32""

      for those inclined to parse it for error values.

      (DER - 2021/03/21)

    - File locking now works on Windows

      Since version 1.10.0, the HDF5 library has used a file locking scheme
      to help enforce one reader at a time accessing an HDF5 file, which can
      be helpful when setting up readers and writers to use the single-
      writer/multiple-readers (SWMR) access pattern.

      In the past, this was only functional on POSIX systems where flock() or
      fcntl() were present. Windows used a no-op stub that always succeeded.

      HDF5 now uses LockFileEx() and UnlockFileEx() to lock the file using the
      same scheme as POSIX systems. We lock the entire file when we set up the
      locks (by passing DWORDMAX as both size parameters to LockFileEx()).

      (DER - 2021/03/19, HDFFV-10191)

    - H5Epush_ret() now requires a trailing semicolon

      H5Epush_ret() is a function-like macro that has been changed to
      contain a `do {} while(0)` loop. Consequently, a trailing semicolon
      is now required to end the `while` statement. Previously, a trailing
      semi would work, but was not mandatory. This change was made to allow
      clang-format to correctly format the source code.

      (SAM - 2021/03/03)

    - Improved performance of H5Sget_select_elem_pointlist

      Modified library to cache the point after the last block of points
      retrieved by H5Sget_select_elem_pointlist, so a subsequent call to the
      same function to retrieve the next block of points from the list can
      proceed immediately without needing to iterate over the point list.

      (NAF - 2021/01/19)

    - Replaced H5E_ATOM with H5E_ID in H5Epubgen.h

      The term "atom" is archaic and not in line with current HDF5 library
      terminology, which uses "ID" instead. "Atom" has mostly been purged
      from the library internals and this change removes H5E_ATOM from
      the H5Epubgen.h (exposed via H5Epublic.h) and replaces it with
      H5E_ID.

      (DER - 2020/11/24, HDFFV-11190)

    - Add a new public function H5Ssel_iter_reset

      This function resets a dataspace selection iterator back to an
      initial state so that it may be used for iteration once more.
      This can be useful when needing to iterate over a selection
      multiple times without having to repeatedly create/destroy
      a selection iterator for that dataspace selection.

      (JTH - 2020/09/18)

    - Remove HDFS VFD stubs

      The original implementation of the HDFS VFD included non-functional
      versions of the following public API calls when the HDFS VFD is
      not built as a part of the HDF5 library:

      * H5FD_hdfs_init()
      * H5Pget_fapl_hdfs()
      * H5Pset_fapl_hdfs()

      They will remain present in HDF5 1.10 and HDF5 1.12 releases
      for binary compatibility purposes but have been removed as of 1.14.0.

      Note that this has nothing to do with the real HDFS VFD API calls
      that are fully functional when the HDFS VFD is configured and built.

      We simply changed:

        #ifdef LIBHDFS
          <real API call>
        #else
          <useless stub>
        #endif

      to:

        #ifdef LIBHDFS
          <real API call>
        #endif

      Which is how the other optional VFDs are handled.

      (DER - 2020/08/27)

    - Add Mirror VFD

      Use TCP/IP sockets to perform write-only (W/O) file I/O on a remote
      machine. Must be used in conjunction with the Splitter VFD.

      (JOS - 2020/03/13, TBD)

    - Add Splitter VFD

      Maintain separate R/W and W/O channels for "concurrent" file writes
      to two files using a single HDF5 file handle.

      (JOS - 2020/03/13, TBD)

    - Refactored public exposure of haddr_t type in favor of "object tokens"

      To better accommodate HDF5 VOL connectors where "object addresses in a file"
      may not make much sense, the following changes were made to the library:

      * Introduced new H5O_token_t "object token" type, which represents a
        unique and permanent identifier for referencing an HDF5 object within
        a container; these "object tokens" are meant to replace object addresses.
        Along with the new type, a new H5Oopen_by_token API call was introduced
        to open an object by a token, similar to how object addresses were
        previously used with H5Oopen_by_addr.

      * Introduced new H5Lget_info2, H5Lget_info_by_idx2, H5Literate2, H5Literate_by_name2,
        H5Lvisit2 and H5Lvisit_by_name2 API calls, along with their associated H5L_info2_t
        struct and H5L_iterate2_t callback function, which work with the newly-introduced
        object tokens, instead of object addresses. The original functions have been
        renamed to version 1 functions and are deprecated in favor of the new version 2
        functions. The H5L_info_t and H5L_iterate_t types have been renamed to version 1
        types and are now deprecated in favor of their version 2 counterparts. For each of
        the functions and types, compatibility macros take place of the original symbols.

      * Introduced new H5Oget_info3, H5Oget_info_by_name3, H5Oget_info_by_idx3,
        H5Ovisit3 and H5Ovisit_by_name3 API calls, along with their associated H5O_info2_t
        struct and H5O_iterate2_t callback function, which work with the newly-introduced
        object tokens, instead of object addresses. The version 2 functions are now
        deprecated in favor of the version 3 functions. The H5O_info_t and H5O_iterate_t
        types have been renamed to version 1 types and are now deprecated in favor of their
        version 2 counterparts. For each, compatibility macros take place of the original
        symbols.

      * Introduced new H5Oget_native_info, H5Oget_native_info_by_name and
        H5Oget_native_info_by_idx API calls, along with their associated H5O_native_info_t
        struct, which are used to retrieve the native HDF5 file format-specific information
        about an object. This information (such as object header info and B-tree/heap info)
        has been removed from the new H5O_info2_t struct so that the more generic
        H5Oget_info(_by_name/_by_idx)3 routines will not try to retrieve it for non-native
        VOL connectors.

      * Added new H5Otoken_cmp, H5Otoken_to_str and H5Otoken_from_str routines to compare
        two object tokens, convert an object token into a nicely-readable string format and
        to convert an object token string back into a real object token, respectively.

      (DER, QAK, JTH - 2020/01/16)

    - Add new public function H5Sselect_adjust.

      This function shifts a dataspace selection by a specified logical offset
      within the dataspace extent.  This can be useful for VOL developers to
      implement chunked datasets.

      (NAF - 2019/11/18)

    - Add new public function H5Sselect_project_intersection.

      This function computes the intersection between two dataspace selections
      and projects that intersection into a third selection.  This can be useful
      for VOL developers to implement chunked or virtual datasets.

      (NAF - 2019/11/13, ID-148)

    - Add new public function H5VLget_file_type.

      This function returns a datatype equivalent to the supplied datatype but
      with the location set to be in the file.  This datatype can then be used
      with H5Tconvert to convert data between file and in-memory representation.
      This function is intended for use only by VOL connector developers.

      (NAF - 2019/11/08, ID-127)


    Parallel Library:
    -----------------
    -


    Fortran Library:
    ----------------
    - H5Fget_name_f fixed to handle correctly trailing whitespaces and
      newly allocated buffers.

      (MSB - 2021/08/30, github-826,972)

    - Add wrappers for H5Pset/get_file_locking() API calls

        h5pget_file_locking_f()
        h5pset_file_locking_f()

      See the configure option discussion for HDFFV-11092 (above) for more
      information on the file locking feature and how it's controlled.

      (DER - 2020/07/30, HDFFV-11092)

    C++ Library:
    ------------
    - Add wrappers for H5Pset/get_file_locking() API calls

        FileAccPropList::setFileLocking()
        FileAccPropList::getFileLocking()

      See the configure option discussion for HDFFV-11092 (above) for more
      information on the file locking feature and how it's controlled.

      (DER - 2020/07/30, HDFFV-11092)


    Java Library:
    -------------
    - Replaced HDF5AtomException with HDF5IdException

      Since H5E_ATOM changed to H5E_ID in the C library, the Java exception
      that wraps the error category was also renamed. Its functionality
      remains unchanged aside from the name.

      (See also the HDFFV-11190 note in the C library section)

      (DER - 2020/11/24, HDFFV-11190)

    - Added new H5S functions.

      H5Sselect_copy, H5Sselect_shape_same, H5Sselect_adjust,
      H5Sselect_intersect_block, H5Sselect_project_intersection,
      H5Scombine_hyperslab, H5Smodify_select, H5Scombine_select
      wrapper functions added.

      (ADB - 2020/10/27, HDFFV-10868)

    - Add wrappers for H5Pset/get_file_locking() API calls

        H5Pset_file_locking()
        H5Pget_use_file_locking()
        H5Pget_ignore_disabled_file_locking()

      Unlike the C++ and Fortran wrappers, there are separate getters for the
      two file locking settings, each of which returns a boolean value.

      See the configure option discussion for HDFFV-11092 (above) for more
      information on the file locking feature and how it's controlled.

      (DER - 2020/07/30, HDFFV-11092)

    - Added ability to test java library with VOLs.

      Created a new CMake script that combines the java and vol test scripts.

      (ADB - 2020/02/03, HDFFV-10996)

    - Tests fail for non-English locales.

      In the JUnit tests with a non-English locale, only the part before
      the decimal comma is replaced by XXXX and this leads to a comparison
      error. Changed the regex for the Time substitution.

      (ADB - 2020/01/09, HDFFV-10995)


    Tools:
    ------
    - Added a new (unix ONLY) parallel meta tool 'h5dwalk', which utilizes the
      mpifileutils (https://hpc.github.io/mpifileutils) open source utility
      library to enable parallel execution of other HDF5 tools.
      This approach can greatly enhance the serial hdf5 tool performance over large
      collections of files by utilizing MPI parallelism to distribute an application
      load over many independent MPI ranks and files.

      An introduction to the mpifileutils library and initial 'User Guide' for
      the new 'h5dwalk" tool can be found at:
      https://github.com/HDFGroup/hdf5doc/tree/master/RFCs/HDF5/tools/parallel_tools

      (RAW - 2021/10/25)

    - Refactored the perform tools and removed depends on test library.

      Moved the perf and h5perf tools from tools/test/perform to
      tools/src/h5perf so that they can be installed. This required
      that the test library dependency be removed by copying the
      needed functions from h5test.c.
      The standalone scripts and other perform tools remain in the
      tools/test/perform folder.

      (ADB - 2021/08/10)

    - Removed partial long exceptions

      Some of the tools accepted shortened versions of the long options
      (ex: --datas instead of --dataset). These were implemented inconsistently,
      are difficult to maintian, and occasionally block useful long option
      names. These partial long options have been removed from all the tools.

      (DER - 2021/08/03)

    - h5repack added help text for user-defined filters.

      Added help text line that states the valid values of the filter flag
      for user-defined filters;
          filter_flag: 1 is OPTIONAL or 0 is MANDATORY

      (ADB - 2021/01/14, HDFFV-11099)

    - Added h5delete tool

      Deleting HDF5 storage when using the VOL can be tricky when the VOL
      does not create files. The h5delete tool is a simple wrapper around
      the H5Fdelete() API call that uses the VOL specified in the
      HDF5_VOL_CONNECTOR environment variable to delete a "file". If
      the call to H5Fdelete() fails, the tool will attempt to use
      the POSIX remove(3) call to remove the file.

      Note that the HDF5 library does currently have support for
      H5Fdelete() in the native VOL connector.

      (DER - 2020/12/16)

    - h5repack added options to control how external links are handled.

      Currently h5repack preserves external links and cannot copy and merge
      data from the external files. Two options, merge and prune, were added to
      control how to merge data from an external link into the resulting file.
          --merge             Follow external soft link recursively and merge data.
          --prune             Do not follow external soft links and remove link.
          --merge --prune     Follow external link, merge data and remove dangling link.

      (ADB - 2020/08/05, HDFFV-9984)

    - h5repack was fixed to repack the reference attributes properly.
      The code line that checks if the update of reference inside a compound
      datatype is misplaced outside the code block loop that carries out the
      check. In consequence, the next attribute that is not the reference
      type was repacked again as the reference type and caused the failure of
      repacking. The fix is to move the corresponding code line to the correct
      code block.

       (KY -2020/02/07, HDFFV-11014)

    - h5diff was updated to use the new reference APIs.

       h5diff uses the new reference APIs to compare references.
       Attribute references can also be compared.

      (ADB - 2019/12/19, HDFFV-10980)

    - h5dump and h5ls were updated to use the new reference APIs.

      The tools library now use the new reference APIs to inspect a
      file. Also the DDL spec was updated to reflect the format
      changes produced with the new APIs. The export API and support
      functions in the JNI were updated to match.

      (ADB - 2019/12/06, HDFFV-10876 and HDFFV-10877)


    High-Level APIs:
    ----------------
    - added set/get for unsigned long long attributes

      The attribute writing high-level API has been expanded to include
      public set/get functions for ULL attributes, analogously to the
      existing set/get for other types.

      (AF - 2021/09/08)

    C Packet Table API:
    -------------------
    -

    Internal header file:
    ---------------------
    -

    Documentation:
    --------------
    -

Support for new platforms, languages and compilers
==================================================
    -

Bug Fixes since HDF5-1.12.0 release
===================================
    Library
    -------
    - Fixed an H5Pget_filter_by_id1/2() assert w/ out of range filter IDs

      Both H5Pget_filter_by_id1 and 2 did not range check the filter ID, which
      could trip as assert in debug versions of the library. The library now
      returns a normal HDF5 error when the filter ID is out of range.

      (DER - 2021/11/23, HDFFV-11286)

    - Fixed an issue with collective metadata reads being permanently disabled
      after a dataset chunk lookup operation. This would usually cause a
      mismatched MPI_Bcast and MPI_ERR_TRUNCATE issue in the library for
      simple cases of H5Dcreate() -> H5Dwrite() -> H5Dcreate().

      (JTH - 2021/11/08, HDFFV-11090)

    - Fixed cross platform incompatibility of references within variable length
      types

      Reference types within variable length types previously could not be
      read on a platform with different endianness from where they were
      written. Fixed so cross platform portability is restored.

      (NAF - 2021/09/30)

    - Detection of simple data transform function "x"

      In the case of the simple data transform function "x" the (parallel)
      library recognizes this is the same as not applying this data transform
      function. This improves the I/O performance. In the case of the parallel
      library, it also avoids breaking to independent I/O, which makes it
      possible to apply a filter when writing or reading data to or from
      the HDF5 file.

      (JWSB - 2021/09/13)

    - Fixed an invalid read and memory leak when parsing corrupt file space
      info messages

      When the corrupt file from CVE-2020-10810 was parsed by the library,
      the code that imports the version 0 file space info object header
      message to the version 1 struct could read past the buffer read from
      the disk, causing an invalid memory read. Not catching this error would
      cause downstream errors that eventually resulted in a previously
      allocated buffer to be unfreed when the library shut down. In builds
      where the free lists are in use, this could result in an infinite loop
      and SIGABRT when the library shuts down.

      We now track the buffer size and raise an error on attempts to read
      past the end of it.

      (DER - 2021/08/12, HDFFV-11053)


    - Fixed CVE-2018-14460

      The tool h5repack produced a segfault when the rank in dataspace
      message was corrupted, causing invalid read while decoding the
      dimension sizes.

      The problem was fixed by ensuring that decoding the dimension sizes
      and max values will not go beyong the end of the buffer.

      (BMR - 2021/05/12, HDFFV-11223)

    - Fixed CVE-2018-11206

      The tool h5dump produced a segfault when the size of a fill value
      message was corrupted and caused a buffer overflow.

      The problem was fixed by verifying the fill value's size
      against the buffer size before attempting to access the buffer.

      (BMR - 2021/03/15, HDFFV-10480)

    - Fixed CVE-2018-14033 (same issue as CVE-2020-10811)

      The tool h5dump produced a segfault when the storage size message
      was corrupted and caused a buffer overflow.

      The problem was fixed by verifying the storage size against the
      buffer size before attempting to access the buffer.

      (BMR - 2021/03/15, HDFFV-11159/HDFFV-11049)

    - Remove underscores on header file guards

      Header file guards used a variety of underscores at the beginning of the define.

      Removed all leading (some trailing) underscores from header file guards.

      (ADB - 2021/03/03, #361)

    - Fixed a segmentation fault

      A segmentation fault occurred with a Mathworks corrupted file.

      A detection of accessing a null pointer was added to prevent the problem.

      (BMR - 2021/02/19, HDFFV-11150)

    - Fixed issue with MPI communicator and info object not being
      copied into new FAPL retrieved from H5F_get_access_plist

      Added logic to copy the MPI communicator and info object into
      the output FAPL. MPI communicator is retrieved from the VFD, while
      the MPI info object is retrieved from the file's original FAPL.

      (JTH - 2021/02/15, HDFFV-11109)

    - Fixed problems with vlens and refs inside compound using
      H5VLget_file_type()

      Modified library to properly ref count H5VL_object_t structs and only
      consider file vlen and reference types to be equal if their files are
      the same.

      (NAF - 2021/01/22)

    - Fixed CVE-2018-17432

      The tool h5repack produced a segfault on a corrupted file which had
      invalid rank for scalar or NULL datatype.

      The problem was fixed by modifying the dataspace encode and decode
      functions to detect and report invalid rank. h5repack now fails
      with an error message for the corrupted file.

      (BMR - 2020/10/26, HDFFV-10590)

    - Creation of dataset with optional filter

      When the combination of type, space, etc doesn't work for filter
      and the filter is optional, it was supposed to be skipped but it was
      not skipped and the creation failed.

      Allowed the creation of the dataset in such a situation.

      (BMR - 2020/08/13, HDFFV-10933)

    - Explicitly declared dlopen to use RTLD_LOCAL

      dlopen documentation states that if neither RTLD_GLOBAL nor
      RTLD_LOCAL are specified, then the default behavior is unspecified.
      The default on linux is usually RTLD_LOCAL while macos will default
      to RTLD_GLOBAL.

      (ADB - 2020/08/12, HDFFV-11127)

    - H5Sset_extent_none() sets the dataspace class to H5S_NO_CLASS which
      causes asserts/errors when passed to other dataspace API calls.

      H5S_NO_CLASS is an internal class value that should not have been
      exposed via a public API call.

      In debug builds of the library, this can cause assert() function to
      trip. In non-debug builds, it will produce normal library errors.

      The new library behavior is for H5Sset_extent_none() to convert
      the dataspace into one of type H5S_NULL, which is better handled
      by the library and easier for developers to reason about.

      (DER - 2020/07/27, HDFFV-11027)

    - Fixed issues CVE-2018-13870 and CVE-2018-13869

      When a buffer overflow occurred because a name length was corrupted
      and became very large, h5dump crashed on memory access violation.

      A check for reading pass the end of the buffer was added to multiple
      locations to prevent the crashes and h5dump now simply fails with an
      error message when this error condition occurs.

      (BMR - 2020/07/22, HDFFV-11120 and HDFFV-11121)

    - Fixed the segmentation fault when reading attributes with multiple threads

      It was reported that the reading of attributes with variable length string
      datatype will crash with segmentation fault particularly when the number of
      threads is high (>16 threads).  The problem was due to the file pointer that
      was set in the variable length string datatype for the attribute.  That file
      pointer was already closed when the attribute was accessed.

      The problem was fixed by setting the file pointer to the current opened file pointer
      when the attribute was accessed.  Similar patch up was done before when reading
      dataset with variable length string datatype.

      (VC - 2020/07/13, HDFFV-11080)

    - Fixed CVE-2020-10810

      The tool h5clear produced a segfault during an error recovery in
      the superblock decoding.  An internal pointer was reset to prevent
      further accessing when it is not assigned with a value.

      (BMR - 2020/06/29, HDFFV-11053)

    - Fixed CVE-2018-17435

      The tool h52gif produced a segfault when the size of an attribute
      message was corrupted and caused a buffer overflow.

      The problem was fixed by verifying the attribute message's size
      against the buffer size before accessing the buffer.  h52gif was
      also fixed to display the failure instead of silently exiting
      after the segfault was eliminated.

      (BMR - 2020/06/19, HDFFV-10591)


    Java Library
    ------------
    - JNI utility function does not handle new references.

      The JNI utility function for converting reference data to string did
      not use the new APIs. In addition to fixing that function, added new
      java tests for using the new APIs.

      (ADB - 2021/02/16, HDFFV-11212)

    - The H5FArray.java class, in which virtually the entire execution time
      is spent using the HDFNativeData method that converts from an array
      of bytes to an array of the destination Java type.

        1. Convert the entire byte array into a 1-d array of the desired type,
           rather than performing 1 conversion per row;
        2. Use the Java Arrays method copyOfRange to grab the section of the
           array from (1) that is desired to be inserted into the destination array.

      (PGT,ADB - 2020/12/13, HDFFV-10865)

    - Added ability to test java library with VOLs.

      Created a new CMake script that combines the java and vol test scripts.

      (ADB - 2020/02/03, HDFFV-10996)

    - Tests fail for non-English locales.

      In the JUnit tests with a non-English locale, only the part before
      the decimal comma is replaced by XXXX and this leads to a comparison
      error. Changed the regex for the Time substitution.

      (ADB - 2020/01/09, HDFFV-10995)


    Configuration
    -------------
    - Corrected path searched by CMake find_package command

      The install path for cmake find_package files had been changed to use
        "share/cmake"
      for all platforms. However the trailing "hdf5" directory was not removed.
      This "hdf5" additional directory has been removed.

      (ADB - 2021/09/27)

    - Corrected pkg-config compile script

      It was discovered that the position of the "$@" argument for the command
      in the compile script may fail on some platforms and configurations. The
      position of the "$@"command argument was moved before the pkg-config sub command.

      (ADB - 2021/08/30)

    - Fixed CMake C++ compiler flags

      A recent refactoring of the C++ configure files accidently removed the
      file that executed the enable_language command for C++ needed by the
      HDFCXXCompilerFlags.cmake file. Also updated the intel warnings files,
      including adding support for windows platforms.

      (ADB - 2021/08/10)

    - Better support for libaec (open-source Szip library) in CMake

      Implemented better support for libaec 1.0.5 (or later) library. This version
      of libaec contains improvements for better integration with HDF5. Furthermore,
      the variable USE_LIBAEC_STATIC has been introduced to allow to make use of
      static version of libaec library. Use libaec_DIR or libaec_ROOT to set
      the location in which libaec can be found.

      Be aware, the Szip library of libaec 1.0.4 depends on another library within
      libaec library. This dependency is not specified in the current CMake
      configuration which means that one can not use the static Szip library of
      libaec 1.0.4 when building HDF5. This has been resolved in libaec 1.0.5.

      (JWSB - 2021/06/22)

    - Refactor CMake configure for Fortran

      The Fortran configure tests for KINDs reused a single output file that was
      read to form the Integer and Real Kinds defines. However, if config was run
      more then once, the CMake completed variable prevented the tests from executing
      again and the last value saved in the file was used to create the define.
      Creating separate files for each KIND solved the issue.

      In addition the test for H5_PAC_C_MAX_REAL_PRECISION was not pulling in
      defines for proper operation and did not define H5_PAC_C_MAX_REAL_PRECISION
      correctly for a zero value. This was fixed by supplying the required defines.
      In addition it was moved from the Fortran specific HDF5UseFortran.camke file
      to the C centric ConfigureChecks.cmake file.

      (ADB - 2021/06/03)

    - Move emscripten flag to compile flags

      The emscripten flag, -O0, was removed from target_link_libraries command
      to the correct target_compile_options command.

      (ADB - 2021/04/26 HDFFV-11083)

    - Remove arbitrary warning flag groups from CMake builds

      The arbitrary groups were created to reduce the quantity of warnings being
      reported that overwhelmed testing report systems. Considerable work has
      been accomplished to reduce the warning count and these arbitrary groups
      are no longer needed.
      Also the default for all warnings, HDF5_ENABLE_ALL_WARNINGS, is now ON.

      Visual Studio warnings C4100, C4706, and C4127 have been moved to
      developer warnings, HDF5_ENABLE_DEV_WARNINGS, and are disabled for normal builds.

      (ADB - 2021/03/22, HDFFV-11228)

    - Reclassify CMake messages, to allow new modes and --log-level option

      CMake message commands have a mode argument. By default, STATUS mode
      was chosen for any non-error message. CMake version 3.15 added additional
      modes, NOTICE, VERBOSE, DEBUG and TRACE. All message commands with a mode
      of STATUS were reviewed and most were reclassified as VERBOSE. The new
      mode was protected by a check for a CMake version of at least 3.15. If CMake
      version 3.17 or above is used, the user can use the command line option
      of "--log-level" to further restrict which message commands are displayed.

      (ADB - 2021/01/11, HDFFV-11144)

    - Fixes Autotools determination of the stat struct having an st_blocks field

      A missing parenthesis in an autoconf macro prevented building the test
      code used to determine if the stat struct contains the st_blocks field.
      Now that the test functions correctly, the H5_HAVE_STAT_ST_BLOCKS #define
      found in H5pubconf.h will be defined correctly on both the Autotools and
      CMake. This #define is only used in the tests and does not affect the
      HDF5 C library.

      (DER - 2021/01/07, HDFFV-11201)

    - Add missing ENV variable line to hdfoptions.cmake file

      Using the build options to use system SZIP/ZLIB libraries need to also
      specify the library root directory. Setting the {library}_ROOT ENV
      variable was added to the hdfoptions.cmake file.

      (ADB - 2020/10/19 HDFFV-11108)


    Tools
    -----
    - Changed how h5dump and h5ls identify long double.

      Long double support is not consistent across platforms. Tools will always
      identify long double as 128-bit [little/big]-endian float nn-bit precision.
      New test file created for datasets with attributes for float, double and
      long double. In addition any unknown integer or float datatype will now
      also show the number of bits for precision.
      These files are also used in the java tests.

      (ADB - 2021/03/24, HDFFV-11229,HDFFV-11113)

    - Fixed tools argument parsing.

      Tools parsing used the length of the option from the long array to match
      the option from the command line. This incorrectly matched a shorter long
      name option that happened to be a subset of another long option.
      Changed to match whole names.

      (ADB - 2021/01/19, HDFFV-11106)

    - The tools library was updated by standardizing the error stack process.

      General sequence is:
        h5tools_setprogname(PROGRAMNAME);
        h5tools_setstatus(EXIT_SUCCESS);
        h5tools_init();
        ... process the command-line (check for error-stack enable) ...
        h5tools_error_report();
        ... (do work) ...
        h5diff_exit(ret);

      (ADB - 2020/07/20, HDFFV-11066)

    - h5diff fixed a command line parsing error.

      h5diff would ignore the argument to -d (delta) if it is smaller than DBL_EPSILON.
      The macro H5_DBL_ABS_EQUAL was removed and a direct value comparision was used.

      (ADB - 2020/07/20, HDFFV-10897)

    - h5diff added a command line option to ignore attributes.

      h5diff would ignore all objects with a supplied path if the exclude-path argument is used.
      Adding the exclude-attribute argument will only exclude attributes, with the supplied path,
      from comparison.

      (ADB - 2020/07/20, HDFFV-5935)

    - h5diff added another level to the verbose argument to print filenames.

      Added verbose level 3 that is level 2 plus the filenames. The levels are:
        0 : Identical to '-v' or '--verbose'
        1 : All level 0 information plus one-line attribute status summary
        2 : All level 1 information plus extended attribute status report
        3 : All level 2 information plus file names

      (ADB - 2020/07/20, HDFFV-1005)

    - h5repack was fixed to repack the reference attributes properly.

      The code line that checks if the update of reference inside a compound
      datatype is misplaced outside the code block loop that carries out the
      check. In consequence, the next attribute that is not the reference
      type was repacked again as the reference type and caused the failure of
      repacking. The fix is to move the corresponding code line to the correct
      code block.

      (KY -2020/02/10, HDFFV-11014)

    - h5diff was updated to use the new reference APIs.

      h5diff uses the new reference APIs to compare references.
      Attribute references can also be compared.

      (ADB - 2019/12/19, HDFFV-10980)

    - h5dump and h5ls were updated to use the new reference APIs.

      The tools library now use the new reference APIs to inspect a
      file. Also the DDL spec was updated to reflect the format
      changes produced with the new APIs. The export API and support
      functions in the JNI were updated to match.

      (ADB - 2019/12/06, HDFFV-10876 and HDFFV-10877)


    Performance
    -------------
    -


    Fortran API
    -----------
    - Corrected INTERFACE INTENT(IN) to INTENT(OUT) for buf_size in h5fget_file_image_f.

      (MSB - 2020/02/18, HDFFV-11029)


    High-Level Library
    ------------------
    - Fixed HL_test_packet, test for packet table vlen of vlen.

      Incorrect length assignment.

      (ADB - 2021/10/14)


    Fortran High-Level APIs
    -----------------------
    -


    Documentation
    -------------
    -


    F90 APIs
    --------
    -


    C++ APIs
    --------
    - Added DataSet::operator=

      Some compilers complain if the copy constructor is given explicitly
      but the assignment operator is implicitly set to default.

      (2021/05/19)


    Testing
    -------
    - Stopped java/test/junit.sh.in installing libs for testing under ${prefix}

      Lib files needed are now copied to a subdirectory in the java/test
      directory, and on Macs the loader path for libhdf5.xxxs.so is changed
      in the temporary copy of libhdf5_java.dylib.

      (LRK, 2020/07/02, HDFFV-11063)


Platforms Tested
===================

    Linux 5.13.14-200.fc34           GNU gcc (GCC) 11.2.1 2021078 (Red Hat 11.2.1-1)
    #1 SMP x86_64  GNU/Linux         GNU Fortran (GCC) 11.2.1 2021078 (Red Hat 11.2.1-1)
    Fedora34                         clang version 12.0.1 (Fedora 12.0.1-1.fc34)
                                     (cmake and autotools)

    Linux 5.11.0-34-generic          GNU gcc (GCC) 9.3.0-17ubuntu1
    #36-Ubuntu SMP x86_64 GNU/Linux  GNU Fortran (GCC) 9.3.0-17ubuntu1
    Ubuntu 20.04                     Ubuntu clang version 10.0.0-4
                                     (cmake and autotools)

    Linux 5.8.0-63-generic           GNU gcc (GCC) 10.3.0-1ubuntu1
    #71-Ubuntu SMP x86_64 GNU/Linux  GNU Fortran (GCC) 10.3.0-1ubuntu1
    Ubuntu20.10                      Ubuntu clang version 11.0.0-2
                                     (cmake and autotools)

    Linux 5.3.18-22-default          GNU gcc (SUSE Linux) 7.5.0
    #1 SMP x86_64  GNU/Linux         GNU Fortran (SUSE Linux) 7.5.0
    SUSE15sp2                        clang version 7.0.1 (tags/RELEASE_701/final 349238)
                                     (cmake and autotools)

    Linux-4.14.0-115.21.2            spectrum-mpi/rolling-release
    #1 SMP ppc64le GNU/Linux             clang 8.0.1, 11.0.1
    (lassen)                             GCC 7.3.1
                                         XL 16.1.1.2
                                     (cmake)

    Linux-4.12.14-150.75-default     cray-mpich/7.7.10
    #1 SMP x86_64 GNU/Linux              GCC 7.3.0, 8.2.0
    (cori)                               Intel (R) Version 19.0.3.199
                                     (cmake)

    Linux-4.12.14-197.86-default     cray-mpich/7.7.6
    # 1SMP x86_64 GNU/Linux              GCC  7.3.0, 9.3.0, 10.2.0
    (mutrino)                            Intel (R) Version 17.0.4, 18.0.5, 19.1.3
                                     (cmake)

    Linux 3.10.0-1160.36.2.el7.ppc64 gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-39)
    #1 SMP ppc64be GNU/Linux         g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-39)
    Power8 (echidna)                 GNU Fortran (GCC) 4.8.5 20150623 (Red Hat 4.8.5-39)

    Linux 3.10.0-1160.24.1.el7       GNU C (gcc), Fortran (gfortran), C++ (g++)
    #1 SMP x86_64 GNU/Linux          compilers:
    Centos7                              Version 4.8.5 20150623 (Red Hat 4.8.5-4)
    (jelly/kituo/moohan)                 Version 4.9.3, Version 5.3.0, Version 6.3.0,
                                         Version 7.2.0, Version 8.3.0, Version 9.1.0
                                     Intel(R) C (icc), C++ (icpc), Fortran (icc)
                                     compilers:
                                         Version 17.0.0.098 Build 20160721
                                     GNU C (gcc) and C++ (g++) 4.8.5 compilers
                                         with NAG Fortran Compiler Release 6.1(Tozai)
                                     Intel(R) C (icc) and C++ (icpc) 17.0.0.098 compilers
                                         with NAG Fortran Compiler Release 6.1(Tozai)
                                     MPICH 3.1.4 compiled with GCC 4.9.3
                                     MPICH 3.3 compiled with GCC 7.2.0
                                     OpenMPI 2.1.6 compiled with icc 18.0.1
                                     OpenMPI 3.1.3 and 4.0.0 compiled with GCC 7.2.0
                                     PGI C, Fortran, C++ for 64-bit target on
                                     x86_64;
                                         Version 19.10-0

    Linux-3.10.0-1127.0.0.1chaos     openmpi-4.0.0
    #1 SMP x86_64 GNU/Linux              clang 6.0.0, 11.0.1
    (quartz)                             GCC 7.3.0, 8.1.0
                                         Intel 16.0.4, 18.0.2, 19.0.4

    macOS Apple M1 11.6              Apple clang version 12.0.5 (clang-1205.0.22.11)
    Darwin 20.6.0 arm64              gfortran GNU Fortran (Homebrew GCC 11.2.0) 11.1.0
    (macmini-m1)                     Intel icc/icpc/ifort version 2021.3.0 202106092021.3.0 20210609

    macOS Big Sur 11.3.1             Apple clang version 12.0.5 (clang-1205.0.22.9)
    Darwin 20.4.0 x86_64             gfortran GNU Fortran (Homebrew GCC 10.2.0_3) 10.2.0
    (bigsur-1)                       Intel icc/icpc/ifort version 2021.2.0 20210228

    macOS High Sierra 10.13.6        Apple LLVM version 10.0.0 (clang-1000.10.44.4)
    64-bit                           gfortran GNU Fortran (GCC) 6.3.0
    (bear)                           Intel icc/icpc/ifort version 19.0.4.233 20190416

    macOS Sierra 10.12.6             Apple LLVM version 9.0.0 (clang-900.39.2)
    64-bit                           gfortran GNU Fortran (GCC) 7.4.0
    (kite)                           Intel icc/icpc/ifort version 17.0.2

    Mac OS X El Capitan 10.11.6      Apple clang version 7.3.0 from Xcode 7.3
    64-bit                           gfortran GNU Fortran (GCC) 5.2.0
    (osx1011test)                    Intel icc/icpc/ifort version 16.0.2


    Linux 2.6.32-573.22.1.el6        GNU C (gcc), Fortran (gfortran), C++ (g++)
    #1 SMP x86_64 GNU/Linux          compilers:
    Centos6                              Version 4.4.7 20120313
    (platypus)                           Version 4.9.3, 5.3.0, 6.2.0
                                     MPICH 3.1.4 compiled with GCC 4.9.3
                                     PGI C, Fortran, C++ for 64-bit target on
                                     x86_64;
                                         Version 19.10-0

    Windows 10 x64                  Visual Studio 2015 w/ Intel C/C++/Fortran 18 (cmake)
                                    Visual Studio 2017 w/ Intel C/C++/Fortran 19 (cmake)
                                    Visual Studio 2019 w/ clang 12.0.0
                                        with MSVC-like command-line (C/C++ only - cmake)
                                    Visual Studio 2019 w/ Intel Fortran 19 (cmake)
                                    Visual Studio 2019 w/ MSMPI 10.1 (C only - cmake)


Known Problems
==============
    Setting a variable-length dataset fill value will leak the memory allocated
    for the p field of the hvl_t struct. A fix is in progress for this.
    HDFFV-10840

    CMake files do not behave correctly with paths containing spaces.
    Do not use spaces in paths because the required escaping for handling spaces
    results in very complex and fragile build files.
    ADB - 2019/05/07

    At present, metadata cache images may not be generated by parallel
    applications.  Parallel applications can read files with metadata cache
    images, but since this is a collective operation, a deadlock is possible
    if one or more processes do not participate.

    CPP ptable test fails on both VS2017 and VS2019 with Intel compiler, JIRA
    issue: HDFFV-10628.  This test will pass with VS2015 with Intel compiler.

    The subsetting option in ph5diff currently will fail and should be avoided.
    The subsetting option works correctly in serial h5diff.

    Known problems in previous releases can be found in the HISTORY*.txt files
    in the HDF5 source. Please report any new problems found to
    help@hdfgroup.org.


CMake vs. Autotools installations
=================================
While both build systems produce similar results, there are differences.
Each system produces the same set of folders on linux (only CMake works
on standard Windows); bin, include, lib and share. Autotools places the
COPYING and RELEASE.txt file in the root folder, CMake places them in
the share folder.

The bin folder contains the tools and the build scripts. Additionally, CMake
creates dynamic versions of the tools with the suffix "-shared". Autotools
installs one set of tools depending on the "--enable-shared" configuration
option.
  build scripts
  -------------
  Autotools: h5c++, h5cc, h5fc
  CMake: h5c++, h5cc, h5hlc++, h5hlcc

The include folder holds the header files and the fortran mod files. CMake
places the fortran mod files into separate shared and static subfolders,
while Autotools places one set of mod files into the include folder. Because
CMake produces a tools library, the header files for tools will appear in
the include folder.

The lib folder contains the library files, and CMake adds the pkgconfig
subfolder with the hdf5*.pc files used by the bin/build scripts created by
the CMake build. CMake separates the C interface code from the fortran code by
creating C-stub libraries for each Fortran library. In addition, only CMake
installs the tools library. The names of the szip libraries are different
between the build systems.

The share folder will have the most differences because CMake builds include
a number of CMake specific files for support of CMake's find_package and support
for the HDF5 Examples CMake project.

The issues with the gif tool are:
    HDFFV-10592 CVE-2018-17433
    HDFFV-10593 CVE-2018-17436
    HDFFV-11048 CVE-2020-10809
These CVE issues have not yet been addressed and can be avoided by not building
the gif tool. Disable building the High-Level tools with these options:
    autotools:   --disable-hltools
    cmake:       HDF5_BUILD_HL_TOOLS=OFF