VFD plugins (#602)

* Implement support for loading of Virtual File Drivers as plugins

Fix plugin caching for VOL connector and VFD plugins

Fix plugin iteration to skip paths that can't be opened

* Enable dynamic loading of VFDs with HDF5_DRIVER environment variable

* Temporarily disable error reporting during H5F_open double file open

* Default to using HDstat in h5_get_file_size for unknown VFDs

* Use macros for some environment variables that HDF5 interprets

* Update "null" and "ctl testing" VFDs

1 files changed, 52 insertions, 0 deletions

diff --git a/src/H5public.h b/src/H5public.h
index c9430dc..3e59e24 100644
--- a/src/H5public.h
+++ b/src/H5public.h
@@ -168,6 +168,58 @@
     (((H5_VERS_MAJOR == Maj) && (H5_VERS_MINOR == Min) && (H5_VERS_RELEASE <= Rel)) ||                       \
      ((H5_VERS_MAJOR == Maj) && (H5_VERS_MINOR < Min)) || (H5_VERS_MAJOR < Maj))
 
+/* Macros for various environment variables that HDF5 interprets */
+/**
+ * Used to specify the name of an HDF5 Virtual File Driver to use as
+ * the default file driver for file access. Setting this environment
+ * variable overrides the default file driver for File Access Property
+ * Lists.
+ */
+#define HDF5_DRIVER "HDF5_DRIVER"
+/**
+ * Used to specify a configuration string for the HDF5 Virtual File
+ * Driver being used for file access.
+ */
+#define HDF5_DRIVER_CONFIG "HDF5_DRIVER_CONFIG"
+/**
+ * Used to specify the name of an HDF5 Virtual Object Layer Connector
+ * to use as the default VOL connector for file access. Setting this
+ * environment variable overrides the default VOL connector for File
+ * Access Property Lists.
+ */
+#define HDF5_VOL_CONNECTOR "HDF5_VOL_CONNECTOR"
+/**
+ * Used to specify a delimiter-separated (currently, ';' for Windows
+ * and ':' for other systems) list of paths that HDF5 should search
+ * when loading plugins.
+ */
+#define HDF5_PLUGIN_PATH "HDF5_PLUGIN_PATH"
+/**
+ * Used to control the loading of HDF5 plugins at runtime. If this
+ * environment variable is set to the special string "::" (defined
+ * in H5PLpublic.h as H5PL_NO_PLUGIN), then dynamic loading of any
+ * HDF5 plugins will be disabled. No other values are valid for this
+ * environment variable.
+ */
+#define HDF5_PLUGIN_PRELOAD "HDF5_PLUGIN_PRELOAD"
+/**
+ * Used to control whether HDF5 uses file locking when creating or
+ * opening a file. Valid values for this environment variable are
+ * as follows:
+ *
+ *  "TRUE" or "1"  - Request that file locks should be used
+ *  "FALSE" or "0" - Request that file locks should NOT be used
+ *  "BEST_EFFORT"  - Request that file locks should be used and
+ *                     that any locking errors caused by file
+ *                     locking being disabled on the system
+ *                     should be ignored
+ */
+#define HDF5_USE_FILE_LOCKING "HDF5_USE_FILE_LOCKING"
+/**
+ * Used to instruct HDF5 not to cleanup files created during testing.
+ */
+#define HDF5_NOCLEANUP "HDF5_NOCLEANUP"
+
 /**
  * Status return values.  Failed integer functions in HDF5 result almost
  * always in a negative value (unsigned failing functions sometimes return