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, 7 insertions, 2 deletions

diff --git a/tools/lib/h5tools.h b/tools/lib/h5tools.h
index 9d065f3..dde4026 100644
--- a/tools/lib/h5tools.h
+++ b/tools/lib/h5tools.h
@@ -553,6 +553,7 @@ typedef struct h5tools_context_t {
  */
 
 typedef enum { VOL_BY_NAME, VOL_BY_VALUE } h5tools_vol_info_type_t;
+typedef enum { VFD_BY_NAME, VFD_BY_VALUE } h5tools_vfd_info_type_t;
 
 typedef struct h5tools_vol_info_t {
     h5tools_vol_info_type_t type;
@@ -568,12 +569,16 @@ typedef struct h5tools_vol_info_t {
 } h5tools_vol_info_t;
 
 typedef struct h5tools_vfd_info_t {
+    h5tools_vfd_info_type_t type;
 
     /* Pointer to information to be passed to the driver for its setup */
     const void *info;
 
-    /* Name of the VFD */
-    const char *name;
+    /* Field specifying either the driver's name or value (ID) */
+    union {
+        const char *       name;
+        H5FD_class_value_t value;
+    } u;
 } h5tools_vfd_info_t;
 
 /* This enum should match the entries in the above 'volnames'