path: root/src/H5VLconnector.h

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright by The HDF Group.                                               *
 * All rights reserved.                                                      *
 *                                                                           *
 * This file is part of HDF5.  The full HDF5 copyright notice, including     *
 * terms governing use, modification, and redistribution, is contained in    *
 * the COPYING file, which can be found at the root of the source code       *
 * distribution tree, or in https://support.hdfgroup.org/ftp/HDF5/releases.  *
 * If you do not have access to either file, you may request a copy from     *
 * help@hdfgroup.org.                                                        *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/*
 * This file contains public declarations for authoring VOL connectors.
 */

#ifndef _H5VLconnector_H
#define _H5VLconnector_H

/* Public headers needed by this file */
#include "H5public.h"   /* Generic Functions                    */
#include "H5Apublic.h"  /* Attributes                           */
#include "H5ESpublic.h" /* Event Stack                          */
#include "H5Fpublic.h"  /* Files                                */
#include "H5Ipublic.h"  /* IDs                                  */
#include "H5Lpublic.h"  /* Links                                */
#include "H5Opublic.h"  /* Objects                              */
#include "H5Rpublic.h"  /* References                           */
#include "H5VLpublic.h" /* Virtual Object Layer                 */

/*****************/
/* Public Macros */
/*****************/

/* Capability flags for connector */
#define H5VL_CAP_FLAG_NONE       0    /* No special connector capabilities */
#define H5VL_CAP_FLAG_THREADSAFE 0x01 /* Connector is threadsafe */

/* Container info version */
#define H5VL_CONTAINER_INFO_VERSION 0x01 /* Container info struct version */

/* The maximum size allowed for blobs */
#define H5VL_MAX_BLOB_ID_SIZE (16) /* Allow for 128-bits blob IDs */

/*******************/
/* Public Typedefs */
/*******************/

/* types for attribute GET callback */
typedef enum H5VL_attr_get_t {
    H5VL_ATTR_GET_ACPL,         /* creation property list              */
    H5VL_ATTR_GET_INFO,         /* info                                */
    H5VL_ATTR_GET_NAME,         /* access property list                */
    H5VL_ATTR_GET_SPACE,        /* dataspace                           */
    H5VL_ATTR_GET_STORAGE_SIZE, /* storage size                        */
    H5VL_ATTR_GET_TYPE          /* datatype                            */
} H5VL_attr_get_t;

/* types for attribute SPECFIC callback */
typedef enum H5VL_attr_specific_t {
    H5VL_ATTR_DELETE, /* H5Adelete(_by_name/idx)             */
    H5VL_ATTR_EXISTS, /* H5Aexists(_by_name)                 */
    H5VL_ATTR_ITER,   /* H5Aiterate(_by_name)                */
    H5VL_ATTR_RENAME  /* H5Arename(_by_name)                 */
} H5VL_attr_specific_t;

/* Typedef for VOL connector attribute optional VOL operations */
typedef int H5VL_attr_optional_t;

/* types for dataset GET callback */
typedef enum H5VL_dataset_get_t {
    H5VL_DATASET_GET_DAPL,         /* access property list                */
    H5VL_DATASET_GET_DCPL,         /* creation property list              */
    H5VL_DATASET_GET_SPACE,        /* dataspace                           */
    H5VL_DATASET_GET_SPACE_STATUS, /* space status                        */
    H5VL_DATASET_GET_STORAGE_SIZE, /* storage size                        */
    H5VL_DATASET_GET_TYPE          /* datatype                            */
} H5VL_dataset_get_t;

/* types for dataset SPECFIC callback */
typedef enum H5VL_dataset_specific_t {
    H5VL_DATASET_SET_EXTENT, /* H5Dset_extent                       */
    H5VL_DATASET_FLUSH,      /* H5Dflush                            */
    H5VL_DATASET_REFRESH     /* H5Drefresh                          */
} H5VL_dataset_specific_t;

/* Typedef for VOL connector dataset optional VOL operations */
typedef int H5VL_dataset_optional_t;

/* types for datatype GET callback */
typedef enum H5VL_datatype_get_t {
    H5VL_DATATYPE_GET_BINARY, /* get serialized form of transient type    */
    H5VL_DATATYPE_GET_TCPL    /* datatype creation property list          */
} H5VL_datatype_get_t;

/* types for datatype SPECFIC callback */
typedef enum H5VL_datatype_specific_t { H5VL_DATATYPE_FLUSH, H5VL_DATATYPE_REFRESH } H5VL_datatype_specific_t;

/* Typedef and values for native VOL connector named datatype optional VOL operations */
typedef int H5VL_datatype_optional_t;
/* (No optional named datatype VOL operations currently) */

/* types for file GET callback */
typedef enum H5VL_file_get_t {
    H5VL_FILE_GET_CONT_INFO, /* file get container info              */
    H5VL_FILE_GET_FAPL,      /* file access property list            */
    H5VL_FILE_GET_FCPL,      /* file creation property list          */
    H5VL_FILE_GET_FILENO,    /* file number                          */
    H5VL_FILE_GET_INTENT,    /* file intent                          */
    H5VL_FILE_GET_NAME,      /* file name                            */
    H5VL_FILE_GET_OBJ_COUNT, /* object count in file                 */
    H5VL_FILE_GET_OBJ_IDS    /* object ids in file                   */
} H5VL_file_get_t;

/* types for file SPECIFIC callback */
typedef enum H5VL_file_specific_t {
    H5VL_FILE_FLUSH,         /* Flush file                       */
    H5VL_FILE_REOPEN,        /* Reopen the file                  */
    H5VL_FILE_MOUNT,         /* Mount a file                     */
    H5VL_FILE_UNMOUNT,       /* Unmount a file                   */
    H5VL_FILE_IS_ACCESSIBLE, /* Check if a file is accessible    */
    H5VL_FILE_DELETE,        /* Delete a file                    */
    H5VL_FILE_IS_EQUAL       /* Check if two files are the same  */
} H5VL_file_specific_t;

/* Typedef for VOL connector file optional VOL operations */
typedef int H5VL_file_optional_t;

/* types for group GET callback */
typedef enum H5VL_group_get_t {
    H5VL_GROUP_GET_GCPL, /* group creation property list     */
    H5VL_GROUP_GET_INFO  /* group info                       */
} H5VL_group_get_t;

/* types for group SPECFIC callback */
typedef enum H5VL_group_specific_t { H5VL_GROUP_FLUSH, H5VL_GROUP_REFRESH } H5VL_group_specific_t;

/* Typedef for VOL connector group optional VOL operations */
typedef int H5VL_group_optional_t;

/* link create types for VOL */
typedef enum H5VL_link_create_type_t {
    H5VL_LINK_CREATE_HARD,
    H5VL_LINK_CREATE_SOFT,
    H5VL_LINK_CREATE_UD
} H5VL_link_create_type_t;

/* types for link GET callback */
typedef enum H5VL_link_get_t {
    H5VL_LINK_GET_INFO, /* link info                         */
    H5VL_LINK_GET_NAME, /* link name                         */
    H5VL_LINK_GET_VAL   /* link value                        */
} H5VL_link_get_t;

/* types for link SPECIFIC callback */
typedef enum H5VL_link_specific_t {
    H5VL_LINK_DELETE, /* H5Ldelete(_by_idx)                */
    H5VL_LINK_EXISTS, /* link existence                    */
    H5VL_LINK_ITER    /* H5Literate/visit(_by_name)              */
} H5VL_link_specific_t;

/* Typedef and values for native VOL connector link optional VOL operations */
typedef int H5VL_link_optional_t;
/* (No optional link VOL operations currently) */

/* types for object GET callback */
typedef enum H5VL_object_get_t {
    H5VL_OBJECT_GET_FILE, /* object file                       */
    H5VL_OBJECT_GET_NAME, /* object name                       */
    H5VL_OBJECT_GET_TYPE, /* object type                       */
    H5VL_OBJECT_GET_INFO  /* H5Oget_info(_by_idx|name)         */
} H5VL_object_get_t;

/* types for object SPECIFIC callback */
typedef enum H5VL_object_specific_t {
    H5VL_OBJECT_CHANGE_REF_COUNT, /* H5Oincr/decr_refcount             */
    H5VL_OBJECT_EXISTS,           /* H5Oexists_by_name                 */
    H5VL_OBJECT_LOOKUP,           /* Lookup object                     */
    H5VL_OBJECT_VISIT,            /* H5Ovisit(_by_name)                */
    H5VL_OBJECT_FLUSH,            /* H5{D|G|O|T}flush                  */
    H5VL_OBJECT_REFRESH           /* H5{D|G|O|T}refresh                */
} H5VL_object_specific_t;

/* Typedef for VOL connector object optional VOL operations */
typedef int H5VL_object_optional_t;

/* types for async request SPECIFIC callback */
typedef enum H5VL_request_specific_t {
    H5VL_REQUEST_WAITANY,  /* Wait until any request completes */
    H5VL_REQUEST_WAITSOME, /* Wait until at least one requesst completes */
    H5VL_REQUEST_WAITALL   /* Wait until all requests complete */
} H5VL_request_specific_t;

/* Typedef and values for native VOL connector request optional VOL operations */
typedef int H5VL_request_optional_t;
/* (No optional request VOL operations currently) */

/* types for 'blob' SPECIFIC callback */
typedef enum H5VL_blob_specific_t {
    H5VL_BLOB_DELETE,  /* Delete a blob (by ID) */
    H5VL_BLOB_GETSIZE, /* Get size of blob */
    H5VL_BLOB_ISNULL,  /* Check if a blob ID is "null" */
    H5VL_BLOB_SETNULL  /* Set a blob ID to the connector's "null" blob ID value */
} H5VL_blob_specific_t;

/* Typedef and values for native VOL connector blob optional VOL operations */
typedef int H5VL_blob_optional_t;
/* (No optional blob VOL operations currently) */

/* Types for different ways that objects are located in an HDF5 container */
typedef enum H5VL_loc_type_t {
    H5VL_OBJECT_BY_SELF,
    H5VL_OBJECT_BY_NAME,
    H5VL_OBJECT_BY_IDX,
    H5VL_OBJECT_BY_TOKEN
} H5VL_loc_type_t;

typedef struct H5VL_loc_by_name {
    const char *name;
    hid_t       lapl_id;
} H5VL_loc_by_name_t;

typedef struct H5VL_loc_by_idx {
    const char *    name;
    H5_index_t      idx_type;
    H5_iter_order_t order;
    hsize_t         n;
    hid_t           lapl_id;
} H5VL_loc_by_idx_t;

typedef struct H5VL_loc_by_token {
    H5O_token_t *token;
} H5VL_loc_by_token_t;

/* Structure to hold parameters for object locations.
 * Either: BY_SELF, BY_NAME, BY_IDX, BY_TOKEN
 *
 * Note: Leave loc_by_token as the first union member so we
 *       can perform the simplest initialization of the struct
 *       without raising warnings.
 *
 * Note: BY_SELF requires no union members.
 */
typedef struct H5VL_loc_params_t {
    H5I_type_t      obj_type;
    H5VL_loc_type_t type;
    union {
        H5VL_loc_by_token_t loc_by_token;
        H5VL_loc_by_name_t  loc_by_name;
        H5VL_loc_by_idx_t   loc_by_idx;
    } loc_data;
} H5VL_loc_params_t;

/* Info for H5VL_FILE_GET_CONT_INFO */
typedef struct H5VL_file_cont_info_t {
    unsigned version;       /* version information (keep first) */
    uint64_t feature_flags; /* Container feature flags          */
                            /* (none currently defined)         */
    size_t token_size;      /* Size of tokens                   */
    size_t blob_id_size;    /* Size of blob IDs                 */
} H5VL_file_cont_info_t;

/* VOL connector info fields & callbacks */
typedef struct H5VL_info_class_t {
    size_t size;                     /* Size of the VOL info                         */
    void *(*copy)(const void *info); /* Callback to create a copy of the VOL info    */
    herr_t (*cmp)(int *cmp_value, const void *info1, const void *info2); /* Callback to compare VOL info */
    herr_t (*free)(void *info);                     /* Callback to release a VOL info               */
    herr_t (*to_str)(const void *info, char **str); /* Callback to serialize connector's info into a string */
    herr_t (*from_str)(const char *str,
                       void **     info); /* Callback to deserialize a string into connector's info */
} H5VL_info_class_t;

/* VOL object wrap / retrieval callbacks */
/* (These only need to be implemented by "pass through" VOL connectors) */
typedef struct H5VL_wrap_class_t {
    void *(*get_object)(const void *obj); /* Callback to retrieve underlying object       */
    herr_t (*get_wrap_ctx)(
        const void *obj,
        void **     wrap_ctx); /* Callback to retrieve the object wrapping context for the connector */
    void *(*wrap_object)(void *obj, H5I_type_t obj_type,
                         void *wrap_ctx); /* Callback to wrap a library object */
    void *(*unwrap_object)(void *obj);    /* Callback to unwrap a library object */
    herr_t (*free_wrap_ctx)(
        void *wrap_ctx); /* Callback to release the object wrapping context for the connector */
} H5VL_wrap_class_t;

/* H5A routines */
typedef struct H5VL_attr_class_t {
    void *(*create)(void *obj, const H5VL_loc_params_t *loc_params, const char *attr_name, hid_t type_id,
                    hid_t space_id, hid_t acpl_id, hid_t aapl_id, hid_t dxpl_id, void **req);
    void *(*open)(void *obj, const H5VL_loc_params_t *loc_params, const char *attr_name, hid_t aapl_id,
                  hid_t dxpl_id, void **req);
    herr_t (*read)(void *attr, hid_t mem_type_id, void *buf, hid_t dxpl_id, void **req);
    herr_t (*write)(void *attr, hid_t mem_type_id, const void *buf, hid_t dxpl_id, void **req);
    herr_t (*get)(void *obj, H5VL_attr_get_t get_type, hid_t dxpl_id, void **req, va_list arguments);
    herr_t (*specific)(void *obj, const H5VL_loc_params_t *loc_params, H5VL_attr_specific_t specific_type,
                       hid_t dxpl_id, void **req, va_list arguments);
    herr_t (*optional)(void *obj, H5VL_attr_optional_t opt_type, hid_t dxpl_id, void **req,
                       va_list arguments);
    herr_t (*close)(void *attr, hid_t dxpl_id, void **req);
} H5VL_attr_class_t;

/* H5D routines */
typedef struct H5VL_dataset_class_t {
    void *(*create)(void *obj, const H5VL_loc_params_t *loc_params, const char *name, hid_t lcpl_id,
                    hid_t type_id, hid_t space_id, hid_t dcpl_id, hid_t dapl_id, hid_t dxpl_id, void **req);
    void *(*open)(void *obj, const H5VL_loc_params_t *loc_params, const char *name, hid_t dapl_id,
                  hid_t dxpl_id, void **req);
    herr_t (*read)(void *dset, hid_t mem_type_id, hid_t mem_space_id, hid_t file_space_id, hid_t dxpl_id,
                   void *buf, void **req);
    herr_t (*write)(void *dset, hid_t mem_type_id, hid_t mem_space_id, hid_t file_space_id, hid_t dxpl_id,
                    const void *buf, void **req);
    herr_t (*get)(void *obj, H5VL_dataset_get_t get_type, hid_t dxpl_id, void **req, va_list arguments);
    herr_t (*specific)(void *obj, H5VL_dataset_specific_t specific_type, hid_t dxpl_id, void **req,
                       va_list arguments);
    herr_t (*optional)(void *obj, H5VL_dataset_optional_t opt_type, hid_t dxpl_id, void **req,
                       va_list arguments);
    herr_t (*close)(void *dset, hid_t dxpl_id, void **req);
} H5VL_dataset_class_t;

/* H5T routines*/
typedef struct H5VL_datatype_class_t {
    void *(*commit)(void *obj, const H5VL_loc_params_t *loc_params, const char *name, hid_t type_id,
                    hid_t lcpl_id, hid_t tcpl_id, hid_t tapl_id, hid_t dxpl_id, void **req);
    void *(*open)(void *obj, const H5VL_loc_params_t *loc_params, const char *name, hid_t tapl_id,
                  hid_t dxpl_id, void **req);
    herr_t (*get)(void *obj, H5VL_datatype_get_t get_type, hid_t dxpl_id, void **req, va_list arguments);
    herr_t (*specific)(void *obj, H5VL_datatype_specific_t specific_type, hid_t dxpl_id, void **req,
                       va_list arguments);
    herr_t (*optional)(void *obj, H5VL_datatype_optional_t opt_type, hid_t dxpl_id, void **req,
                       va_list arguments);
    herr_t (*close)(void *dt, hid_t dxpl_id, void **req);
} H5VL_datatype_class_t;

/* H5F routines */
typedef struct H5VL_file_class_t {
    void *(*create)(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id, hid_t dxpl_id,
                    void **req);
    void *(*open)(const char *name, unsigned flags, hid_t fapl_id, hid_t dxpl_id, void **req);
    herr_t (*get)(void *obj, H5VL_file_get_t get_type, hid_t dxpl_id, void **req, va_list arguments);
    herr_t (*specific)(void *obj, H5VL_file_specific_t specific_type, hid_t dxpl_id, void **req,
                       va_list arguments);
    herr_t (*optional)(void *obj, H5VL_file_optional_t opt_type, hid_t dxpl_id, void **req,
                       va_list arguments);
    herr_t (*close)(void *file, hid_t dxpl_id, void **req);
} H5VL_file_class_t;

/* H5G routines */
typedef struct H5VL_group_class_t {
    void *(*create)(void *obj, const H5VL_loc_params_t *loc_params, const char *name, hid_t lcpl_id,
                    hid_t gcpl_id, hid_t gapl_id, hid_t dxpl_id, void **req);
    void *(*open)(void *obj, const H5VL_loc_params_t *loc_params, const char *name, hid_t gapl_id,
                  hid_t dxpl_id, void **req);
    herr_t (*get)(void *obj, H5VL_group_get_t get_type, hid_t dxpl_id, void **req, va_list arguments);
    herr_t (*specific)(void *obj, H5VL_group_specific_t specific_type, hid_t dxpl_id, void **req,
                       va_list arguments);
    herr_t (*optional)(void *obj, H5VL_group_optional_t opt_type, hid_t dxpl_id, void **req,
                       va_list arguments);
    herr_t (*close)(void *grp, hid_t dxpl_id, void **req);
} H5VL_group_class_t;

/* H5L routines */
typedef struct H5VL_link_class_t {
    herr_t (*create)(H5VL_link_create_type_t create_type, void *obj, const H5VL_loc_params_t *loc_params,
                     hid_t lcpl_id, hid_t lapl_id, hid_t dxpl_id, void **req, va_list arguments);
    herr_t (*copy)(void *src_obj, const H5VL_loc_params_t *loc_params1, void *dst_obj,
                   const H5VL_loc_params_t *loc_params2, hid_t lcpl_id, hid_t lapl_id, hid_t dxpl_id,
                   void **req);
    herr_t (*move)(void *src_obj, const H5VL_loc_params_t *loc_params1, void *dst_obj,
                   const H5VL_loc_params_t *loc_params2, hid_t lcpl_id, hid_t lapl_id, hid_t dxpl_id,
                   void **req);
    herr_t (*get)(void *obj, const H5VL_loc_params_t *loc_params, H5VL_link_get_t get_type, hid_t dxpl_id,
                  void **req, va_list arguments);
    herr_t (*specific)(void *obj, const H5VL_loc_params_t *loc_params, H5VL_link_specific_t specific_type,
                       hid_t dxpl_id, void **req, va_list arguments);
    herr_t (*optional)(void *obj, H5VL_link_optional_t opt_type, hid_t dxpl_id, void **req,
                       va_list arguments);
} H5VL_link_class_t;

/* H5O routines */
typedef struct H5VL_object_class_t {
    void *(*open)(void *obj, const H5VL_loc_params_t *loc_params, H5I_type_t *opened_type, hid_t dxpl_id,
                  void **req);
    herr_t (*copy)(void *src_obj, const H5VL_loc_params_t *loc_params1, const char *src_name, void *dst_obj,
                   const H5VL_loc_params_t *loc_params2, const char *dst_name, hid_t ocpypl_id, hid_t lcpl_id,
                   hid_t dxpl_id, void **req);
    herr_t (*get)(void *obj, const H5VL_loc_params_t *loc_params, H5VL_object_get_t get_type, hid_t dxpl_id,
                  void **req, va_list arguments);
    herr_t (*specific)(void *obj, const H5VL_loc_params_t *loc_params, H5VL_object_specific_t specific_type,
                       hid_t dxpl_id, void **req, va_list arguments);
    herr_t (*optional)(void *obj, H5VL_object_optional_t opt_type, hid_t dxpl_id, void **req,
                       va_list arguments);
} H5VL_object_class_t;

/* Asynchronous request 'notify' callback */
typedef herr_t (*H5VL_request_notify_t)(void *ctx, H5ES_status_t status);

/* "Levels" for 'get connector class' introspection callback */
typedef enum H5VL_get_conn_lvl_t {
    H5VL_GET_CONN_LVL_CURR, /* Get "current" connector (for this object) */
    H5VL_GET_CONN_LVL_TERM  /* Get "terminal" connector (for this object) */
                            /* (Recursively called, for pass-through connectors) */
                            /* (Connectors that "split" must choose which connector to return) */
} H5VL_get_conn_lvl_t;

/* Forward declaration of H5VL_class_t, defined later in this file */
struct H5VL_class_t;

/* Container/connector introspection routines */
typedef struct H5VL_introspect_class_t {
    herr_t (*get_conn_cls)(void *obj, H5VL_get_conn_lvl_t lvl, const struct H5VL_class_t **conn_cls);
    herr_t (*opt_query)(void *obj, H5VL_subclass_t cls, int opt_type, hbool_t *supported);
} H5VL_introspect_class_t;

/* Async request operation routines */
typedef struct H5VL_request_class_t {
    herr_t (*wait)(void *req, uint64_t timeout, H5ES_status_t *status);
    herr_t (*notify)(void *req, H5VL_request_notify_t cb, void *ctx);
    herr_t (*cancel)(void *req);
    herr_t (*specific)(void *req, H5VL_request_specific_t specific_type, va_list arguments);
    herr_t (*optional)(void *req, H5VL_request_optional_t opt_type, va_list arguments);
    herr_t (*free)(void *req);
} H5VL_request_class_t;

/* 'blob' routines */
typedef struct H5VL_blob_class_t {
    herr_t (*put)(void *obj, const void *buf, size_t size, void *blob_id, void *ctx);
    herr_t (*get)(void *obj, const void *blob_id, void *buf, size_t size, void *ctx);
    herr_t (*specific)(void *obj, void *blob_id, H5VL_blob_specific_t specific_type, va_list arguments);
    herr_t (*optional)(void *obj, void *blob_id, H5VL_blob_optional_t opt_type, va_list arguments);
} H5VL_blob_class_t;

/* Object token routines */
typedef struct H5VL_token_class_t {
    herr_t (*cmp)(void *obj, const H5O_token_t *token1, const H5O_token_t *token2, int *cmp_value);
    herr_t (*to_str)(void *obj, H5I_type_t obj_type, const H5O_token_t *token, char **token_str);
    herr_t (*from_str)(void *obj, H5I_type_t obj_type, const char *token_str, H5O_token_t *token);
} H5VL_token_class_t;

/**
 * \ingroup H5VLDEV
 * Class information for each VOL connector
 */
//! [H5VL_class_t_snip]
typedef struct H5VL_class_t {
    /* Overall connector fields & callbacks */
    unsigned           version;          /**< VOL connector class struct version #     */
    H5VL_class_value_t value;            /**< Value to identify connector              */
    const char *       name;             /**< Connector name (MUST be unique!)         */
    unsigned           cap_flags;        /**< Capability flags for connector           */
    herr_t (*initialize)(hid_t vipl_id); /**< Connector initialization callback        */
    herr_t (*terminate)(void);           /**< Connector termination callback           */

    /* VOL framework */
    H5VL_info_class_t info_cls; /**< VOL info fields & callbacks  */
    H5VL_wrap_class_t wrap_cls; /**< VOL object wrap / retrieval callbacks */

    /* Data Model */
    H5VL_attr_class_t     attr_cls;     /**< Attribute (H5A*) class callbacks */
    H5VL_dataset_class_t  dataset_cls;  /**< Dataset (H5D*) class callbacks   */
    H5VL_datatype_class_t datatype_cls; /**< Datatype (H5T*) class callbacks  */
    H5VL_file_class_t     file_cls;     /**< File (H5F*) class callbacks      */
    H5VL_group_class_t    group_cls;    /**< Group (H5G*) class callbacks     */
    H5VL_link_class_t     link_cls;     /**< Link (H5L*) class callbacks      */
    H5VL_object_class_t   object_cls;   /**< Object (H5O*) class callbacks    */

    /* Infrastructure / Services */
    H5VL_introspect_class_t introspect_cls; /**< Container/connector introspection class callbacks */
    H5VL_request_class_t    request_cls;    /**< Asynchronous request class callbacks */
    H5VL_blob_class_t       blob_cls;       /**< 'Blob' class callbacks */
    H5VL_token_class_t      token_cls;      /**< VOL connector object token class callbacks */

    /* Catch-all */
    herr_t (*optional)(void *obj, int op_type, hid_t dxpl_id, void **req,
                       va_list arguments); /**< Optional callback */
} H5VL_class_t;
//! [H5VL_class_t_snip]

/********************/
/* Public Variables */
/********************/

/*********************/
/* Public Prototypes */
/*********************/

#ifdef __cplusplus
extern "C" {
#endif

/* Helper routines for VOL connector authors */
/**
 * \ingroup H5VLDEV
 * \brief Registers a new VOL connector
 *
 * \param[in] cls A pointer to the plugin structure to register
 * \vipl_id
 * \return \hid_t{VOL connector}
 *
 * \details H5VLregister_connector() registers a new VOL connector as a member
 *          of the virtual object layer class. This VOL connector identifier is
 *          good until the library is closed or the connector is unregistered.
 *
 *          \p vipl_id is either #H5P_DEFAULT or the identifier of a VOL
 *          initialization property list of class #H5P_VOL_INITIALIZE created
 *          with H5Pcreate(). When created, this property list contains no
 *          library properties. If a VOL connector author decides that
 *          initialization-specific data are needed, they can be added to the
 *          empty list and retrieved by the connector in the VOL connector's
 *          initialize callback. Use of the VOL initialization property list is
 *          uncommon, as most VOL-specific properties are added to the file
 *          access property list via the connector's API calls which set the
 *          VOL connector for the file open/create. For more information, see
 *          the VOL documentation.
 *
 *          H5VL_class_t is defined in H5VLconnector.h in the source code. It
 *          contains class information for each VOL connector:
 *          \snippet this H5VL_class_t_snip
 *
 * \todo Fix the reference to VOL documentation.
 *
 * \since 1.12.0
 */
H5_DLL hid_t H5VLregister_connector(const H5VL_class_t *cls, hid_t vipl_id);
/**
 * \ingroup H5VLDEV
 */
H5_DLL void *H5VLobject(hid_t obj_id);
/**
 * \ingroup H5VLDEV
 */
H5_DLL hid_t H5VLget_file_type(void *file_obj, hid_t connector_id, hid_t dtype_id);
/**
 * \ingroup H5VLDEV
 */
H5_DLL hid_t H5VLpeek_connector_id_by_name(const char *name);
/**
 * \ingroup H5VLDEV
 */
H5_DLL hid_t H5VLpeek_connector_id_by_value(H5VL_class_value_t value);

#ifdef __cplusplus
}
#endif

#endif /* _H5VLconnector_H */