VOL Developer

Detailed Description

Data Structures
struct	H5VL_class_t

Functions
hid_t	H5VLregister_connector (const H5VL_class_t *cls, hid_t vipl_id)
	Registers a new VOL connector.
void *	H5VLobject (hid_t obj_id)
hid_t	H5VLget_file_type (void *file_obj, hid_t connector_id, hid_t dtype_id)
herr_t	H5VLopen_lib_context (void **context)
	Opens a new internal context for the HDF5 library.
herr_t	H5VLclose_lib_context (void *context)
	Closes the internal state of the HDF5 library.

Function Documentation

H5VLclose_lib_context()

herr_t H5VLclose_lib_context

(

void *

context

)

Closes the internal state of the HDF5 library.

Parameters

[in]

context

library's context

Returns

Returns a non-negative value if successful; otherwise, returns a negative value.

Closes the internal state of the HDF5 library, undoing the effects of H5VLopen_lib_context(). This function must be called as a pair with H5VLopen_lib_context(). It can be invoked before, after, or independently of H5VLfree_lib_state().

Note

This routine is exclusively for authors of HDF5 VOL connectors. It is not part of the public HDF5 APIs for HDF5 application developers.

Since

2.0.0

H5VLget_file_type()

hid_t H5VLget_file_type	(	void *	file_obj,
		hid_t	connector_id,
		hid_t	dtype_id )

H5VLobject()

void * H5VLobject

(

hid_t

obj_id

)

H5VLopen_lib_context()

herr_t H5VLopen_lib_context

(

void **

context

)

Opens a new internal context for the HDF5 library.

Parameters

[out]

context

library's context

Returns

Returns a non-negative value if *context is set; otherwise returns negative value if *context is unset.

Opens a new internal context for the HDF5 library. The context returned (via the OUT parameter) must be passed to H5VLclose_lib_context() to conclude the library's context and release resources.

Note

This routine is exclusively for authors of HDF5 VOL connectors. It is not part of the public HDF5 APIs for HDF5 application developers.

Since

2.0.0

H5VLregister_connector()

hid_t H5VLregister_connector	(	const H5VL_class_t *	cls,
		hid_t	vipl_id )

Registers a new VOL connector.

Parameters

[in]	cls	A pointer to the plugin structure to register
[in]	vipl_id	VOL initialization property list identifier

Returns

Returns a VOL connector identifier if successful; otherwise returns H5I_INVALID_HID.

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.

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:

typedef struct H5VL_class_t {
    /* Overall connector fields & callbacks */
    unsigned           version;          
    H5VL_class_value_t value;            
    const char        *name;             
    unsigned           conn_version;     
    uint64_t           cap_flags;        
    herr_t (*initialize)(hid_t vipl_id); 
    herr_t (*terminate)(void);           
 
    /* VOL framework */
    H5VL_info_class_t info_cls; 
    H5VL_wrap_class_t wrap_cls; 
 
    /* Data Model */
    H5VL_attr_class_t     attr_cls;     
    H5VL_dataset_class_t  dataset_cls;  
    H5VL_datatype_class_t datatype_cls; 
    H5VL_file_class_t     file_cls;     
    H5VL_group_class_t    group_cls;    
    H5VL_link_class_t     link_cls;     
    H5VL_object_class_t   object_cls;   
 
    /* Infrastructure / Services */
    H5VL_introspect_class_t introspect_cls; 
    H5VL_request_class_t    request_cls;    
    H5VL_blob_class_t       blob_cls;       
    H5VL_token_class_t      token_cls;      
 
    /* Catch-all */
    herr_t (*optional)(void *obj, H5VL_optional_args_t *args, hid_t dxpl_id,
                       void **req); 
} H5VL_class_t;

Since

1.12.0