H5VLblob_optional

herr_t H5VLblob_optional(void *  obj,  hid_t connector_id,  void *  blob_id,
       H5VL_optional_args_t args,  void * *  req)

Performs an optional operation on a blob through the VOL.

`obj`	Object containing blob
`connector_id`	VOL connector identifier
`blob_id`	Blob identifier
`args`	Optional operation arguments
`req`	Async request object (can be null)

Non-negative on success, negative on failure.