_bstr_hndl
int (*bstr_read)(struct _bstr_hndl *h, uchar_t *buf, off_t size);
int (*bstr_write)(struct _bstr_hndl *h, uchar_t *buf, off_t size);
int (*bstr_close)(struct _bstr_hndl *h);
int (*bstr_size)(struct _bstr_hndl *h, off_t *size);
void (*bstr_rewind)(struct _bstr_hndl *h);
typedef struct _bstr_hndl *bstreamhandle;