BIO Structure

struct bio_st
{
	BIO_METHOD *method;
	/* bio, mode, argp, argi, argl, ret */
	long (*callback)(struct bio_st *,int,const char *,int, long,long);
	char *cb_arg; /* first argument for the callback */
 
	int init;
	int shutdown;
	int flags;	/* extra storage */
 
	int retry_reason;
 
	int num;
	void *ptr;
	struct bio_st *next_bio;	/* used by filter BIOs */
	struct bio_st *prev_bio;	/* used by filter BIOs */
	int references;
	unsigned long num_read;
	unsigned long num_write;
 
	CRYPTO_EX_DATA ex_data;
};