port_call flags?

[Vance Shipley]

The driver callback call() has a "flags" field which is undocumented.
The erl_driver.h header file includes a define which suggests it's use:

/* Constants for return flags from the 'port_call' callback */
#define DRIVER_CALL_KEEP_BUFFER 0x1

Can anyone provide me some insight about this?


	-Vance


int call(ErlDrvData drv_data, unsigned int command,
	char *buf, int len, char **rbuf, int rlen,
	unsigned int *flags)