comedi_get_cmd_src_mask man page
comedi_get_cmd_src_mask — streaming input/output capabilities
int comedi_get_cmd_src_mask (comedi_t * device, unsigned int subdevice, comedi_cmd * command);
The command capabilities of the subdevice indicated by the parameters device and subdevice are probed, and the results placed in the command structure pointed to by the parameter command. The trigger source elements of the command structure are set to the logical OR value of possible trigger sources. Other elements in the structure are undefined. If sucessful, 0 is returned, otherwise -1.