comedi_lock man page
comedi_lock — subdevice reservation
int comedi_lock (comedi_t * device, unsigned int subdevice);
The function comedi_lock() reserves a subdevice for use by the current process. While the lock is held, no other process is allowed to read, write, or configure that subdevice, although other processes can read information about the subdevice. The lock is released when comedi_unlock() is called, or the device is closed.
If sucessful, 0 is returned. If there is an error, -1 is returned.