ctl function

The ctl function handles a driver-specific devctl() command. The prototype for this function is:

int ctl(
      void *hdl,
      int cmd,
      void *msg,
      int msglen,
      int *nbytes,
      int *info );

The arguments are:

hdl: The handle returned by the init function.
cmd: The device command.
msg: A pointer to the message buffer. The function can change the contents of the buffer.
msglen: The length of the message buffer, in bytes.
nbytes: The number of bytes being returned. This must not be greater than msglen.
info: A pointer to a location where the function can store extra status information returned by devctl().

The function must return: