The minidriver handler function

For this sample driver, the source code for the handler function looks like this:

struct mini_data
{
   uint16_t	nstartup;
   uint16_t	nstartupp;
   uint16_t	nstartupf;
   uint16_t	nkernel;
   uint16_t	nprocess;
   uint16_t	data_len;
};

/*
 * Sample minidriver handler function for debug purposes
 * 
 * Counts the number of calls for each state and
 * fills the data area with the current handler state
 */
int 
mini_data(int state, void *data)
{
   uint8_t		*dptr;
   struct mini_data	*mdata;
		
   mdata = (struct mini_data *) data;
   dptr = (uint8_t *) (mdata + 1);
	
   /* on MDRIVER_INIT, set up the data area */
   if (state == MDRIVER_INIT)
   {
      mdata->nstartup = 0;
      mdata->nstartupf = 0;
      mdata->nstartupp = 0;
      mdata->nkernel = 0;
      mdata->nprocess = 0;
      mdata->data_len = 0;
   }
	
   /* count the number of calls we get for each type */	
   if (state == MDRIVER_STARTUP)
      mdata->nstartup = mdata->nstartup + 1;
   else if (state == MDRIVER_STARTUP_PREPARE)
      mdata->nstartupp = mdata->nstartupp + 1;
   else if (state == MDRIVER_STARTUP_FINI)
      mdata->nstartupf = mdata->nstartupf + 1;
   else if (state == MDRIVER_KERNEL)
      mdata->nkernel = mdata->nkernel + 1;
   else if (state == MDRIVER_PROCESS)
      mdata->nprocess = mdata->nprocess + 1;
   else if (state == MDRIVER_INTR_ATTACH)
   {
      /* normally disable my interrupt */
      return (1);
   }
	
   /* put the state information in the data area 
   after the structure if we have room */
		
   if (mdata->data_len < 60000 ) {
      dptr[mdata->data_len] = (uint8_t) state;
      mdata->data_len = mdata->data_len + 1;
   }
		
   return (0);
}

A few things to note:

• The handler function stores call information, so a structure has been created to allow easier access to the data area.
• When the state is MDRIVER_INIT, the handler initializes the data area. The handler is called only once with this state.
• Before we store the state information, we make sure that we're not about to write outside the data area, lest we crash the startup.
• If the handler is called with MDRIVER_INTR_ATTACH, it returns a value of 1, requesting that the kernel remove the minidriver. However, due to the asynchronous nature of the system, there might be several more invocations of the handler after it has indicated that it wants to stop.