prop_op(9E)

The prop_op(9E) entry point reports the values of device properties to the system. In many cases, the ddi_prop_op(9F) routine may be used as the driver's prop_op(9E) entry point in the cb_ops(9S) structure. ddi_prop_op(9F) performs all of the required processing and is sufficient for drivers that do not need to perform any special processing when handling a device property request.

However, there are cases when it is necessary for the driver to provide a prop_op(9E) entry point. For example, if a driver maintains a property whose value changes frequently, updating the property with ddi_prop_update(9F) each time it changes may not be efficient. Instead, the driver can maintain a local copy of the property in a C variable. The driver updates the C variable when the value of the property changes and does not call one of the ddi_prop_update(9F) routines. In this case, the prop_op(9E) entry point would need to intercept requests for this property and call one of the ddi_prop_update(9F) routines to update the value of the property before passing the request to ddi_prop_op(9F) to process the property request. See Example 3-4.

Here is the prop_op(9E) prototype:

int xxprop_op(dev_t dev, dev_info_t *dip,
 	ddi_prop_op_t  prop_op, int flags, char *name,
 	caddr_t valuep, int *lengthp);

Example 3-4 shows a simple implementation of the prop_op(9E) routine. This routine intercepts property requests and then uses the existing software property routines to update property values. For a complete description of all the parameters to (9E), see the manual page.

In Example 3-4, prop_op(9E) intercepts requests for the temperature property. The driver updates a variable in the state structure whenever the property changes but only updates the property when a request is made. It then uses the system routine ddi_prop_op(9F) to process the property request. If the property request is not specific to a device, the driver does not intercept the request. This is indicated when the value of the dev parameter is equal to DDI_DEV_T_ANY (the wildcard device number).

This example adds the following field to the state structure. See "Software State Structure" for more information.

	int		temperature; /* current device temperature */

Example 3-4 prop_op(9E) Routine

static int
xxprop_op(dev_t dev, dev_info_t *dip, ddi_prop_op_t prop_op,
	int flags, char *name, caddr_t valuep, int *lengthp)
{
	minor_t instance;
	struct xxstate *xsp;
	if (dev != DDI_DEV_T_ANY) {
			return (ddi_prop_op(dev, dip, prop_op, flags, name,
				valuep, lengthp));
	}

	instance = getminor(dev);
	xsp = ddi_get_soft_state(statep, instance);
	if (xsp == NULL)
			return (DDI_PROP_NOTFOUND);
	if (strcmp(name, "temperature") == 0) {
			ddi_prop_update_int(dev, dip, name, temperature);
	}

/* other cases */	
}