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.
In Example 4-1, 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).
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 */ }