Device Driver Tutorial

Defining the Get Driver Information Entry Point

The getinfo(9E) routine takes a pointer to a device number and returns a pointer to a device information structure or returns a device instance number. The return value of the getinfo(9E) routine is DDI_SUCCESS or DDI_FAILURE. The pointer or instance number requested from the getinfo(9E) routine is returned through a pointer argument.

The getinfo(9E) routine takes four arguments. The first argument is a pointer to the dev_info structure for this driver. This dev_info structure argument is obsolete and is no longer used by the getinfo(9E) routine.

The second argument to the getinfo(9E) routine is a constant that specifies what information the getinfo(9E) routine must return. The value of this second argument is either DDI_INFO_DEVT2DEVINFO or DDI_INFO_DEVT2INSTANCE. The third argument to the getinfo(9E) routine is a pointer to a device number. The fourth argument is a pointer to the place where the getinfo(9E) routine must store the requested information. The information stored at this location depends on the value you passed in the second argument to the getinfo(9E) routine.

The following table describes the relationship between the second and fourth arguments to the getinfo(9E) routine.

Table 2–1 Get Driver Information Entry Point Arguments





Device number 

Device information structure pointer 


Device number 

Device instance number 

The following code is the dummy_getinfo() routine that you should enter into your dummy.c file. You can copy the name portion of this function definition directly from the declaration you entered in Declaring the Autoconfiguration Entry Points.

static int
dummy_getinfo(dev_info_t *dip, ddi_info_cmd_t cmd, void *arg, 
    void **resultp)
    cmn_err(CE_NOTE, "Inside dummy_getinfo");
    switch(cmd) {
        *resultp = dummy_dip;
        return DDI_SUCCESS;
        *resultp = 0;
        return DDI_SUCCESS;
        return DDI_FAILURE;

First, use cmn_err(9F) to write a message to the system log, as you did in your _init(9E) entry point. Then provide DDI_INFO_DEVT2DEVINFO behavior. A realistic driver would use arg to get the instance number of this device node. A realistic driver would then call the ddi_get_soft_state(9F) function and return the device information structure pointer from that state structure. This dummy driver supports only one instance and does not use a state structure. In the DDI_INFO_DEVT2DEVINFO code of this dummy_getinfo() routine, simply return the one device information structure pointer that the dummy_attach() routine saved.

Next, provide DDI_INFO_DEVT2INSTANCE behavior. Within the DDI_INFO_DEVT2INSTANCE code, simply return 0. This dummy driver supports only one instance. The instance number of that one instance is 0.