Device Driver Tutorial

Defining the Device Detach Entry Point

The detach(9E) routine takes two arguments. The first argument is a pointer to the dev_info structure for this driver. The second argument is a constant that specifies the detach type. The value that is passed through this second argument is either DDI_DETACH or DDI_SUSPEND. Every detach(9E) routine must define behavior for at least DDI_DETACH.

The DDI_DETACH code must undo everything that the DDI_ATTACH code did. In the DDI_ATTACH code in your attach(9E) routine, you saved the address of a new dev_info structure and you called the ddi_create_minor_node(9F) function to create a new node. In the DDI_DETACH code in this detach(9E) routine, you need to reset the variable that pointed to the dev_info structure for this node. You also need to call the ddi_remove_minor_node(9F) function to remove this node. The detach(9E) routine must deallocate anything that was allocated, close anything that was opened, and destroy anything that was created in the attach(9E) routine.

The following code is the dummy_detach() 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_detach(dev_info_t *dip, ddi_detach_cmd_t cmd)
    cmn_err(CE_NOTE, "Inside dummy_detach");
    switch(cmd) {
    case DDI_DETACH:
        dummy_dip = 0;
        ddi_remove_minor_node(dip, NULL);
        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_DETACH behavior. Within the DDI_DETACH code, first reset the dummy_dip variable that you set in dummy_attach() above. You cannot reset this device instance pointer unless you remove all instances of the device. This dummy driver supports only one instance.

Next, call the ddi_remove_minor_node(9F) function to remove this device node. The ddi_remove_minor_node(9F) function takes two arguments. The first argument is the device instance pointer that points to the dev_info structure of this device. The second argument is the name of the minor node you want to remove. If the value of the minor node argument is NULL, then ddi_remove_minor_node(9F) removes all instances of this device. Because the DDI_DETACH code of this driver always removes all instances, this dummy driver supports only one instance.

If the value of the cmd argument to this dummy_detach() routine is DDI_DETACH, remove all instances of this device and return DDI_SUCCESS. If this dummy_detach() routine receives any cmd other than DDI_DETACH, return DDI_FAILURE.