getinfo() Entry Point

The system calls getinfo(9E) to obtain configuration information that only the driver knows. The mapping of minor numbers to device instances is entirely under the control of the driver. The system sometimes needs to ask the driver which device a particular dev_t represents.

The getinfo() function can take either DDI_INFO_DEVT2INSTANCE or DDI_INFO_DEVT2DEVINFO as its infocmd argument. The DDI_INFO_DEVT2INSTANCE command requests the instance number of a device. The DDI_INFO_DEVT2DEVINFO command requests a pointer to the dev_info structure of a device.

In the DDI_INFO_DEVT2INSTANCE case, arg is a dev_t, and getinfo() must translate the minor number in dev_t to an instance number. In the following example, the minor number is the instance number, so getinfo() simply passes back the minor number. In this case, the driver must not assume that a state structure is available, since getinfo() might be called before attach(). The mapping defined by the driver between the minor device number and the instance number does not necessarily follow the mapping shown in the example. In all cases, however, the mapping must be static.

In the DDI_INFO_DEVT2DEVINFO case, arg is again a dev_t, so getinfo() first decodes the instance number for the device. getinfo() then passes back the dev_info pointer saved in the driver's soft state structure for the appropriate device, as shown in the following example.

Example 6–7 Typical getinfo() Entry Point

/*
 * getinfo(9e)
 * Return the instance number or device node given a dev_t
 */
static int
xxgetinfo(dev_info_t *dip, ddi_info_cmd_t infocmd, void *arg, void **result)
{
    int error;
    Pio *pio_p;
    int instance = getminor((dev_t)arg);

    switch (infocmd) {
    /*
     * return the device node if the driver has attached the
     * device instance identified by the dev_t value which was passed
     */
    case DDI_INFO_DEVT2DEVINFO:
    pio_p = ddi_get_soft_state(pio_softstate, instance);
    if (pio_p == NULL) {
        *result = NULL;
        error = DDI_FAILURE;
    } else {
        mutex_enter(&pio_p->mutex);
        *result = pio_p->dip;
        mutex_exit(&pio_p->mutex);
        error = DDI_SUCCESS;
    }
    break;
    /*
     * the driver can always return the instance number given a dev_t
     * value, even if the instance is not attached.
     */
    case DDI_INFO_DEVT2INSTANCE:
    *result = (void *)instance;
    error = DDI_SUCCESS;
    break;
    default:
    *result = NULL;
    error = DDI_FAILURE;
    }
    return (error);
}

The getinfo() routine must be kept in sync with the minor nodes that the driver creates. If the minor nodes get out of sync, any hotplug operations might fail and cause a system panic.