Attaching and Detaching

The attach(9E) entry point first calls the ddi_get_instance(9F) function to retrieve the instance number of the device information node. The attach(9E) entry point uses this instance number to call the ddi_soft_state_zalloc(9F), ddi_get_soft_state(9F), and ddi_create_minor_node(9F) functions.

The attach(9E) entry point calls the ddi_soft_state_zalloc(9F) function to create a state structure for this device instance. If creation of the soft state structure fails, attach(9E) writes an error message to a system log and returns failure. This device instance is not attached. If creation of the soft state structure succeeds, attach(9E) calls the ddi_get_soft_state(9F) function to retrieve the state structure for this device instance.

If retrieval of the state structure fails, attach(9E) writes an error message to a system log, calls the ddi_soft_state_free(9F) function to destroy the state structure that was created by ddi_soft_state_zalloc(9F), and returns failure. This device instance is not attached. If retrieval of the state structure succeeds, attach(9E) calls the ddi_create_minor_node(9F) function to create the device node.

At the top of this driver source file, a constant named QOTD_NAME is defined that holds the string name of the device. This constant is one of the arguments that is passed to ddi_create_minor_node(9F). If creation of the device node fails, attach(9E) writes an error message to a system log, calls the ddi_soft_state_free(9F) function to destroy the state structure that was created by ddi_soft_state_zalloc(9F), calls the ddi_remove_minor_node(9F) function, and returns failure. This device instance is not attached.

If creation of the device node succeeds, this device instance is attached. The attach(9E) entry point assigns the instance number that was retrieved with ddi_get_instance(9F) to the instance member of the state structure for this instance. Then attach(9E) assigns the dev_info structure pointer that was passed in the attach(9E) call to the dev_info structure pointer member of the state structure for this instance. The ddi_report_dev(9F) function writes a message in the system log file when the device is added or when the system is booted. The message announces this device as shown in the following example:

% dmesg
date time machine pseudo: [ID 129642 kern.info] pseudo-device: qotd_20
date time machine genunix: [ID 936769 kern.info] qotd_20 is /pseudo/qotd_2@0

The detach(9E) entry point first calls the ddi_get_instance(9F) function to retrieve the instance number of the device information node. The detach(9E) entry point uses this instance number to call the ddi_soft_state_free(9F) function to destroy the state structure that was created by ddi_soft_state_zalloc(9F) in the attach(9E) entry point. The detach(9E) entry point then calls the ddi_remove_minor_node(9F) function to remove the device that was created by ddi_create_minor_node(9F) in the attach(9E) entry point.