ktypes

kobjects are associated with a specific type, called a ktype. ktypes are represented by struct kobj_type and defined in <linux/kobject.h>:

struct kobj_type {
        void (*release)(struct kobject *);
        struct sysfs_ops        *sysfs_ops;
        struct attribute        **default_attrs;
};

ktypes have the simple job of describing default behavior for a family of kobjects. Instead of each kobject defining its own behavior, the behavior is stored in a ktype, and kobjects of the same "type" share the same behavior.

The release pointer points to the deconstructor called when a kobject's reference count reaches zero. This function is responsible for freeing any memory associated with this kobject and otherwise cleaning up.

The sysfs_ops variable points to a sysfs_ops structure. This structure describes the behavior of sysfs files on read and write. It's covered in more detail in the section "Adding Files to sysfs."

Finally, default_attrs points to an array of attribute structures. These structures define the default attributes associated with this kobject. Attributes represent properties related to a given object. If this kobject is exported to sysfs, the attributes are exported as files. The last entry in the array must be NULL.