kobject

A kobject is the fundamental building block of the Linux kernel's object model used for representing kernel objects in sysfs. It is a lightweight, reference-counted container that participates in a hierarchical tree under the /sys pseudo-filesystem. Each kobject carries a name and may have a parent; it is associated with a kset (a group of related objects) and a kobj_type that describes its attributes and behavior.

The kobject hierarchy reflects kernel subsystems and devices. The parent pointer forms the tree; kset groups organize related objects; kobj_type describes the object's attribute set and lifecycle hooks. When a kobject is added to the sysfs tree, corresponding directories are created and files representing the object's attributes are created from the defined kobj_attributes and attribute groups.

Lifetime management is based on reference counting. Users can increase or decrease the reference count via kobject_get and kobject_put. When the last reference is released, a release callback is invoked, allowing the subsystem to free resources and remove any associated sysfs entries.

Attributes and sysfs integration are achieved by declaring attributes with kobj_attribute structures and grouping them into attribute groups. The sysfs interface exposes these attributes as files, enabling runtime inspection and control without requiring a reboot or recompilation.

Usage-wise, kobjects are widely used by drivers and kernel subsystems to expose information and controls. A driver typically creates a kobject for a device or subsystem, binds it into the appropriate part of the hierarchy, and defines attributes that appear under the /sys hierarchy, facilitating user-space interaction and debugging.