__root_device_register(9)

💅 NAME 💅

okay so welcome to the __root_device_register(9) page from the Kernel API Manual 💖. This function is literally called __root_device_register and it does exactly one iconic thing: allocate and register a root device. Periodt.

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✨ SYNOPSIS ✨

struct device * __root_device_register (const char *name , struct module *owner );

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🎀 ARGUMENTS 🎀

• name — the root device name, bestie. That's the name.
• owner — owner module of the root device, usually THIS_MODULE.

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🦋 DESCRIPTION 🦋

So this function allocates a root device and registers it using device_register. The way that it works is very main-character: it gives you a struct device * back, and when you're done with it you free it with root_device_unregister. Don't forget, that's the freeing part 😭.

Root devices are dummy devices — yes, dummy devices — which allow other devices to be grouped under /sys/devices. Use this function to allocate a root device and then use it as the parent of any device which should appear under /sys/devices/{name}. Slay.

The /sys/devices/{name} directory will also contain a in sysfs. (That's exactly what the page says, no cap — don't ask me, I just work here 🙈.)

It returns a struct device pointer on success, or ERR_PTR on error. Keep that in mind for your vibe check.

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💀 NOTE 💀

You probably want to use root_device_register. Like... this one has the double underscore. Just saying. 💅

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🌈 SEE ALSO 🌈

Kernel file ./drivers/base/core.c — and the whole friend group is: __fwnode_link_add(9), __fwnode_link_del(9), __fwnode_link_cycle(9), fwnode_links_purge_suppliers(9), fwnode_links_purge_consumers(9), fwnode_links_purge(9), __fwnode_links_move_consumers(9), __fw_devlink_pickup_dangling_consumers(9), fw_devlink_refresh_fwnode(9), device_is_dependent(9), device_pm_move_to_tail(9), device_link_wait_removal(9), device_link_add(9), device_link_del(9), device_link_remove(9), device_links_check_suppliers(9), __device_links_queue_sync_state(9), device_links_flush_sync_list(9), device_links_force_bind(9), device_links_driver_bound(9), __device_links_no_driver(9), device_links_no_driver(9), device_links_driver_cleanup(9), device_links_busy(9), device_links_unbind_consumers(9), device_links_purge(9), wait_for_init_devices_probe(9), fwnode_is_ancestor_of(9), fwnode_get_next_parent_dev(9), __fw_devlink_relax_cycles(9), fw_devlink_create_devlink(9), __fw_devlink_link_to_consumers(9), __fw_devlink_link_to_suppliers(9), dev_driver_string(9), device_release(9), devm_device_add_group(9), devices_kset_move_before(9), devices_kset_move_after(9), devices_kset_move_last(9), device_create_file(9), device_remove_file(9), device_remove_file_self(9), device_create_bin_file(9), device_remove_bin_file(9), device_initialize(9), kobject_has_children(9), dev_set_name(9), device_add(9), device_register(9), get_device(9), put_device(9), device_del(9), device_unregister(9), device_get_devnode(9), device_for_each_child(9), device_for_each_child_reverse(9), device_for_each_child_reverse_from(9), device_find_child(9), device_offline(9), device_online(9), root_device_unregister(9), device_create(9), device_create_with_groups(9), device_destroy(9), device_rename(9), device_move(9), device_change_owner(9), device_shutdown(9), dev_err_probe(9), dev_warn_probe(9), set_primary_fwnode(9), set_secondary_fwnode(9), device_remove_of_node(9), device_add_of_node(9), device_set_of_node_from_dev(9), get_dev_from_fwnode(9).

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mwah 💋 this lil page lives in ./drivers/base, dated October 2026. Byeee 🫶