On Thu, May 15 2025, Pasha Tatashin wrote:
> Introduce the framework for kernel subsystems (e.g., KVM, IOMMU, device
> drivers) to register with LUO and participate in the live update process
> via callbacks.
>
> Subsystem Registration:
> - Defines struct liveupdate_subsystem in linux/liveupdate.h,
> which subsystems use to provide their name and optional callbacks
> (prepare, freeze, cancel, finish). The callbacks accept
> a u64 *data intended for passing state/handles.
> - Exports liveupdate_register_subsystem() and
> liveupdate_unregister_subsystem() API functions.
> - Adds drivers/misc/liveupdate/luo_subsystems.c to manage a list
> of registered subsystems.
> Registration/unregistration is restricted to
> specific LUO states (NORMAL/UPDATED).
>
> Callback Framework:
> - The main luo_core.c state transition functions
> now delegate to new luo_do_subsystems_*_calls() functions
> defined in luo_subsystems.c.
> - These new functions are intended to iterate through the registered
> subsystems and invoke their corresponding callbacks.
>
> FDT Integration:
> - Adds a /subsystems subnode within the main LUO FDT created in
> luo_core.c. This node has its own compatibility string
> (subsystems-v1).
> - luo_subsystems_fdt_setup() populates this node by adding a
> property for each registered subsystem, using the subsystem's
> name.
> Currently, these properties are initialized with a placeholder
> u64 value (0).
> - luo_subsystems_startup() is called from luo_core.c on boot to
> find and validate the /subsystems node in the FDT received via
> KHO. It panics if the node is missing or incompatible.
> - Adds a stub API function liveupdate_get_subsystem_data() intended
> for subsystems to retrieve their persisted u64 data from the FDT
> in the new kernel.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
[...]
> +/**
> + * liveupdate_unregister_subsystem - Unregister a kernel subsystem handler from
> + * LUO
> + * @h: Pointer to the same liveupdate_subsystem structure that was used during
> + * registration.
> + *
> + * Unregisters a previously registered subsystem handler. Typically called
> + * during module exit or subsystem teardown. LUO removes the structure from its
> + * internal list; the caller is responsible for any necessary memory cleanup
> + * of the structure itself.
> + *
> + * Return: 0 on success, negative error code otherwise.
> + * -EINVAL if h is NULL.
> + * -ENOENT if the specified handler @h is not found in the registration list.
> + * -EBUSY if LUO is not in the NORMAL state.
> + */
> +int liveupdate_unregister_subsystem(struct liveupdate_subsystem *h)
> +{
> + struct liveupdate_subsystem *iter;
> + bool found = false;
> + int ret = 0;
> +
> + luo_state_read_enter();
> + if (!liveupdate_state_normal() && !liveupdate_state_updated()) {
> + luo_state_read_exit();
> + return -EBUSY;
> + }
> +
> + mutex_lock(&luo_subsystem_list_mutex);
> + list_for_each_entry(iter, &luo_subsystems_list, list) {
> + if (iter == h) {
> + found = true;
Nit: you don't actually need the found variable. You can do the same
check that list_for_each_entry() uses, which is to call
list_entry_is_head().
> + break;
> + }
> + }
> +
> + if (found) {
> + list_del_init(&h->list);
> + } else {
> + pr_warn("Subsystem handler '%s' not found for unregistration.\n",
> + h->name);
> + ret = -ENOENT;
> + }
> +
> + mutex_unlock(&luo_subsystem_list_mutex);
> + luo_state_read_exit();
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(liveupdate_unregister_subsystem);
[...]
--
Regards,
Pratyush Yadav
