// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright 2023 Red Hat
 */

#include "action-manager.h"

#include "memory-alloc.h"
#include "permassert.h"

#include "admin-state.h"
#include "completion.h"
#include "status-codes.h"
#include "types.h"
#include "vdo.h"

/**
 * struct action - An action to be performed in each of a set of zones.
 * @in_use: Whether this structure is in use.
 * @operation: The admin operation associated with this action.
 * @preamble: The method to run on the initiator thread before the action is applied to each zone.
 * @zone_action: The action to be performed in each zone.
 * @conclusion: The method to run on the initiator thread after the action is applied to each zone.
 * @parent: The object to notify when the action is complete.
 * @context: The action specific context.
 * @next: The action to perform after this one.
 */
struct action {
        bool in_use;
        const struct admin_state_code *operation;
        vdo_action_preamble_fn preamble;
        vdo_zone_action_fn zone_action;
        vdo_action_conclusion_fn conclusion;
        struct vdo_completion *parent;
        void *context;
        struct action *next;
};

/**
 * struct action_manager - Definition of an action manager.
 * @completion: The completion for performing actions.
 * @state: The state of this action manager.
 * @actions: The two action slots.
 * @current_action: The current action slot.
 * @zones: The number of zones in which an action is to be applied.
 * @scheduler: A function to schedule a default next action.
 * @get_zone_thread_id: A function to get the id of the thread on which to apply an action to a
 *                      zone.
 * @initiator_thread_id: The ID of the thread on which actions may be initiated.
 * @context: Opaque data associated with this action manager.
 * @acting_zone: The zone currently being acted upon.
 */
struct action_manager {
        struct vdo_completion completion;
        struct admin_state state;
        struct action actions[2];
        struct action *current_action;
        zone_count_t zones;
        vdo_action_scheduler_fn scheduler;
        vdo_zone_thread_getter_fn get_zone_thread_id;
        thread_id_t initiator_thread_id;
        void *context;
        zone_count_t acting_zone;
};

static inline struct action_manager *as_action_manager(struct vdo_completion *completion)
{
        vdo_assert_completion_type(completion, VDO_ACTION_COMPLETION);
        return container_of(completion, struct action_manager, completion);
}

/* Implements vdo_action_scheduler_fn. */
static bool no_default_action(void *context __always_unused)
{
        return false;
}

/* Implements vdo_action_preamble_fn. */
static void no_preamble(void *context __always_unused, struct vdo_completion *completion)
{
        vdo_finish_completion(completion);
}

/* Implements vdo_action_conclusion_fn. */
static int no_conclusion(void *context __always_unused)
{
        return VDO_SUCCESS;
}

/**
 * vdo_make_action_manager() - Make an action manager.
 * @zones: The number of zones to which actions will be applied.
 * @get_zone_thread_id: A function to get the thread id associated with a zone.
 * @initiator_thread_id: The thread on which actions may initiated.
 * @context: The object which holds the per-zone context for the action.
 * @scheduler: A function to schedule a next action after an action concludes if there is no
 *             pending action (may be NULL).
 * @vdo: The vdo used to initialize completions.
 * @manager_ptr: A pointer to hold the new action manager.
 *
 * Return: VDO_SUCCESS or an error code.
 */
int vdo_make_action_manager(zone_count_t zones,
                            vdo_zone_thread_getter_fn get_zone_thread_id,
                            thread_id_t initiator_thread_id, void *context,
                            vdo_action_scheduler_fn scheduler, struct vdo *vdo,
                            struct action_manager **manager_ptr)
{
        struct action_manager *manager;
        int result = vdo_allocate(1, struct action_manager, __func__, &manager);

        if (result != VDO_SUCCESS)
                return result;

        *manager = (struct action_manager) {
                .zones = zones,
                .scheduler =
                        ((scheduler == NULL) ? no_default_action : scheduler),
                .get_zone_thread_id = get_zone_thread_id,
                .initiator_thread_id = initiator_thread_id,
                .context = context,
        };

        manager->actions[0].next = &manager->actions[1];
        manager->current_action = manager->actions[1].next =
                &manager->actions[0];
        vdo_set_admin_state_code(&manager->state, VDO_ADMIN_STATE_NORMAL_OPERATION);
        vdo_initialize_completion(&manager->completion, vdo, VDO_ACTION_COMPLETION);
        *manager_ptr = manager;
        return VDO_SUCCESS;
}

const struct admin_state_code *vdo_get_current_manager_operation(struct action_manager *manager)
{
        return vdo_get_admin_state_code(&manager->state);
}

void *vdo_get_current_action_context(struct action_manager *manager)
{
        return manager->current_action->in_use ? manager->current_action->context : NULL;
}

static void finish_action_callback(struct vdo_completion *completion);
static void apply_to_zone(struct vdo_completion *completion);

static thread_id_t get_acting_zone_thread_id(struct action_manager *manager)
{
        return manager->get_zone_thread_id(manager->context, manager->acting_zone);
}

static void preserve_error(struct vdo_completion *completion)
{
        if (completion->parent != NULL)
                vdo_set_completion_result(completion->parent, completion->result);

        vdo_reset_completion(completion);
        vdo_run_completion(completion);
}

static void prepare_for_next_zone(struct action_manager *manager)
{
        vdo_prepare_completion_for_requeue(&manager->completion, apply_to_zone,
                                           preserve_error,
                                           get_acting_zone_thread_id(manager),
                                           manager->current_action->parent);
}

static void prepare_for_conclusion(struct action_manager *manager)
{
        vdo_prepare_completion_for_requeue(&manager->completion, finish_action_callback,
                                           preserve_error, manager->initiator_thread_id,
                                           manager->current_action->parent);
}

static void apply_to_zone(struct vdo_completion *completion)
{
        zone_count_t zone;
        struct action_manager *manager = as_action_manager(completion);

        VDO_ASSERT_LOG_ONLY((vdo_get_callback_thread_id() == get_acting_zone_thread_id(manager)),
                            "%s() called on acting zones's thread", __func__);

        zone = manager->acting_zone++;
        if (manager->acting_zone == manager->zones) {
                /*
                 * We are about to apply to the last zone. Once that is finished, we're done, so go
                 * back to the initiator thread and finish up.
                 */
                prepare_for_conclusion(manager);
        } else {
                /* Prepare to come back on the next zone */
                prepare_for_next_zone(manager);
        }

        manager->current_action->zone_action(manager->context, zone, completion);
}

static void handle_preamble_error(struct vdo_completion *completion)
{
        /* Skip the zone actions since the preamble failed. */
        completion->callback = finish_action_callback;
        preserve_error(completion);
}

static void launch_current_action(struct action_manager *manager)
{
        struct action *action = manager->current_action;
        int result = vdo_start_operation(&manager->state, action->operation);

        if (result != VDO_SUCCESS) {
                if (action->parent != NULL)
                        vdo_set_completion_result(action->parent, result);

                /* We aren't going to run the preamble, so don't run the conclusion */
                action->conclusion = no_conclusion;
                finish_action_callback(&manager->completion);
                return;
        }

        if (action->zone_action == NULL) {
                prepare_for_conclusion(manager);
        } else {
                manager->acting_zone = 0;
                vdo_prepare_completion_for_requeue(&manager->completion, apply_to_zone,
                                                   handle_preamble_error,
                                                   get_acting_zone_thread_id(manager),
                                                   manager->current_action->parent);
        }

        action->preamble(manager->context, &manager->completion);
}

/**
 * vdo_schedule_default_action() - Attempt to schedule the default action.
 * @manager: The action manager.
 *
 * If the manager is not operating normally, the action will not be scheduled.
 *
 * Return: true if an action was scheduled.
 */
bool vdo_schedule_default_action(struct action_manager *manager)
{
        /* Don't schedule a default action if we are operating or not in normal operation. */
        const struct admin_state_code *code = vdo_get_current_manager_operation(manager);

        return ((code == VDO_ADMIN_STATE_NORMAL_OPERATION) &&
                manager->scheduler(manager->context));
}

static void finish_action_callback(struct vdo_completion *completion)
{
        bool has_next_action;
        int result;
        struct action_manager *manager = as_action_manager(completion);
        struct action action = *(manager->current_action);

        manager->current_action->in_use = false;
        manager->current_action = manager->current_action->next;

        /*
         * We need to check this now to avoid use-after-free issues if running the conclusion or
         * notifying the parent results in the manager being freed.
         */
        has_next_action =
                (manager->current_action->in_use || vdo_schedule_default_action(manager));
        result = action.conclusion(manager->context);
        vdo_finish_operation(&manager->state, VDO_SUCCESS);
        if (action.parent != NULL)
                vdo_continue_completion(action.parent, result);

        if (has_next_action)
                launch_current_action(manager);
}

/**
 * vdo_schedule_action() - Schedule an action to be applied to all zones.
 * @manager: The action manager to schedule the action on.
 * @preamble: A method to be invoked on the initiator thread once this action is started but before
 *            applying to each zone; may be NULL.
 * @action: The action to apply to each zone; may be NULL.
 * @conclusion: A method to be invoked back on the initiator thread once the action has been
 *              applied to all zones; may be NULL.
 * @parent: The object to notify once the action is complete or if the action can not be scheduled;
 *          may be NULL.
 *
 * The action will be launched immediately if there is no current action, or as soon as the current
 * action completes. If there is already a pending action, this action will not be scheduled, and,
 * if it has a parent, that parent will be notified. At least one of the preamble, action, or
 * conclusion must not be NULL.
 *
 * Return: true if the action was scheduled.
 */
bool vdo_schedule_action(struct action_manager *manager, vdo_action_preamble_fn preamble,
                         vdo_zone_action_fn action, vdo_action_conclusion_fn conclusion,
                         struct vdo_completion *parent)
{
        return vdo_schedule_operation(manager, VDO_ADMIN_STATE_OPERATING, preamble,
                                      action, conclusion, parent);
}

/**
 * vdo_schedule_operation() - Schedule an operation to be applied to all zones.
 * @manager: The action manager to schedule the action on.
 * @operation: The operation this action will perform
 * @preamble: A method to be invoked on the initiator thread once this action is started but before
 *            applying to each zone; may be NULL.
 * @action: The action to apply to each zone; may be NULL.
 * @conclusion: A method to be invoked back on the initiator thread once the action has been
 *              applied to all zones; may be NULL.
 * @parent: The object to notify once the action is complete or if the action can not be scheduled;
 *          may be NULL.
 *
 * The operation's action will be launched immediately if there is no current action, or as soon as
 * the current action completes. If there is already a pending action, this operation will not be
 * scheduled, and, if it has a parent, that parent will be notified. At least one of the preamble,
 * action, or conclusion must not be NULL.
 *
 * Return: true if the action was scheduled.
 */
bool vdo_schedule_operation(struct action_manager *manager,
                            const struct admin_state_code *operation,
                            vdo_action_preamble_fn preamble, vdo_zone_action_fn action,
                            vdo_action_conclusion_fn conclusion,
                            struct vdo_completion *parent)
{
        return vdo_schedule_operation_with_context(manager, operation, preamble, action,
                                                   conclusion, NULL, parent);
}

/**
 * vdo_schedule_operation_with_context() - Schedule an operation on all zones.
 * @manager: The action manager to schedule the action on.
 * @operation: The operation this action will perform.
 * @preamble: A method to be invoked on the initiator thread once this action is started but before
 *            applying to each zone; may be NULL.
 * @action: The action to apply to each zone; may be NULL.
 * @conclusion: A method to be invoked back on the initiator thread once the action has been
 *              applied to all zones; may be NULL.
 * @context: An action-specific context which may be retrieved via
 *           vdo_get_current_action_context(); may be NULL.
 * @parent: The object to notify once the action is complete or if the action can not be scheduled;
 *          may be NULL.
 *
 * The operation's action will be launched immediately if there is no current action, or as soon as
 * the current action completes. If there is already a pending action, this operation will not be
 * scheduled, and, if it has a parent, that parent will be notified. At least one of the preamble,
 * action, or conclusion must not be NULL.
 *
 * Return: true if the action was scheduled
 */
bool vdo_schedule_operation_with_context(struct action_manager *manager,
                                         const struct admin_state_code *operation,
                                         vdo_action_preamble_fn preamble,
                                         vdo_zone_action_fn action,
                                         vdo_action_conclusion_fn conclusion,
                                         void *context, struct vdo_completion *parent)
{
        struct action *current_action;

        VDO_ASSERT_LOG_ONLY((vdo_get_callback_thread_id() == manager->initiator_thread_id),
                            "action initiated from correct thread");
        if (!manager->current_action->in_use) {
                current_action = manager->current_action;
        } else if (!manager->current_action->next->in_use) {
                current_action = manager->current_action->next;
        } else {
                if (parent != NULL)
                        vdo_continue_completion(parent, VDO_COMPONENT_BUSY);

                return false;
        }

        *current_action = (struct action) {
                .in_use = true,
                .operation = operation,
                .preamble = (preamble == NULL) ? no_preamble : preamble,
                .zone_action = action,
                .conclusion = (conclusion == NULL) ? no_conclusion : conclusion,
                .context = context,
                .parent = parent,
                .next = current_action->next,
        };

        if (current_action == manager->current_action)
                launch_current_action(manager);

        return true;
}