/* SPDX-License-Identifier: GPL-2.0-only */
/*
 * Copyright (C) 2003 Sistina Software.
 * Copyright (C) 2004 Red Hat, Inc. All rights reserved.
 *
 * Module Author: Heinz Mauelshagen
 *
 * This file is released under the GPL.
 *
 * Path-Selector registration.
 */

#ifndef DM_PATH_SELECTOR_H
#define DM_PATH_SELECTOR_H

#include <linux/device-mapper.h>

#include "dm-mpath.h"

/*
 * We provide an abstraction for the code that chooses which path
 * to send some io down.
 */
struct path_selector_type;
struct path_selector {
        struct path_selector_type *type;
        void *context;
};

/*
 * If a path selector uses this flag, a high resolution timer is used
 * (via ktime_get_ns) to account for IO start time in BIO-based mpath.
 * This improves performance of some path selectors (i.e. HST), in
 * exchange for slightly higher overhead when submitting the BIO.
 * The extra cost is usually offset by improved path selection for
 * some benchmarks.
 *
 * This has no effect for request-based mpath, since it already uses a
 * higher precision timer by default.
 */
#define DM_PS_USE_HR_TIMER              0x00000001
#define dm_ps_use_hr_timer(type)        ((type)->features & DM_PS_USE_HR_TIMER)

/* Information about a path selector type */
struct path_selector_type {
        char *name;
        struct module *module;

        unsigned int features;
        unsigned int table_args;
        unsigned int info_args;

        /*
         * Constructs a path selector object, takes custom arguments
         */
        int (*create)(struct path_selector *ps, unsigned int argc, char **argv);
        void (*destroy)(struct path_selector *ps);

        /*
         * Add an opaque path object, along with some selector specific
         * path args (eg, path priority).
         */
        int (*add_path)(struct path_selector *ps, struct dm_path *path,
                        int argc, char **argv, char **error);

        /*
         * Chooses a path for this io, if no paths are available then
         * NULL will be returned.
         */
        struct dm_path *(*select_path)(struct path_selector *ps, size_t nr_bytes);

        /*
         * Notify the selector that a path has failed.
         */
        void (*fail_path)(struct path_selector *ps, struct dm_path *p);

        /*
         * Ask selector to reinstate a path.
         */
        int (*reinstate_path)(struct path_selector *ps, struct dm_path *p);

        /*
         * Table content based on parameters added in ps_add_path_fn
         * or path selector status
         */
        int (*status)(struct path_selector *ps, struct dm_path *path,
                      status_type_t type, char *result, unsigned int maxlen);

        int (*start_io)(struct path_selector *ps, struct dm_path *path,
                        size_t nr_bytes);
        int (*end_io)(struct path_selector *ps, struct dm_path *path,
                      size_t nr_bytes, u64 start_time);
};

/* Register a path selector */
int dm_register_path_selector(struct path_selector_type *type);

/* Unregister a path selector */
void dm_unregister_path_selector(struct path_selector_type *type);

/* Returns a registered path selector type */
struct path_selector_type *dm_get_path_selector(const char *name);

/* Releases a path selector  */
void dm_put_path_selector(struct path_selector_type *pst);

#endif