linux/drivers/md/dm-path-selector.h

/* 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 { … };

/*
 * 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 …
#define dm_ps_use_hr_timer(type) …

/* Information about a path selector type */
struct path_selector_type { … };

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

/* Unregister a path selector */
int 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