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1/* SPDX-License-Identifier: GPL-2.0-only */2/*3 * Copyright (C) 2003 Sistina Software.4 * Copyright (C) 2004 Red Hat, Inc. All rights reserved.5 *6 * Module Author: Heinz Mauelshagen7 *8 * This file is released under the GPL.9 *10 * Path-Selector registration.11 */12 13#ifndef DM_PATH_SELECTOR_H14#define DM_PATH_SELECTOR_H15 16#include <linux/device-mapper.h>17 18#include "dm-mpath.h"19 20/*21 * We provide an abstraction for the code that chooses which path22 * to send some io down.23 */24struct path_selector_type;25struct path_selector {26 struct path_selector_type *type;27 void *context;28};29 30/*31 * If a path selector uses this flag, a high resolution timer is used32 * (via ktime_get_ns) to account for IO start time in BIO-based mpath.33 * This improves performance of some path selectors (i.e. HST), in34 * exchange for slightly higher overhead when submitting the BIO.35 * The extra cost is usually offset by improved path selection for36 * some benchmarks.37 *38 * This has no effect for request-based mpath, since it already uses a39 * higher precision timer by default.40 */41#define DM_PS_USE_HR_TIMER 0x0000000142#define dm_ps_use_hr_timer(type) ((type)->features & DM_PS_USE_HR_TIMER)43 44/* Information about a path selector type */45struct path_selector_type {46 char *name;47 struct module *module;48 49 unsigned int features;50 unsigned int table_args;51 unsigned int info_args;52 53 /*54 * Constructs a path selector object, takes custom arguments55 */56 int (*create)(struct path_selector *ps, unsigned int argc, char **argv);57 void (*destroy)(struct path_selector *ps);58 59 /*60 * Add an opaque path object, along with some selector specific61 * path args (eg, path priority).62 */63 int (*add_path)(struct path_selector *ps, struct dm_path *path,64 int argc, char **argv, char **error);65 66 /*67 * Chooses a path for this io, if no paths are available then68 * NULL will be returned.69 */70 struct dm_path *(*select_path)(struct path_selector *ps, size_t nr_bytes);71 72 /*73 * Notify the selector that a path has failed.74 */75 void (*fail_path)(struct path_selector *ps, struct dm_path *p);76 77 /*78 * Ask selector to reinstate a path.79 */80 int (*reinstate_path)(struct path_selector *ps, struct dm_path *p);81 82 /*83 * Table content based on parameters added in ps_add_path_fn84 * or path selector status85 */86 int (*status)(struct path_selector *ps, struct dm_path *path,87 status_type_t type, char *result, unsigned int maxlen);88 89 int (*start_io)(struct path_selector *ps, struct dm_path *path,90 size_t nr_bytes);91 int (*end_io)(struct path_selector *ps, struct dm_path *path,92 size_t nr_bytes, u64 start_time);93};94 95/* Register a path selector */96int dm_register_path_selector(struct path_selector_type *type);97 98/* Unregister a path selector */99int dm_unregister_path_selector(struct path_selector_type *type);100 101/* Returns a registered path selector type */102struct path_selector_type *dm_get_path_selector(const char *name);103 104/* Releases a path selector */105void dm_put_path_selector(struct path_selector_type *pst);106 107#endif108