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 Mauelshagen
7 *
8 * This file is released under the GPL.
9 *
10 * Path-Selector registration.
11 */
12
13#ifndef DM_PATH_SELECTOR_H
14#define DM_PATH_SELECTOR_H
15
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 path
22 * 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 used
32 * (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), in
34 * exchange for slightly higher overhead when submitting the BIO.
35 * The extra cost is usually offset by improved path selection for
36 * some benchmarks.
37 *
38 * This has no effect for request-based mpath, since it already uses a
39 * higher precision timer by default.
40 */
41#define DM_PS_USE_HR_TIMER 0x00000001
42#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 arguments
55 */
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 specific
61 * 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 then
68 * 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_fn
84 * or path selector status
85 */
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 */
99void 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#endif
108

source code of linux/drivers/md/dm-path-selector.h