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  */
24 struct path_selector_type;
25 struct 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 */
45 struct 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 */
96 int dm_register_path_selector(struct path_selector_type *type);
97 
98 /* Unregister a path selector */
99 int dm_unregister_path_selector(struct path_selector_type *type);
100 
101 /* Returns a registered path selector type */
102 struct path_selector_type *dm_get_path_selector(const char *name);
103 
104 /* Releases a path selector  */
105 void dm_put_path_selector(struct path_selector_type *pst);
106 
107 #endif
108