1 /*
2  * Copyright (C) 2003 Sistina Software.
3  * Copyright (C) 2004 Red Hat, Inc. All rights reserved.
4  *
5  * Module Author: Heinz Mauelshagen
6  *
7  * This file is released under the GPL.
8  *
9  * Path-Selector registration.
10  */
11 
12 #ifndef	DM_PATH_SELECTOR_H
13 #define	DM_PATH_SELECTOR_H
14 
15 #include <linux/device-mapper.h>
16 
17 #include "dm-mpath.h"
18 
19 /*
20  * We provide an abstraction for the code that chooses which path
21  * to send some io down.
22  */
23 struct path_selector_type;
24 struct path_selector {
25 	struct path_selector_type *type;
26 	void *context;
27 };
28 
29 /*
30  * If a path selector uses this flag, a high resolution timer is used
31  * (via ktime_get_ns) to account for IO start time in BIO-based mpath.
32  * This improves performance of some path selectors (i.e. HST), in
33  * exchange for slightly higher overhead when submitting the BIO.
34  * The extra cost is usually offset by improved path selection for
35  * some benchmarks.
36  *
37  * This has no effect for request-based mpath, since it already uses a
38  * higher precision timer by default.
39  */
40 #define DM_PS_USE_HR_TIMER		0x00000001
41 #define dm_ps_use_hr_timer(type)	((type)->features & DM_PS_USE_HR_TIMER)
42 
43 /* Information about a path selector type */
44 struct path_selector_type {
45 	char *name;
46 	struct module *module;
47 
48 	unsigned int features;
49 	unsigned int table_args;
50 	unsigned int info_args;
51 
52 	/*
53 	 * Constructs a path selector object, takes custom arguments
54 	 */
55 	int (*create) (struct path_selector *ps, unsigned argc, char **argv);
56 	void (*destroy) (struct path_selector *ps);
57 
58 	/*
59 	 * Add an opaque path object, along with some selector specific
60 	 * path args (eg, path priority).
61 	 */
62 	int (*add_path) (struct path_selector *ps, struct dm_path *path,
63 			 int argc, char **argv, char **error);
64 
65 	/*
66 	 * Chooses a path for this io, if no paths are available then
67 	 * NULL will be returned.
68 	 */
69 	struct dm_path *(*select_path) (struct path_selector *ps,
70 					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