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1/*
2 * Copyright (C) 2012 Red Hat. All rights reserved.
3 *
4 * This file is released under the GPL.
5 */
6
7#ifndef DM_CACHE_POLICY_H
8#define DM_CACHE_POLICY_H
9
10#include "dm-cache-block-types.h"
11
12#include <linux/device-mapper.h>
13
14/*----------------------------------------------------------------*/
15
16/*
17 * The cache policy makes the important decisions about which blocks get to
18 * live on the faster cache device.
19 */
20enum policy_operation {
21 POLICY_PROMOTE,
22 POLICY_DEMOTE,
23 POLICY_WRITEBACK
24};
25
26/*
27 * This is the instruction passed back to the core target.
28 */
29struct policy_work {
30 enum policy_operation op;
31 dm_oblock_t oblock;
32 dm_cblock_t cblock;
33};
34
35/*
36 * The cache policy object. It is envisaged that this structure will be
37 * embedded in a bigger, policy specific structure (ie. use container_of()).
38 */
39struct dm_cache_policy {
40 /*
41 * Destroys this object.
42 */
43 void (*destroy)(struct dm_cache_policy *p);
44
45 /*
46 * Find the location of a block.
47 *
48 * Must not block.
49 *
50 * Returns 0 if in cache (cblock will be set), -ENOENT if not, < 0 for
51 * other errors (-EWOULDBLOCK would be typical). data_dir should be
52 * READ or WRITE. fast_copy should be set if migrating this block would
53 * be 'cheap' somehow (eg, discarded data). background_queued will be set
54 * if a migration has just been queued.
55 */
56 int (*lookup)(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock,
57 int data_dir, bool fast_copy, bool *background_queued);
58
59 /*
60 * Sometimes the core target can optimise a migration, eg, the
61 * block may be discarded, or the bio may cover an entire block.
62 * In order to optimise it needs the migration immediately though
63 * so it knows to do something different with the bio.
64 *
65 * This method is optional (policy-internal will fallback to using
66 * lookup).
67 */
68 int (*lookup_with_work)(struct dm_cache_policy *p,
69 dm_oblock_t oblock, dm_cblock_t *cblock,
70 int data_dir, bool fast_copy,
71 struct policy_work **work);
72
73 /*
74 * Retrieves background work. Returns -ENODATA when there's no
75 * background work.
76 */
77 int (*get_background_work)(struct dm_cache_policy *p, bool idle,
78 struct policy_work **result);
79
80 /*
81 * You must pass in the same work pointer that you were given, not
82 * a copy.
83 */
84 void (*complete_background_work)(struct dm_cache_policy *p,
85 struct policy_work *work,
86 bool success);
87
88 void (*set_dirty)(struct dm_cache_policy *p, dm_cblock_t cblock);
89 void (*clear_dirty)(struct dm_cache_policy *p, dm_cblock_t cblock);
90
91 /*
92 * Called when a cache target is first created. Used to load a
93 * mapping from the metadata device into the policy.
94 */
95 int (*load_mapping)(struct dm_cache_policy *p, dm_oblock_t oblock,
96 dm_cblock_t cblock, bool dirty,
97 uint32_t hint, bool hint_valid);
98
99 /*
100 * Drops the mapping, irrespective of whether it's clean or dirty.
101 * Returns -ENODATA if cblock is not mapped.
102 */
103 int (*invalidate_mapping)(struct dm_cache_policy *p, dm_cblock_t cblock);
104
105 /*
106 * Gets the hint for a given cblock. Called in a single threaded
107 * context. So no locking required.
108 */
109 uint32_t (*get_hint)(struct dm_cache_policy *p, dm_cblock_t cblock);
110
111 /*
112 * How full is the cache?
113 */
114 dm_cblock_t (*residency)(struct dm_cache_policy *p);
115
116 /*
117 * Because of where we sit in the block layer, we can be asked to
118 * map a lot of little bios that are all in the same block (no
119 * queue merging has occurred). To stop the policy being fooled by
120 * these, the core target sends regular tick() calls to the policy.
121 * The policy should only count an entry as hit once per tick.
122 *
123 * This method is optional.
124 */
125 void (*tick)(struct dm_cache_policy *p, bool can_block);
126
127 /*
128 * Configuration.
129 */
130 int (*emit_config_values)(struct dm_cache_policy *p, char *result,
131 unsigned maxlen, ssize_t *sz_ptr);
132 int (*set_config_value)(struct dm_cache_policy *p,
133 const char *key, const char *value);
134
135 void (*allow_migrations)(struct dm_cache_policy *p, bool allow);
136
137 /*
138 * Book keeping ptr for the policy register, not for general use.
139 */
140 void *private;
141};
142
143/*----------------------------------------------------------------*/
144
145/*
146 * We maintain a little register of the different policy types.
147 */
148#define CACHE_POLICY_NAME_SIZE 16
149#define CACHE_POLICY_VERSION_SIZE 3
150
151struct dm_cache_policy_type {
152 /* For use by the register code only. */
153 struct list_head list;
154
155 /*
156 * Policy writers should fill in these fields. The name field is
157 * what gets passed on the target line to select your policy.
158 */
159 char name[CACHE_POLICY_NAME_SIZE];
160 unsigned version[CACHE_POLICY_VERSION_SIZE];
161
162 /*
163 * For use by an alias dm_cache_policy_type to point to the
164 * real dm_cache_policy_type.
165 */
166 struct dm_cache_policy_type *real;
167
168 /*
169 * Policies may store a hint for each cache block.
170 * Currently the size of this hint must be 0 or 4 bytes but we
171 * expect to relax this in future.
172 */
173 size_t hint_size;
174
175 struct module *owner;
176 struct dm_cache_policy *(*create)(dm_cblock_t cache_size,
177 sector_t origin_size,
178 sector_t block_size);
179};
180
181int dm_cache_policy_register(struct dm_cache_policy_type *type);
182void dm_cache_policy_unregister(struct dm_cache_policy_type *type);
183
184/*----------------------------------------------------------------*/
185
186#endif /* DM_CACHE_POLICY_H */
1/* SPDX-License-Identifier: GPL-2.0-only */
2/*
3 * Copyright (C) 2012 Red Hat. All rights reserved.
4 *
5 * This file is released under the GPL.
6 */
7
8#ifndef DM_CACHE_POLICY_H
9#define DM_CACHE_POLICY_H
10
11#include "dm-cache-block-types.h"
12
13#include <linux/device-mapper.h>
14
15/*----------------------------------------------------------------*/
16
17/*
18 * The cache policy makes the important decisions about which blocks get to
19 * live on the faster cache device.
20 */
21enum policy_operation {
22 POLICY_PROMOTE,
23 POLICY_DEMOTE,
24 POLICY_WRITEBACK
25};
26
27/*
28 * This is the instruction passed back to the core target.
29 */
30struct policy_work {
31 enum policy_operation op;
32 dm_oblock_t oblock;
33 dm_cblock_t cblock;
34};
35
36/*
37 * The cache policy object. It is envisaged that this structure will be
38 * embedded in a bigger, policy specific structure (ie. use container_of()).
39 */
40struct dm_cache_policy {
41 /*
42 * Destroys this object.
43 */
44 void (*destroy)(struct dm_cache_policy *p);
45
46 /*
47 * Find the location of a block.
48 *
49 * Must not block.
50 *
51 * Returns 0 if in cache (cblock will be set), -ENOENT if not, < 0 for
52 * other errors (-EWOULDBLOCK would be typical). data_dir should be
53 * READ or WRITE. fast_copy should be set if migrating this block would
54 * be 'cheap' somehow (eg, discarded data). background_queued will be set
55 * if a migration has just been queued.
56 */
57 int (*lookup)(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock,
58 int data_dir, bool fast_copy, bool *background_queued);
59
60 /*
61 * Sometimes the core target can optimise a migration, eg, the
62 * block may be discarded, or the bio may cover an entire block.
63 * In order to optimise it needs the migration immediately though
64 * so it knows to do something different with the bio.
65 *
66 * This method is optional (policy-internal will fallback to using
67 * lookup).
68 */
69 int (*lookup_with_work)(struct dm_cache_policy *p,
70 dm_oblock_t oblock, dm_cblock_t *cblock,
71 int data_dir, bool fast_copy,
72 struct policy_work **work);
73
74 /*
75 * Retrieves background work. Returns -ENODATA when there's no
76 * background work.
77 */
78 int (*get_background_work)(struct dm_cache_policy *p, bool idle,
79 struct policy_work **result);
80
81 /*
82 * You must pass in the same work pointer that you were given, not
83 * a copy.
84 */
85 void (*complete_background_work)(struct dm_cache_policy *p,
86 struct policy_work *work,
87 bool success);
88
89 void (*set_dirty)(struct dm_cache_policy *p, dm_cblock_t cblock);
90 void (*clear_dirty)(struct dm_cache_policy *p, dm_cblock_t cblock);
91
92 /*
93 * Called when a cache target is first created. Used to load a
94 * mapping from the metadata device into the policy.
95 */
96 int (*load_mapping)(struct dm_cache_policy *p, dm_oblock_t oblock,
97 dm_cblock_t cblock, bool dirty,
98 uint32_t hint, bool hint_valid);
99
100 /*
101 * Drops the mapping, irrespective of whether it's clean or dirty.
102 * Returns -ENODATA if cblock is not mapped.
103 */
104 int (*invalidate_mapping)(struct dm_cache_policy *p, dm_cblock_t cblock);
105
106 /*
107 * Gets the hint for a given cblock. Called in a single threaded
108 * context. So no locking required.
109 */
110 uint32_t (*get_hint)(struct dm_cache_policy *p, dm_cblock_t cblock);
111
112 /*
113 * How full is the cache?
114 */
115 dm_cblock_t (*residency)(struct dm_cache_policy *p);
116
117 /*
118 * Because of where we sit in the block layer, we can be asked to
119 * map a lot of little bios that are all in the same block (no
120 * queue merging has occurred). To stop the policy being fooled by
121 * these, the core target sends regular tick() calls to the policy.
122 * The policy should only count an entry as hit once per tick.
123 *
124 * This method is optional.
125 */
126 void (*tick)(struct dm_cache_policy *p, bool can_block);
127
128 /*
129 * Configuration.
130 */
131 int (*emit_config_values)(struct dm_cache_policy *p, char *result,
132 unsigned int maxlen, ssize_t *sz_ptr);
133 int (*set_config_value)(struct dm_cache_policy *p,
134 const char *key, const char *value);
135
136 void (*allow_migrations)(struct dm_cache_policy *p, bool allow);
137
138 /*
139 * Book keeping ptr for the policy register, not for general use.
140 */
141 void *private;
142};
143
144/*----------------------------------------------------------------*/
145
146/*
147 * We maintain a little register of the different policy types.
148 */
149#define CACHE_POLICY_NAME_SIZE 16
150#define CACHE_POLICY_VERSION_SIZE 3
151
152struct dm_cache_policy_type {
153 /* For use by the register code only. */
154 struct list_head list;
155
156 /*
157 * Policy writers should fill in these fields. The name field is
158 * what gets passed on the target line to select your policy.
159 */
160 char name[CACHE_POLICY_NAME_SIZE];
161 unsigned int version[CACHE_POLICY_VERSION_SIZE];
162
163 /*
164 * For use by an alias dm_cache_policy_type to point to the
165 * real dm_cache_policy_type.
166 */
167 struct dm_cache_policy_type *real;
168
169 /*
170 * Policies may store a hint for each cache block.
171 * Currently the size of this hint must be 0 or 4 bytes but we
172 * expect to relax this in future.
173 */
174 size_t hint_size;
175
176 struct module *owner;
177 struct dm_cache_policy *(*create)(dm_cblock_t cache_size,
178 sector_t origin_size,
179 sector_t block_size);
180};
181
182int dm_cache_policy_register(struct dm_cache_policy_type *type);
183void dm_cache_policy_unregister(struct dm_cache_policy_type *type);
184
185/*----------------------------------------------------------------*/
186
187#endif /* DM_CACHE_POLICY_H */