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 */
20 enum 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 */
29 struct 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 */
39 struct 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
151 struct 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 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
181 int dm_cache_policy_register(struct dm_cache_policy_type *type);
182 void dm_cache_policy_unregister(struct dm_cache_policy_type *type);
183
184 /*----------------------------------------------------------------*/
185
186 #endif /* DM_CACHE_POLICY_H */