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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/*
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/* FIXME: make it clear which methods are optional. Get debug policy to
17 * double check this at start.
18 */
19
20/*
21 * The cache policy makes the important decisions about which blocks get to
22 * live on the faster cache device.
23 *
24 * When the core target has to remap a bio it calls the 'map' method of the
25 * policy. This returns an instruction telling the core target what to do.
26 *
27 * POLICY_HIT:
28 * That block is in the cache. Remap to the cache and carry on.
29 *
30 * POLICY_MISS:
31 * This block is on the origin device. Remap and carry on.
32 *
33 * POLICY_NEW:
34 * This block is currently on the origin device, but the policy wants to
35 * move it. The core should:
36 *
37 * - hold any further io to this origin block
38 * - copy the origin to the given cache block
39 * - release all the held blocks
40 * - remap the original block to the cache
41 *
42 * POLICY_REPLACE:
43 * This block is currently on the origin device. The policy wants to
44 * move it to the cache, with the added complication that the destination
45 * cache block needs a writeback first. The core should:
46 *
47 * - hold any further io to this origin block
48 * - hold any further io to the origin block that's being written back
49 * - writeback
50 * - copy new block to cache
51 * - release held blocks
52 * - remap bio to cache and reissue.
53 *
54 * Should the core run into trouble while processing a POLICY_NEW or
55 * POLICY_REPLACE instruction it will roll back the policies mapping using
56 * remove_mapping() or force_mapping(). These methods must not fail. This
57 * approach avoids having transactional semantics in the policy (ie, the
58 * core informing the policy when a migration is complete), and hence makes
59 * it easier to write new policies.
60 *
61 * In general policy methods should never block, except in the case of the
62 * map function when can_migrate is set. So be careful to implement using
63 * bounded, preallocated memory.
64 */
65enum policy_operation {
66 POLICY_HIT,
67 POLICY_MISS,
68 POLICY_NEW,
69 POLICY_REPLACE
70};
71
72/*
73 * When issuing a POLICY_REPLACE the policy needs to make a callback to
74 * lock the block being demoted. This doesn't need to occur during a
75 * writeback operation since the block remains in the cache.
76 */
77struct policy_locker;
78typedef int (*policy_lock_fn)(struct policy_locker *l, dm_oblock_t oblock);
79
80struct policy_locker {
81 policy_lock_fn fn;
82};
83
84/*
85 * This is the instruction passed back to the core target.
86 */
87struct policy_result {
88 enum policy_operation op;
89 dm_oblock_t old_oblock; /* POLICY_REPLACE */
90 dm_cblock_t cblock; /* POLICY_HIT, POLICY_NEW, POLICY_REPLACE */
91};
92
93/*
94 * The cache policy object. Just a bunch of methods. It is envisaged that
95 * this structure will be embedded in a bigger, policy specific structure
96 * (ie. use container_of()).
97 */
98struct dm_cache_policy {
99
100 /*
101 * FIXME: make it clear which methods are optional, and which may
102 * block.
103 */
104
105 /*
106 * Destroys this object.
107 */
108 void (*destroy)(struct dm_cache_policy *p);
109
110 /*
111 * See large comment above.
112 *
113 * oblock - the origin block we're interested in.
114 *
115 * can_block - indicates whether the current thread is allowed to
116 * block. -EWOULDBLOCK returned if it can't and would.
117 *
118 * can_migrate - gives permission for POLICY_NEW or POLICY_REPLACE
119 * instructions. If denied and the policy would have
120 * returned one of these instructions it should
121 * return -EWOULDBLOCK.
122 *
123 * discarded_oblock - indicates whether the whole origin block is
124 * in a discarded state (FIXME: better to tell the
125 * policy about this sooner, so it can recycle that
126 * cache block if it wants.)
127 * bio - the bio that triggered this call.
128 * result - gets filled in with the instruction.
129 *
130 * May only return 0, or -EWOULDBLOCK (if !can_migrate)
131 */
132 int (*map)(struct dm_cache_policy *p, dm_oblock_t oblock,
133 bool can_block, bool can_migrate, bool discarded_oblock,
134 struct bio *bio, struct policy_locker *locker,
135 struct policy_result *result);
136
137 /*
138 * Sometimes we want to see if a block is in the cache, without
139 * triggering any update of stats. (ie. it's not a real hit).
140 *
141 * Must not block.
142 *
143 * Returns 0 if in cache, -ENOENT if not, < 0 for other errors
144 * (-EWOULDBLOCK would be typical).
145 */
146 int (*lookup)(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock);
147
148 void (*set_dirty)(struct dm_cache_policy *p, dm_oblock_t oblock);
149 void (*clear_dirty)(struct dm_cache_policy *p, dm_oblock_t oblock);
150
151 /*
152 * Called when a cache target is first created. Used to load a
153 * mapping from the metadata device into the policy.
154 */
155 int (*load_mapping)(struct dm_cache_policy *p, dm_oblock_t oblock,
156 dm_cblock_t cblock, uint32_t hint, bool hint_valid);
157
158 /*
159 * Gets the hint for a given cblock. Called in a single threaded
160 * context. So no locking required.
161 */
162 uint32_t (*get_hint)(struct dm_cache_policy *p, dm_cblock_t cblock);
163
164 /*
165 * Override functions used on the error paths of the core target.
166 * They must succeed.
167 */
168 void (*remove_mapping)(struct dm_cache_policy *p, dm_oblock_t oblock);
169 void (*force_mapping)(struct dm_cache_policy *p, dm_oblock_t current_oblock,
170 dm_oblock_t new_oblock);
171
172 /*
173 * This is called via the invalidate_cblocks message. It is
174 * possible the particular cblock has already been removed due to a
175 * write io in passthrough mode. In which case this should return
176 * -ENODATA.
177 */
178 int (*remove_cblock)(struct dm_cache_policy *p, dm_cblock_t cblock);
179
180 /*
181 * Provide a dirty block to be written back by the core target. If
182 * critical_only is set then the policy should only provide work if
183 * it urgently needs it.
184 *
185 * Returns:
186 *
187 * 0 and @cblock,@oblock: block to write back provided
188 *
189 * -ENODATA: no dirty blocks available
190 */
191 int (*writeback_work)(struct dm_cache_policy *p, dm_oblock_t *oblock, dm_cblock_t *cblock,
192 bool critical_only);
193
194 /*
195 * How full is the cache?
196 */
197 dm_cblock_t (*residency)(struct dm_cache_policy *p);
198
199 /*
200 * Because of where we sit in the block layer, we can be asked to
201 * map a lot of little bios that are all in the same block (no
202 * queue merging has occurred). To stop the policy being fooled by
203 * these, the core target sends regular tick() calls to the policy.
204 * The policy should only count an entry as hit once per tick.
205 */
206 void (*tick)(struct dm_cache_policy *p, bool can_block);
207
208 /*
209 * Configuration.
210 */
211 int (*emit_config_values)(struct dm_cache_policy *p, char *result,
212 unsigned maxlen, ssize_t *sz_ptr);
213 int (*set_config_value)(struct dm_cache_policy *p,
214 const char *key, const char *value);
215
216 /*
217 * Book keeping ptr for the policy register, not for general use.
218 */
219 void *private;
220};
221
222/*----------------------------------------------------------------*/
223
224/*
225 * We maintain a little register of the different policy types.
226 */
227#define CACHE_POLICY_NAME_SIZE 16
228#define CACHE_POLICY_VERSION_SIZE 3
229
230struct dm_cache_policy_type {
231 /* For use by the register code only. */
232 struct list_head list;
233
234 /*
235 * Policy writers should fill in these fields. The name field is
236 * what gets passed on the target line to select your policy.
237 */
238 char name[CACHE_POLICY_NAME_SIZE];
239 unsigned version[CACHE_POLICY_VERSION_SIZE];
240
241 /*
242 * For use by an alias dm_cache_policy_type to point to the
243 * real dm_cache_policy_type.
244 */
245 struct dm_cache_policy_type *real;
246
247 /*
248 * Policies may store a hint for each each cache block.
249 * Currently the size of this hint must be 0 or 4 bytes but we
250 * expect to relax this in future.
251 */
252 size_t hint_size;
253
254 struct module *owner;
255 struct dm_cache_policy *(*create)(dm_cblock_t cache_size,
256 sector_t origin_size,
257 sector_t block_size);
258};
259
260int dm_cache_policy_register(struct dm_cache_policy_type *type);
261void dm_cache_policy_unregister(struct dm_cache_policy_type *type);
262
263/*----------------------------------------------------------------*/
264
265#endif /* DM_CACHE_POLICY_H */