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Joe Thornberc6b4fcb2013-03-01 22:45:51 +00001/*
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/*
Joe Thornberfb4100a2015-05-20 10:30:32 +010073 * 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/*
Joe Thornberc6b4fcb2013-03-01 22:45:51 +000085 * 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
93typedef int (*policy_walk_fn)(void *context, dm_cblock_t cblock,
94 dm_oblock_t oblock, uint32_t hint);
95
96/*
97 * The cache policy object. Just a bunch of methods. It is envisaged that
98 * this structure will be embedded in a bigger, policy specific structure
99 * (ie. use container_of()).
100 */
101struct dm_cache_policy {
102
103 /*
104 * FIXME: make it clear which methods are optional, and which may
105 * block.
106 */
107
108 /*
109 * Destroys this object.
110 */
111 void (*destroy)(struct dm_cache_policy *p);
112
113 /*
114 * See large comment above.
115 *
116 * oblock - the origin block we're interested in.
117 *
118 * can_block - indicates whether the current thread is allowed to
119 * block. -EWOULDBLOCK returned if it can't and would.
120 *
121 * can_migrate - gives permission for POLICY_NEW or POLICY_REPLACE
122 * instructions. If denied and the policy would have
123 * returned one of these instructions it should
124 * return -EWOULDBLOCK.
125 *
126 * discarded_oblock - indicates whether the whole origin block is
127 * in a discarded state (FIXME: better to tell the
128 * policy about this sooner, so it can recycle that
129 * cache block if it wants.)
130 * bio - the bio that triggered this call.
131 * result - gets filled in with the instruction.
132 *
133 * May only return 0, or -EWOULDBLOCK (if !can_migrate)
134 */
135 int (*map)(struct dm_cache_policy *p, dm_oblock_t oblock,
136 bool can_block, bool can_migrate, bool discarded_oblock,
Joe Thornberfb4100a2015-05-20 10:30:32 +0100137 struct bio *bio, struct policy_locker *locker,
138 struct policy_result *result);
Joe Thornberc6b4fcb2013-03-01 22:45:51 +0000139
140 /*
141 * Sometimes we want to see if a block is in the cache, without
142 * triggering any update of stats. (ie. it's not a real hit).
143 *
144 * Must not block.
145 *
Alasdair G Kergone12c1fd2013-05-10 14:37:17 +0100146 * Returns 0 if in cache, -ENOENT if not, < 0 for other errors
147 * (-EWOULDBLOCK would be typical).
Joe Thornberc6b4fcb2013-03-01 22:45:51 +0000148 */
149 int (*lookup)(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock);
150
Joe Thornberc6b4fcb2013-03-01 22:45:51 +0000151 void (*set_dirty)(struct dm_cache_policy *p, dm_oblock_t oblock);
152 void (*clear_dirty)(struct dm_cache_policy *p, dm_oblock_t oblock);
153
154 /*
155 * Called when a cache target is first created. Used to load a
156 * mapping from the metadata device into the policy.
157 */
158 int (*load_mapping)(struct dm_cache_policy *p, dm_oblock_t oblock,
159 dm_cblock_t cblock, uint32_t hint, bool hint_valid);
160
161 int (*walk_mappings)(struct dm_cache_policy *p, policy_walk_fn fn,
162 void *context);
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
Joe Thornber532906a2013-11-08 16:36:17 +0000172 /*
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);
Joe Thornberc6b4fcb2013-03-01 22:45:51 +0000179
Joe Thornber532906a2013-11-08 16:36:17 +0000180 /*
Joe Thornber20f68142015-05-15 15:20:09 +0100181 * 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.
Joe Thornber532906a2013-11-08 16:36:17 +0000184 *
185 * Returns:
186 *
187 * 0 and @cblock,@oblock: block to write back provided
188 *
189 * -ENODATA: no dirty blocks available
190 */
Joe Thornber20f68142015-05-15 15:20:09 +0100191 int (*writeback_work)(struct dm_cache_policy *p, dm_oblock_t *oblock, dm_cblock_t *cblock,
192 bool critical_only);
Joe Thornberc6b4fcb2013-03-01 22:45:51 +0000193
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
Joe Thornberfba10102015-05-29 10:20:56 +0100203 * these, the core target sends regular tick() calls to the policy.
Joe Thornberc6b4fcb2013-03-01 22:45:51 +0000204 * The policy should only count an entry as hit once per tick.
205 */
Joe Thornberfba10102015-05-29 10:20:56 +0100206 void (*tick)(struct dm_cache_policy *p, bool can_block);
Joe Thornberc6b4fcb2013-03-01 22:45:51 +0000207
208 /*
209 * Configuration.
210 */
Joe Thornber028ae9f2015-04-22 16:42:35 -0400211 int (*emit_config_values)(struct dm_cache_policy *p, char *result,
212 unsigned maxlen, ssize_t *sz_ptr);
Joe Thornberc6b4fcb2013-03-01 22:45:51 +0000213 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
Mike Snitzer4e7f5062013-03-20 17:21:27 +0000228#define CACHE_POLICY_VERSION_SIZE 3
Joe Thornberc6b4fcb2013-03-01 22:45:51 +0000229
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];
Mike Snitzer4e7f5062013-03-20 17:21:27 +0000239 unsigned version[CACHE_POLICY_VERSION_SIZE];
Joe Thornberc6b4fcb2013-03-01 22:45:51 +0000240
241 /*
Mike Snitzer2e68c4e2014-01-15 21:06:55 -0500242 * 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 /*
Joe Thornberc6b4fcb2013-03-01 22:45:51 +0000248 * 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 */