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 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 */
187