1 /* SPDX-License-Identifier: GPL-2.0-or-later */
2 /* General filesystem caching backing cache interface
3 *
4 * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 *
7 * NOTE!!! See:
8 *
9 * Documentation/filesystems/caching/backend-api.rst
10 *
11 * for a description of the cache backend interface declared here.
12 */
13
14 #ifndef _LINUX_FSCACHE_CACHE_H
15 #define _LINUX_FSCACHE_CACHE_H
16
17 #include <linux/fscache.h>
18
19 enum fscache_cache_trace;
20 enum fscache_cookie_trace;
21 enum fscache_access_trace;
22
23 enum fscache_cache_state {
24 FSCACHE_CACHE_IS_NOT_PRESENT, /* No cache is present for this name */
25 FSCACHE_CACHE_IS_PREPARING, /* A cache is preparing to come live */
26 FSCACHE_CACHE_IS_ACTIVE, /* Attached cache is active and can be used */
27 FSCACHE_CACHE_GOT_IOERROR, /* Attached cache stopped on I/O error */
28 FSCACHE_CACHE_IS_WITHDRAWN, /* Attached cache is being withdrawn */
29 #define NR__FSCACHE_CACHE_STATE (FSCACHE_CACHE_IS_WITHDRAWN + 1)
30 };
31
32 /*
33 * Cache cookie.
34 */
35 struct fscache_cache {
36 const struct fscache_cache_ops *ops;
37 struct list_head cache_link; /* Link in cache list */
38 void *cache_priv; /* Private cache data (or NULL) */
39 refcount_t ref;
40 atomic_t n_volumes; /* Number of active volumes; */
41 atomic_t n_accesses; /* Number of in-progress accesses on the cache */
42 atomic_t object_count; /* no. of live objects in this cache */
43 unsigned int debug_id;
44 enum fscache_cache_state state;
45 char *name;
46 };
47
48 /*
49 * cache operations
50 */
51 struct fscache_cache_ops {
52 /* name of cache provider */
53 const char *name;
54
55 /* Acquire a volume */
56 void (*acquire_volume)(struct fscache_volume *volume);
57
58 /* Free the cache's data attached to a volume */
59 void (*free_volume)(struct fscache_volume *volume);
60
61 /* Look up a cookie in the cache */
62 bool (*lookup_cookie)(struct fscache_cookie *cookie);
63
64 /* Withdraw an object without any cookie access counts held */
65 void (*withdraw_cookie)(struct fscache_cookie *cookie);
66
67 /* Change the size of a data object */
68 void (*resize_cookie)(struct netfs_cache_resources *cres,
69 loff_t new_size);
70
71 /* Invalidate an object */
72 bool (*invalidate_cookie)(struct fscache_cookie *cookie);
73
74 /* Begin an operation for the netfs lib */
75 bool (*begin_operation)(struct netfs_cache_resources *cres,
76 enum fscache_want_state want_state);
77
78 /* Prepare to write to a live cache object */
79 void (*prepare_to_write)(struct fscache_cookie *cookie);
80 };
81
82 extern struct workqueue_struct *fscache_wq;
83 extern wait_queue_head_t fscache_clearance_waiters;
84
85 /*
86 * out-of-line cache backend functions
87 */
88 extern struct rw_semaphore fscache_addremove_sem;
89 extern struct fscache_cache *fscache_acquire_cache(const char *name);
90 extern void fscache_relinquish_cache(struct fscache_cache *cache);
91 extern int fscache_add_cache(struct fscache_cache *cache,
92 const struct fscache_cache_ops *ops,
93 void *cache_priv);
94 extern void fscache_withdraw_cache(struct fscache_cache *cache);
95 extern void fscache_withdraw_volume(struct fscache_volume *volume);
96 extern void fscache_withdraw_cookie(struct fscache_cookie *cookie);
97
98 extern void fscache_io_error(struct fscache_cache *cache);
99
100 extern void fscache_end_volume_access(struct fscache_volume *volume,
101 struct fscache_cookie *cookie,
102 enum fscache_access_trace why);
103
104 extern struct fscache_cookie *fscache_get_cookie(struct fscache_cookie *cookie,
105 enum fscache_cookie_trace where);
106 extern void fscache_put_cookie(struct fscache_cookie *cookie,
107 enum fscache_cookie_trace where);
108 extern void fscache_end_cookie_access(struct fscache_cookie *cookie,
109 enum fscache_access_trace why);
110 extern void fscache_cookie_lookup_negative(struct fscache_cookie *cookie);
111 extern void fscache_resume_after_invalidation(struct fscache_cookie *cookie);
112 extern void fscache_caching_failed(struct fscache_cookie *cookie);
113 extern bool fscache_wait_for_operation(struct netfs_cache_resources *cred,
114 enum fscache_want_state state);
115
116 /**
117 * fscache_cookie_state - Read the state of a cookie
118 * @cookie: The cookie to query
119 *
120 * Get the state of a cookie, imposing an ordering between the cookie contents
121 * and the state value. Paired with fscache_set_cookie_state().
122 */
123 static inline
fscache_cookie_state(struct fscache_cookie * cookie)124 enum fscache_cookie_state fscache_cookie_state(struct fscache_cookie *cookie)
125 {
126 return smp_load_acquire(&cookie->state);
127 }
128
129 /**
130 * fscache_get_key - Get a pointer to the cookie key
131 * @cookie: The cookie to query
132 *
133 * Return a pointer to the where a cookie's key is stored.
134 */
fscache_get_key(struct fscache_cookie * cookie)135 static inline void *fscache_get_key(struct fscache_cookie *cookie)
136 {
137 if (cookie->key_len <= sizeof(cookie->inline_key))
138 return cookie->inline_key;
139 else
140 return cookie->key;
141 }
142
fscache_cres_cookie(struct netfs_cache_resources * cres)143 static inline struct fscache_cookie *fscache_cres_cookie(struct netfs_cache_resources *cres)
144 {
145 return cres->cache_priv;
146 }
147
148 /**
149 * fscache_count_object - Tell fscache that an object has been added
150 * @cache: The cache to account to
151 *
152 * Tell fscache that an object has been added to the cache. This prevents the
153 * cache from tearing down the cache structure until the object is uncounted.
154 */
fscache_count_object(struct fscache_cache * cache)155 static inline void fscache_count_object(struct fscache_cache *cache)
156 {
157 atomic_inc(&cache->object_count);
158 }
159
160 /**
161 * fscache_uncount_object - Tell fscache that an object has been removed
162 * @cache: The cache to account to
163 *
164 * Tell fscache that an object has been removed from the cache and will no
165 * longer be accessed. After this point, the cache cookie may be destroyed.
166 */
fscache_uncount_object(struct fscache_cache * cache)167 static inline void fscache_uncount_object(struct fscache_cache *cache)
168 {
169 if (atomic_dec_and_test(&cache->object_count))
170 wake_up_all(&fscache_clearance_waiters);
171 }
172
173 /**
174 * fscache_wait_for_objects - Wait for all objects to be withdrawn
175 * @cache: The cache to query
176 *
177 * Wait for all extant objects in a cache to finish being withdrawn
178 * and go away.
179 */
fscache_wait_for_objects(struct fscache_cache * cache)180 static inline void fscache_wait_for_objects(struct fscache_cache *cache)
181 {
182 wait_event(fscache_clearance_waiters,
183 atomic_read(&cache->object_count) == 0);
184 }
185
186 #ifdef CONFIG_FSCACHE_STATS
187 extern atomic_t fscache_n_read;
188 extern atomic_t fscache_n_write;
189 extern atomic_t fscache_n_no_write_space;
190 extern atomic_t fscache_n_no_create_space;
191 extern atomic_t fscache_n_culled;
192 #define fscache_count_read() atomic_inc(&fscache_n_read)
193 #define fscache_count_write() atomic_inc(&fscache_n_write)
194 #define fscache_count_no_write_space() atomic_inc(&fscache_n_no_write_space)
195 #define fscache_count_no_create_space() atomic_inc(&fscache_n_no_create_space)
196 #define fscache_count_culled() atomic_inc(&fscache_n_culled)
197 #else
198 #define fscache_count_read() do {} while(0)
199 #define fscache_count_write() do {} while(0)
200 #define fscache_count_no_write_space() do {} while(0)
201 #define fscache_count_no_create_space() do {} while(0)
202 #define fscache_count_culled() do {} while(0)
203 #endif
204
205 #endif /* _LINUX_FSCACHE_CACHE_H */
206