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28 	FSCACHE_CACHE_IS_WITHDRAWN,	/* Attached cache is being withdrawn */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