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
19enum fscache_cache_trace;
20enum fscache_cookie_trace;
21enum fscache_access_trace;
22enum fscache_volume_trace;
23
24enum fscache_cache_state {
25 FSCACHE_CACHE_IS_NOT_PRESENT, /* No cache is present for this name */
26 FSCACHE_CACHE_IS_PREPARING, /* A cache is preparing to come live */
27 FSCACHE_CACHE_IS_ACTIVE, /* Attached cache is active and can be used */
28 FSCACHE_CACHE_GOT_IOERROR, /* Attached cache stopped on I/O error */
29 FSCACHE_CACHE_IS_WITHDRAWN, /* Attached cache is being withdrawn */
30#define NR__FSCACHE_CACHE_STATE (FSCACHE_CACHE_IS_WITHDRAWN + 1)
31};
32
33/*
34 * Cache cookie.
35 */
36struct fscache_cache {
37 const struct fscache_cache_ops *ops;
38 struct list_head cache_link; /* Link in cache list */
39 void *cache_priv; /* Private cache data (or NULL) */
40 refcount_t ref;
41 atomic_t n_volumes; /* Number of active volumes; */
42 atomic_t n_accesses; /* Number of in-progress accesses on the cache */
43 atomic_t object_count; /* no. of live objects in this cache */
44 unsigned int debug_id;
45 enum fscache_cache_state state;
46 char *name;
47};
48
49/*
50 * cache operations
51 */
52struct fscache_cache_ops {
53 /* name of cache provider */
54 const char *name;
55
56 /* Acquire a volume */
57 void (*acquire_volume)(struct fscache_volume *volume);
58
59 /* Free the cache's data attached to a volume */
60 void (*free_volume)(struct fscache_volume *volume);
61
62 /* Look up a cookie in the cache */
63 bool (*lookup_cookie)(struct fscache_cookie *cookie);
64
65 /* Withdraw an object without any cookie access counts held */
66 void (*withdraw_cookie)(struct fscache_cookie *cookie);
67
68 /* Change the size of a data object */
69 void (*resize_cookie)(struct netfs_cache_resources *cres,
70 loff_t new_size);
71
72 /* Invalidate an object */
73 bool (*invalidate_cookie)(struct fscache_cookie *cookie);
74
75 /* Begin an operation for the netfs lib */
76 bool (*begin_operation)(struct netfs_cache_resources *cres,
77 enum fscache_want_state want_state);
78
79 /* Prepare to write to a live cache object */
80 void (*prepare_to_write)(struct fscache_cookie *cookie);
81};
82
83extern struct workqueue_struct *fscache_wq;
84extern wait_queue_head_t fscache_clearance_waiters;
85
86/*
87 * out-of-line cache backend functions
88 */
89extern struct rw_semaphore fscache_addremove_sem;
90extern struct fscache_cache *fscache_acquire_cache(const char *name);
91extern void fscache_relinquish_cache(struct fscache_cache *cache);
92extern int fscache_add_cache(struct fscache_cache *cache,
93 const struct fscache_cache_ops *ops,
94 void *cache_priv);
95extern void fscache_withdraw_cache(struct fscache_cache *cache);
96extern void fscache_withdraw_volume(struct fscache_volume *volume);
97extern void fscache_withdraw_cookie(struct fscache_cookie *cookie);
98
99extern void fscache_io_error(struct fscache_cache *cache);
100
101extern struct fscache_volume *
102fscache_try_get_volume(struct fscache_volume *volume,
103 enum fscache_volume_trace where);
104extern void fscache_put_volume(struct fscache_volume *volume,
105 enum fscache_volume_trace where);
106extern void fscache_end_volume_access(struct fscache_volume *volume,
107 struct fscache_cookie *cookie,
108 enum fscache_access_trace why);
109
110extern struct fscache_cookie *fscache_get_cookie(struct fscache_cookie *cookie,
111 enum fscache_cookie_trace where);
112extern void fscache_put_cookie(struct fscache_cookie *cookie,
113 enum fscache_cookie_trace where);
114extern void fscache_end_cookie_access(struct fscache_cookie *cookie,
115 enum fscache_access_trace why);
116extern void fscache_cookie_lookup_negative(struct fscache_cookie *cookie);
117extern void fscache_resume_after_invalidation(struct fscache_cookie *cookie);
118extern void fscache_caching_failed(struct fscache_cookie *cookie);
119extern bool fscache_wait_for_operation(struct netfs_cache_resources *cred,
120 enum fscache_want_state state);
121
122/**
123 * fscache_cookie_state - Read the state of a cookie
124 * @cookie: The cookie to query
125 *
126 * Get the state of a cookie, imposing an ordering between the cookie contents
127 * and the state value. Paired with fscache_set_cookie_state().
128 */
129static inline
130enum fscache_cookie_state fscache_cookie_state(struct fscache_cookie *cookie)
131{
132 return smp_load_acquire(&cookie->state);
133}
134
135/**
136 * fscache_get_key - Get a pointer to the cookie key
137 * @cookie: The cookie to query
138 *
139 * Return a pointer to the where a cookie's key is stored.
140 */
141static inline void *fscache_get_key(struct fscache_cookie *cookie)
142{
143 if (cookie->key_len <= sizeof(cookie->inline_key))
144 return cookie->inline_key;
145 else
146 return cookie->key;
147}
148
149static inline struct fscache_cookie *fscache_cres_cookie(struct netfs_cache_resources *cres)
150{
151 return cres->cache_priv;
152}
153
154/**
155 * fscache_count_object - Tell fscache that an object has been added
156 * @cache: The cache to account to
157 *
158 * Tell fscache that an object has been added to the cache. This prevents the
159 * cache from tearing down the cache structure until the object is uncounted.
160 */
161static inline void fscache_count_object(struct fscache_cache *cache)
162{
163 atomic_inc(v: &cache->object_count);
164}
165
166/**
167 * fscache_uncount_object - Tell fscache that an object has been removed
168 * @cache: The cache to account to
169 *
170 * Tell fscache that an object has been removed from the cache and will no
171 * longer be accessed. After this point, the cache cookie may be destroyed.
172 */
173static inline void fscache_uncount_object(struct fscache_cache *cache)
174{
175 if (atomic_dec_and_test(v: &cache->object_count))
176 wake_up_all(&fscache_clearance_waiters);
177}
178
179/**
180 * fscache_wait_for_objects - Wait for all objects to be withdrawn
181 * @cache: The cache to query
182 *
183 * Wait for all extant objects in a cache to finish being withdrawn
184 * and go away.
185 */
186static inline void fscache_wait_for_objects(struct fscache_cache *cache)
187{
188 wait_event(fscache_clearance_waiters,
189 atomic_read(&cache->object_count) == 0);
190}
191
192#ifdef CONFIG_FSCACHE_STATS
193extern atomic_t fscache_n_read;
194extern atomic_t fscache_n_write;
195extern atomic_t fscache_n_no_write_space;
196extern atomic_t fscache_n_no_create_space;
197extern atomic_t fscache_n_culled;
198extern atomic_t fscache_n_dio_misfit;
199#define fscache_count_read() atomic_inc(&fscache_n_read)
200#define fscache_count_write() atomic_inc(&fscache_n_write)
201#define fscache_count_no_write_space() atomic_inc(&fscache_n_no_write_space)
202#define fscache_count_no_create_space() atomic_inc(&fscache_n_no_create_space)
203#define fscache_count_culled() atomic_inc(&fscache_n_culled)
204#define fscache_count_dio_misfit() atomic_inc(&fscache_n_dio_misfit)
205#else
206#define fscache_count_read() do {} while(0)
207#define fscache_count_write() do {} while(0)
208#define fscache_count_no_write_space() do {} while(0)
209#define fscache_count_no_create_space() do {} while(0)
210#define fscache_count_culled() do {} while(0)
211#define fscache_count_dio_misfit() do {} while(0)
212#endif
213
214#endif /* _LINUX_FSCACHE_CACHE_H */
215

source code of linux/include/linux/fscache-cache.h

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