fscache-cache.h

  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 29	FSCACHE_CACHE_IS_WITHDRAWN,	/* Attached cache is being withdrawn */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(&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(&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 */