1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* FS-Cache cache handling
3 *
4 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 */
7
8 #define FSCACHE_DEBUG_LEVEL CACHE
9 #include <linux/module.h>
10 #include <linux/slab.h>
11 #include "internal.h"
12
13 LIST_HEAD(fscache_cache_list);
14 DECLARE_RWSEM(fscache_addremove_sem);
15 DECLARE_WAIT_QUEUE_HEAD(fscache_cache_cleared_wq);
16 EXPORT_SYMBOL(fscache_cache_cleared_wq);
17
18 static LIST_HEAD(fscache_cache_tag_list);
19
20 /*
21 * look up a cache tag
22 */
__fscache_lookup_cache_tag(const char * name)23 struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *name)
24 {
25 struct fscache_cache_tag *tag, *xtag;
26
27 /* firstly check for the existence of the tag under read lock */
28 down_read(&fscache_addremove_sem);
29
30 list_for_each_entry(tag, &fscache_cache_tag_list, link) {
31 if (strcmp(tag->name, name) == 0) {
32 atomic_inc(&tag->usage);
33 up_read(&fscache_addremove_sem);
34 return tag;
35 }
36 }
37
38 up_read(&fscache_addremove_sem);
39
40 /* the tag does not exist - create a candidate */
41 xtag = kzalloc(sizeof(*xtag) + strlen(name) + 1, GFP_KERNEL);
42 if (!xtag)
43 /* return a dummy tag if out of memory */
44 return ERR_PTR(-ENOMEM);
45
46 atomic_set(&xtag->usage, 1);
47 strcpy(xtag->name, name);
48
49 /* write lock, search again and add if still not present */
50 down_write(&fscache_addremove_sem);
51
52 list_for_each_entry(tag, &fscache_cache_tag_list, link) {
53 if (strcmp(tag->name, name) == 0) {
54 atomic_inc(&tag->usage);
55 up_write(&fscache_addremove_sem);
56 kfree(xtag);
57 return tag;
58 }
59 }
60
61 list_add_tail(&xtag->link, &fscache_cache_tag_list);
62 up_write(&fscache_addremove_sem);
63 return xtag;
64 }
65
66 /*
67 * release a reference to a cache tag
68 */
__fscache_release_cache_tag(struct fscache_cache_tag * tag)69 void __fscache_release_cache_tag(struct fscache_cache_tag *tag)
70 {
71 if (tag != ERR_PTR(-ENOMEM)) {
72 down_write(&fscache_addremove_sem);
73
74 if (atomic_dec_and_test(&tag->usage))
75 list_del_init(&tag->link);
76 else
77 tag = NULL;
78
79 up_write(&fscache_addremove_sem);
80
81 kfree(tag);
82 }
83 }
84
85 /*
86 * select a cache in which to store an object
87 * - the cache addremove semaphore must be at least read-locked by the caller
88 * - the object will never be an index
89 */
fscache_select_cache_for_object(struct fscache_cookie * cookie)90 struct fscache_cache *fscache_select_cache_for_object(
91 struct fscache_cookie *cookie)
92 {
93 struct fscache_cache_tag *tag;
94 struct fscache_object *object;
95 struct fscache_cache *cache;
96
97 _enter("");
98
99 if (list_empty(&fscache_cache_list)) {
100 _leave(" = NULL [no cache]");
101 return NULL;
102 }
103
104 /* we check the parent to determine the cache to use */
105 spin_lock(&cookie->lock);
106
107 /* the first in the parent's backing list should be the preferred
108 * cache */
109 if (!hlist_empty(&cookie->backing_objects)) {
110 object = hlist_entry(cookie->backing_objects.first,
111 struct fscache_object, cookie_link);
112
113 cache = object->cache;
114 if (fscache_object_is_dying(object) ||
115 test_bit(FSCACHE_IOERROR, &cache->flags))
116 cache = NULL;
117
118 spin_unlock(&cookie->lock);
119 _leave(" = %s [parent]", cache ? cache->tag->name : "NULL");
120 return cache;
121 }
122
123 /* the parent is unbacked */
124 if (cookie->type != FSCACHE_COOKIE_TYPE_INDEX) {
125 /* cookie not an index and is unbacked */
126 spin_unlock(&cookie->lock);
127 _leave(" = NULL [cookie ub,ni]");
128 return NULL;
129 }
130
131 spin_unlock(&cookie->lock);
132
133 if (!cookie->def->select_cache)
134 goto no_preference;
135
136 /* ask the netfs for its preference */
137 tag = cookie->def->select_cache(cookie->parent->netfs_data,
138 cookie->netfs_data);
139 if (!tag)
140 goto no_preference;
141
142 if (tag == ERR_PTR(-ENOMEM)) {
143 _leave(" = NULL [nomem tag]");
144 return NULL;
145 }
146
147 if (!tag->cache) {
148 _leave(" = NULL [unbacked tag]");
149 return NULL;
150 }
151
152 if (test_bit(FSCACHE_IOERROR, &tag->cache->flags))
153 return NULL;
154
155 _leave(" = %s [specific]", tag->name);
156 return tag->cache;
157
158 no_preference:
159 /* netfs has no preference - just select first cache */
160 cache = list_entry(fscache_cache_list.next,
161 struct fscache_cache, link);
162 _leave(" = %s [first]", cache->tag->name);
163 return cache;
164 }
165
166 /**
167 * fscache_init_cache - Initialise a cache record
168 * @cache: The cache record to be initialised
169 * @ops: The cache operations to be installed in that record
170 * @idfmt: Format string to define identifier
171 * @...: sprintf-style arguments
172 *
173 * Initialise a record of a cache and fill in the name.
174 *
175 * See Documentation/filesystems/caching/backend-api.rst for a complete
176 * description.
177 */
fscache_init_cache(struct fscache_cache * cache,const struct fscache_cache_ops * ops,const char * idfmt,...)178 void fscache_init_cache(struct fscache_cache *cache,
179 const struct fscache_cache_ops *ops,
180 const char *idfmt,
181 ...)
182 {
183 va_list va;
184
185 memset(cache, 0, sizeof(*cache));
186
187 cache->ops = ops;
188
189 va_start(va, idfmt);
190 vsnprintf(cache->identifier, sizeof(cache->identifier), idfmt, va);
191 va_end(va);
192
193 INIT_WORK(&cache->op_gc, fscache_operation_gc);
194 INIT_LIST_HEAD(&cache->link);
195 INIT_LIST_HEAD(&cache->object_list);
196 INIT_LIST_HEAD(&cache->op_gc_list);
197 spin_lock_init(&cache->object_list_lock);
198 spin_lock_init(&cache->op_gc_list_lock);
199 }
200 EXPORT_SYMBOL(fscache_init_cache);
201
202 /**
203 * fscache_add_cache - Declare a cache as being open for business
204 * @cache: The record describing the cache
205 * @ifsdef: The record of the cache object describing the top-level index
206 * @tagname: The tag describing this cache
207 *
208 * Add a cache to the system, making it available for netfs's to use.
209 *
210 * See Documentation/filesystems/caching/backend-api.rst for a complete
211 * description.
212 */
fscache_add_cache(struct fscache_cache * cache,struct fscache_object * ifsdef,const char * tagname)213 int fscache_add_cache(struct fscache_cache *cache,
214 struct fscache_object *ifsdef,
215 const char *tagname)
216 {
217 struct fscache_cache_tag *tag;
218
219 ASSERTCMP(ifsdef->cookie, ==, &fscache_fsdef_index);
220 BUG_ON(!cache->ops);
221 BUG_ON(!ifsdef);
222
223 cache->flags = 0;
224 ifsdef->event_mask =
225 ((1 << NR_FSCACHE_OBJECT_EVENTS) - 1) &
226 ~(1 << FSCACHE_OBJECT_EV_CLEARED);
227 __set_bit(FSCACHE_OBJECT_IS_AVAILABLE, &ifsdef->flags);
228
229 if (!tagname)
230 tagname = cache->identifier;
231
232 BUG_ON(!tagname[0]);
233
234 _enter("{%s.%s},,%s", cache->ops->name, cache->identifier, tagname);
235
236 /* we use the cache tag to uniquely identify caches */
237 tag = __fscache_lookup_cache_tag(tagname);
238 if (IS_ERR(tag))
239 goto nomem;
240
241 if (test_and_set_bit(FSCACHE_TAG_RESERVED, &tag->flags))
242 goto tag_in_use;
243
244 cache->kobj = kobject_create_and_add(tagname, fscache_root);
245 if (!cache->kobj)
246 goto error;
247
248 ifsdef->cache = cache;
249 cache->fsdef = ifsdef;
250
251 down_write(&fscache_addremove_sem);
252
253 tag->cache = cache;
254 cache->tag = tag;
255
256 /* add the cache to the list */
257 list_add(&cache->link, &fscache_cache_list);
258
259 /* add the cache's netfs definition index object to the cache's
260 * list */
261 spin_lock(&cache->object_list_lock);
262 list_add_tail(&ifsdef->cache_link, &cache->object_list);
263 spin_unlock(&cache->object_list_lock);
264
265 /* add the cache's netfs definition index object to the top level index
266 * cookie as a known backing object */
267 spin_lock(&fscache_fsdef_index.lock);
268
269 hlist_add_head(&ifsdef->cookie_link,
270 &fscache_fsdef_index.backing_objects);
271
272 refcount_inc(&fscache_fsdef_index.ref);
273
274 /* done */
275 spin_unlock(&fscache_fsdef_index.lock);
276 up_write(&fscache_addremove_sem);
277
278 pr_notice("Cache \"%s\" added (type %s)\n",
279 cache->tag->name, cache->ops->name);
280 kobject_uevent(cache->kobj, KOBJ_ADD);
281
282 _leave(" = 0 [%s]", cache->identifier);
283 return 0;
284
285 tag_in_use:
286 pr_err("Cache tag '%s' already in use\n", tagname);
287 __fscache_release_cache_tag(tag);
288 _leave(" = -EXIST");
289 return -EEXIST;
290
291 error:
292 __fscache_release_cache_tag(tag);
293 _leave(" = -EINVAL");
294 return -EINVAL;
295
296 nomem:
297 _leave(" = -ENOMEM");
298 return -ENOMEM;
299 }
300 EXPORT_SYMBOL(fscache_add_cache);
301
302 /**
303 * fscache_io_error - Note a cache I/O error
304 * @cache: The record describing the cache
305 *
306 * Note that an I/O error occurred in a cache and that it should no longer be
307 * used for anything. This also reports the error into the kernel log.
308 *
309 * See Documentation/filesystems/caching/backend-api.rst for a complete
310 * description.
311 */
fscache_io_error(struct fscache_cache * cache)312 void fscache_io_error(struct fscache_cache *cache)
313 {
314 if (!test_and_set_bit(FSCACHE_IOERROR, &cache->flags))
315 pr_err("Cache '%s' stopped due to I/O error\n",
316 cache->ops->name);
317 }
318 EXPORT_SYMBOL(fscache_io_error);
319
320 /*
321 * request withdrawal of all the objects in a cache
322 * - all the objects being withdrawn are moved onto the supplied list
323 */
fscache_withdraw_all_objects(struct fscache_cache * cache,struct list_head * dying_objects)324 static void fscache_withdraw_all_objects(struct fscache_cache *cache,
325 struct list_head *dying_objects)
326 {
327 struct fscache_object *object;
328
329 while (!list_empty(&cache->object_list)) {
330 spin_lock(&cache->object_list_lock);
331
332 if (!list_empty(&cache->object_list)) {
333 object = list_entry(cache->object_list.next,
334 struct fscache_object, cache_link);
335 list_move_tail(&object->cache_link, dying_objects);
336
337 _debug("withdraw %x", object->cookie->debug_id);
338
339 /* This must be done under object_list_lock to prevent
340 * a race with fscache_drop_object().
341 */
342 fscache_raise_event(object, FSCACHE_OBJECT_EV_KILL);
343 }
344
345 spin_unlock(&cache->object_list_lock);
346 cond_resched();
347 }
348 }
349
350 /**
351 * fscache_withdraw_cache - Withdraw a cache from the active service
352 * @cache: The record describing the cache
353 *
354 * Withdraw a cache from service, unbinding all its cache objects from the
355 * netfs cookies they're currently representing.
356 *
357 * See Documentation/filesystems/caching/backend-api.rst for a complete
358 * description.
359 */
fscache_withdraw_cache(struct fscache_cache * cache)360 void fscache_withdraw_cache(struct fscache_cache *cache)
361 {
362 LIST_HEAD(dying_objects);
363
364 _enter("");
365
366 pr_notice("Withdrawing cache \"%s\"\n",
367 cache->tag->name);
368
369 /* make the cache unavailable for cookie acquisition */
370 if (test_and_set_bit(FSCACHE_CACHE_WITHDRAWN, &cache->flags))
371 BUG();
372
373 down_write(&fscache_addremove_sem);
374 list_del_init(&cache->link);
375 cache->tag->cache = NULL;
376 up_write(&fscache_addremove_sem);
377
378 /* make sure all pages pinned by operations on behalf of the netfs are
379 * written to disk */
380 fscache_stat(&fscache_n_cop_sync_cache);
381 cache->ops->sync_cache(cache);
382 fscache_stat_d(&fscache_n_cop_sync_cache);
383
384 /* dissociate all the netfs pages backed by this cache from the block
385 * mappings in the cache */
386 fscache_stat(&fscache_n_cop_dissociate_pages);
387 cache->ops->dissociate_pages(cache);
388 fscache_stat_d(&fscache_n_cop_dissociate_pages);
389
390 /* we now have to destroy all the active objects pertaining to this
391 * cache - which we do by passing them off to thread pool to be
392 * disposed of */
393 _debug("destroy");
394
395 fscache_withdraw_all_objects(cache, &dying_objects);
396
397 /* wait for all extant objects to finish their outstanding operations
398 * and go away */
399 _debug("wait for finish");
400 wait_event(fscache_cache_cleared_wq,
401 atomic_read(&cache->object_count) == 0);
402 _debug("wait for clearance");
403 wait_event(fscache_cache_cleared_wq,
404 list_empty(&cache->object_list));
405 _debug("cleared");
406 ASSERT(list_empty(&dying_objects));
407
408 kobject_put(cache->kobj);
409
410 clear_bit(FSCACHE_TAG_RESERVED, &cache->tag->flags);
411 fscache_release_cache_tag(cache->tag);
412 cache->tag = NULL;
413
414 _leave("");
415 }
416 EXPORT_SYMBOL(fscache_withdraw_cache);
417
