1 /* FS-Cache cache handling
2  *
3  * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
4  * Written by David Howells (dhowells@redhat.com)
5  *
6  * This program is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU General Public License
8  * as published by the Free Software Foundation; either version
9  * 2 of the License, or (at your option) any later version.
10  */
11 
12 #define FSCACHE_DEBUG_LEVEL CACHE
13 #include <linux/module.h>
14 #include <linux/slab.h>
15 #include "internal.h"
16 
17 LIST_HEAD(fscache_cache_list);
18 DECLARE_RWSEM(fscache_addremove_sem);
19 DECLARE_WAIT_QUEUE_HEAD(fscache_cache_cleared_wq);
20 EXPORT_SYMBOL(fscache_cache_cleared_wq);
21 
22 static LIST_HEAD(fscache_cache_tag_list);
23 
24 /*
25  * look up a cache tag
26  */
__fscache_lookup_cache_tag(const char * name)27 struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *name)
28 {
29 	struct fscache_cache_tag *tag, *xtag;
30 
31 	/* firstly check for the existence of the tag under read lock */
32 	down_read(&fscache_addremove_sem);
33 
34 	list_for_each_entry(tag, &fscache_cache_tag_list, link) {
35 		if (strcmp(tag->name, name) == 0) {
36 			atomic_inc(&tag->usage);
37 			up_read(&fscache_addremove_sem);
38 			return tag;
39 		}
40 	}
41 
42 	up_read(&fscache_addremove_sem);
43 
44 	/* the tag does not exist - create a candidate */
45 	xtag = kzalloc(sizeof(*xtag) + strlen(name) + 1, GFP_KERNEL);
46 	if (!xtag)
47 		/* return a dummy tag if out of memory */
48 		return ERR_PTR(-ENOMEM);
49 
50 	atomic_set(&xtag->usage, 1);
51 	strcpy(xtag->name, name);
52 
53 	/* write lock, search again and add if still not present */
54 	down_write(&fscache_addremove_sem);
55 
56 	list_for_each_entry(tag, &fscache_cache_tag_list, link) {
57 		if (strcmp(tag->name, name) == 0) {
58 			atomic_inc(&tag->usage);
59 			up_write(&fscache_addremove_sem);
60 			kfree(xtag);
61 			return tag;
62 		}
63 	}
64 
65 	list_add_tail(&xtag->link, &fscache_cache_tag_list);
66 	up_write(&fscache_addremove_sem);
67 	return xtag;
68 }
69 
70 /*
71  * release a reference to a cache tag
72  */
__fscache_release_cache_tag(struct fscache_cache_tag * tag)73 void __fscache_release_cache_tag(struct fscache_cache_tag *tag)
74 {
75 	if (tag != ERR_PTR(-ENOMEM)) {
76 		down_write(&fscache_addremove_sem);
77 
78 		if (atomic_dec_and_test(&tag->usage))
79 			list_del_init(&tag->link);
80 		else
81 			tag = NULL;
82 
83 		up_write(&fscache_addremove_sem);
84 
85 		kfree(tag);
86 	}
87 }
88 
89 /*
90  * select a cache in which to store an object
91  * - the cache addremove semaphore must be at least read-locked by the caller
92  * - the object will never be an index
93  */
fscache_select_cache_for_object(struct fscache_cookie * cookie)94 struct fscache_cache *fscache_select_cache_for_object(
95 	struct fscache_cookie *cookie)
96 {
97 	struct fscache_cache_tag *tag;
98 	struct fscache_object *object;
99 	struct fscache_cache *cache;
100 
101 	_enter("");
102 
103 	if (list_empty(&fscache_cache_list)) {
104 		_leave(" = NULL [no cache]");
105 		return NULL;
106 	}
107 
108 	/* we check the parent to determine the cache to use */
109 	spin_lock(&cookie->lock);
110 
111 	/* the first in the parent's backing list should be the preferred
112 	 * cache */
113 	if (!hlist_empty(&cookie->backing_objects)) {
114 		object = hlist_entry(cookie->backing_objects.first,
115 				     struct fscache_object, cookie_link);
116 
117 		cache = object->cache;
118 		if (fscache_object_is_dying(object) ||
119 		    test_bit(FSCACHE_IOERROR, &cache->flags))
120 			cache = NULL;
121 
122 		spin_unlock(&cookie->lock);
123 		_leave(" = %p [parent]", cache);
124 		return cache;
125 	}
126 
127 	/* the parent is unbacked */
128 	if (cookie->type != FSCACHE_COOKIE_TYPE_INDEX) {
129 		/* cookie not an index and is unbacked */
130 		spin_unlock(&cookie->lock);
131 		_leave(" = NULL [cookie ub,ni]");
132 		return NULL;
133 	}
134 
135 	spin_unlock(&cookie->lock);
136 
137 	if (!cookie->def->select_cache)
138 		goto no_preference;
139 
140 	/* ask the netfs for its preference */
141 	tag = cookie->def->select_cache(cookie->parent->netfs_data,
142 					cookie->netfs_data);
143 	if (!tag)
144 		goto no_preference;
145 
146 	if (tag == ERR_PTR(-ENOMEM)) {
147 		_leave(" = NULL [nomem tag]");
148 		return NULL;
149 	}
150 
151 	if (!tag->cache) {
152 		_leave(" = NULL [unbacked tag]");
153 		return NULL;
154 	}
155 
156 	if (test_bit(FSCACHE_IOERROR, &tag->cache->flags))
157 		return NULL;
158 
159 	_leave(" = %p [specific]", tag->cache);
160 	return tag->cache;
161 
162 no_preference:
163 	/* netfs has no preference - just select first cache */
164 	cache = list_entry(fscache_cache_list.next,
165 			   struct fscache_cache, link);
166 	_leave(" = %p [first]", cache);
167 	return cache;
168 }
169 
170 /**
171  * fscache_init_cache - Initialise a cache record
172  * @cache: The cache record to be initialised
173  * @ops: The cache operations to be installed in that record
174  * @idfmt: Format string to define identifier
175  * @...: sprintf-style arguments
176  *
177  * Initialise a record of a cache and fill in the name.
178  *
179  * See Documentation/filesystems/caching/backend-api.txt for a complete
180  * description.
181  */
fscache_init_cache(struct fscache_cache * cache,const struct fscache_cache_ops * ops,const char * idfmt,...)182 void fscache_init_cache(struct fscache_cache *cache,
183 			const struct fscache_cache_ops *ops,
184 			const char *idfmt,
185 			...)
186 {
187 	va_list va;
188 
189 	memset(cache, 0, sizeof(*cache));
190 
191 	cache->ops = ops;
192 
193 	va_start(va, idfmt);
194 	vsnprintf(cache->identifier, sizeof(cache->identifier), idfmt, va);
195 	va_end(va);
196 
197 	INIT_WORK(&cache->op_gc, fscache_operation_gc);
198 	INIT_LIST_HEAD(&cache->link);
199 	INIT_LIST_HEAD(&cache->object_list);
200 	INIT_LIST_HEAD(&cache->op_gc_list);
201 	spin_lock_init(&cache->object_list_lock);
202 	spin_lock_init(&cache->op_gc_list_lock);
203 }
204 EXPORT_SYMBOL(fscache_init_cache);
205 
206 /**
207  * fscache_add_cache - Declare a cache as being open for business
208  * @cache: The record describing the cache
209  * @ifsdef: The record of the cache object describing the top-level index
210  * @tagname: The tag describing this cache
211  *
212  * Add a cache to the system, making it available for netfs's to use.
213  *
214  * See Documentation/filesystems/caching/backend-api.txt for a complete
215  * description.
216  */
fscache_add_cache(struct fscache_cache * cache,struct fscache_object * ifsdef,const char * tagname)217 int fscache_add_cache(struct fscache_cache *cache,
218 		      struct fscache_object *ifsdef,
219 		      const char *tagname)
220 {
221 	struct fscache_cache_tag *tag;
222 
223 	ASSERTCMP(ifsdef->cookie, ==, &fscache_fsdef_index);
224 	BUG_ON(!cache->ops);
225 	BUG_ON(!ifsdef);
226 
227 	cache->flags = 0;
228 	ifsdef->event_mask =
229 		((1 << NR_FSCACHE_OBJECT_EVENTS) - 1) &
230 		~(1 << FSCACHE_OBJECT_EV_CLEARED);
231 	__set_bit(FSCACHE_OBJECT_IS_AVAILABLE, &ifsdef->flags);
232 
233 	if (!tagname)
234 		tagname = cache->identifier;
235 
236 	BUG_ON(!tagname[0]);
237 
238 	_enter("{%s.%s},,%s", cache->ops->name, cache->identifier, tagname);
239 
240 	/* we use the cache tag to uniquely identify caches */
241 	tag = __fscache_lookup_cache_tag(tagname);
242 	if (IS_ERR(tag))
243 		goto nomem;
244 
245 	if (test_and_set_bit(FSCACHE_TAG_RESERVED, &tag->flags))
246 		goto tag_in_use;
247 
248 	cache->kobj = kobject_create_and_add(tagname, fscache_root);
249 	if (!cache->kobj)
250 		goto error;
251 
252 	ifsdef->cache = cache;
253 	cache->fsdef = ifsdef;
254 
255 	down_write(&fscache_addremove_sem);
256 
257 	tag->cache = cache;
258 	cache->tag = tag;
259 
260 	/* add the cache to the list */
261 	list_add(&cache->link, &fscache_cache_list);
262 
263 	/* add the cache's netfs definition index object to the cache's
264 	 * list */
265 	spin_lock(&cache->object_list_lock);
266 	list_add_tail(&ifsdef->cache_link, &cache->object_list);
267 	spin_unlock(&cache->object_list_lock);
268 	fscache_objlist_add(ifsdef);
269 
270 	/* add the cache's netfs definition index object to the top level index
271 	 * cookie as a known backing object */
272 	spin_lock(&fscache_fsdef_index.lock);
273 
274 	hlist_add_head(&ifsdef->cookie_link,
275 		       &fscache_fsdef_index.backing_objects);
276 
277 	atomic_inc(&fscache_fsdef_index.usage);
278 
279 	/* done */
280 	spin_unlock(&fscache_fsdef_index.lock);
281 	up_write(&fscache_addremove_sem);
282 
283 	pr_notice("Cache \"%s\" added (type %s)\n",
284 		  cache->tag->name, cache->ops->name);
285 	kobject_uevent(cache->kobj, KOBJ_ADD);
286 
287 	_leave(" = 0 [%s]", cache->identifier);
288 	return 0;
289 
290 tag_in_use:
291 	pr_err("Cache tag '%s' already in use\n", tagname);
292 	__fscache_release_cache_tag(tag);
293 	_leave(" = -EXIST");
294 	return -EEXIST;
295 
296 error:
297 	__fscache_release_cache_tag(tag);
298 	_leave(" = -EINVAL");
299 	return -EINVAL;
300 
301 nomem:
302 	_leave(" = -ENOMEM");
303 	return -ENOMEM;
304 }
305 EXPORT_SYMBOL(fscache_add_cache);
306 
307 /**
308  * fscache_io_error - Note a cache I/O error
309  * @cache: The record describing the cache
310  *
311  * Note that an I/O error occurred in a cache and that it should no longer be
312  * used for anything.  This also reports the error into the kernel log.
313  *
314  * See Documentation/filesystems/caching/backend-api.txt for a complete
315  * description.
316  */
fscache_io_error(struct fscache_cache * cache)317 void fscache_io_error(struct fscache_cache *cache)
318 {
319 	if (!test_and_set_bit(FSCACHE_IOERROR, &cache->flags))
320 		pr_err("Cache '%s' stopped due to I/O error\n",
321 		       cache->ops->name);
322 }
323 EXPORT_SYMBOL(fscache_io_error);
324 
325 /*
326  * request withdrawal of all the objects in a cache
327  * - all the objects being withdrawn are moved onto the supplied list
328  */
fscache_withdraw_all_objects(struct fscache_cache * cache,struct list_head * dying_objects)329 static void fscache_withdraw_all_objects(struct fscache_cache *cache,
330 					 struct list_head *dying_objects)
331 {
332 	struct fscache_object *object;
333 
334 	while (!list_empty(&cache->object_list)) {
335 		spin_lock(&cache->object_list_lock);
336 
337 		if (!list_empty(&cache->object_list)) {
338 			object = list_entry(cache->object_list.next,
339 					    struct fscache_object, cache_link);
340 			list_move_tail(&object->cache_link, dying_objects);
341 
342 			_debug("withdraw %p", object->cookie);
343 
344 			/* This must be done under object_list_lock to prevent
345 			 * a race with fscache_drop_object().
346 			 */
347 			fscache_raise_event(object, FSCACHE_OBJECT_EV_KILL);
348 		}
349 
350 		spin_unlock(&cache->object_list_lock);
351 		cond_resched();
352 	}
353 }
354 
355 /**
356  * fscache_withdraw_cache - Withdraw a cache from the active service
357  * @cache: The record describing the cache
358  *
359  * Withdraw a cache from service, unbinding all its cache objects from the
360  * netfs cookies they're currently representing.
361  *
362  * See Documentation/filesystems/caching/backend-api.txt for a complete
363  * description.
364  */
fscache_withdraw_cache(struct fscache_cache * cache)365 void fscache_withdraw_cache(struct fscache_cache *cache)
366 {
367 	LIST_HEAD(dying_objects);
368 
369 	_enter("");
370 
371 	pr_notice("Withdrawing cache \"%s\"\n",
372 		  cache->tag->name);
373 
374 	/* make the cache unavailable for cookie acquisition */
375 	if (test_and_set_bit(FSCACHE_CACHE_WITHDRAWN, &cache->flags))
376 		BUG();
377 
378 	down_write(&fscache_addremove_sem);
379 	list_del_init(&cache->link);
380 	cache->tag->cache = NULL;
381 	up_write(&fscache_addremove_sem);
382 
383 	/* make sure all pages pinned by operations on behalf of the netfs are
384 	 * written to disk */
385 	fscache_stat(&fscache_n_cop_sync_cache);
386 	cache->ops->sync_cache(cache);
387 	fscache_stat_d(&fscache_n_cop_sync_cache);
388 
389 	/* dissociate all the netfs pages backed by this cache from the block
390 	 * mappings in the cache */
391 	fscache_stat(&fscache_n_cop_dissociate_pages);
392 	cache->ops->dissociate_pages(cache);
393 	fscache_stat_d(&fscache_n_cop_dissociate_pages);
394 
395 	/* we now have to destroy all the active objects pertaining to this
396 	 * cache - which we do by passing them off to thread pool to be
397 	 * disposed of */
398 	_debug("destroy");
399 
400 	fscache_withdraw_all_objects(cache, &dying_objects);
401 
402 	/* wait for all extant objects to finish their outstanding operations
403 	 * and go away */
404 	_debug("wait for finish");
405 	wait_event(fscache_cache_cleared_wq,
406 		   atomic_read(&cache->object_count) == 0);
407 	_debug("wait for clearance");
408 	wait_event(fscache_cache_cleared_wq,
409 		   list_empty(&cache->object_list));
410 	_debug("cleared");
411 	ASSERT(list_empty(&dying_objects));
412 
413 	kobject_put(cache->kobj);
414 
415 	clear_bit(FSCACHE_TAG_RESERVED, &cache->tag->flags);
416 	fscache_release_cache_tag(cache->tag);
417 	cache->tag = NULL;
418 
419 	_leave("");
420 }
421 EXPORT_SYMBOL(fscache_withdraw_cache);
422