1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3    lru_cache.c
4 
5    This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
6 
7    Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
8    Copyright (C) 2003-2008, Philipp Reisner <philipp.reisner@linbit.com>.
9    Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
10 
11 
12  */
13 
14 #include <linux/module.h>
15 #include <linux/bitops.h>
16 #include <linux/slab.h>
17 #include <linux/string.h> /* for memset */
18 #include <linux/seq_file.h> /* for seq_printf */
19 #include <linux/lru_cache.h>
20 
21 MODULE_AUTHOR("Philipp Reisner <phil@linbit.com>, "
22 	      "Lars Ellenberg <lars@linbit.com>");
23 MODULE_DESCRIPTION("lru_cache - Track sets of hot objects");
24 MODULE_LICENSE("GPL");
25 
26 /* this is developers aid only.
27  * it catches concurrent access (lack of locking on the users part) */
28 #define PARANOIA_ENTRY() do {		\
29 	BUG_ON(!lc);			\
30 	BUG_ON(!lc->nr_elements);	\
31 	BUG_ON(test_and_set_bit(__LC_PARANOIA, &lc->flags)); \
32 } while (0)
33 
34 #define RETURN(x...)     do { \
35 	clear_bit_unlock(__LC_PARANOIA, &lc->flags); \
36 	return x ; } while (0)
37 
38 /* BUG() if e is not one of the elements tracked by lc */
39 #define PARANOIA_LC_ELEMENT(lc, e) do {	\
40 	struct lru_cache *lc_ = (lc);	\
41 	struct lc_element *e_ = (e);	\
42 	unsigned i = e_->lc_index;	\
43 	BUG_ON(i >= lc_->nr_elements);	\
44 	BUG_ON(lc_->lc_element[i] != e_); } while (0)
45 
46 
47 /* We need to atomically
48  *  - try to grab the lock (set LC_LOCKED)
49  *  - only if there is no pending transaction
50  *    (neither LC_DIRTY nor LC_STARVING is set)
51  * Because of PARANOIA_ENTRY() above abusing lc->flags as well,
52  * it is not sufficient to just say
53  *	return 0 == cmpxchg(&lc->flags, 0, LC_LOCKED);
54  */
lc_try_lock(struct lru_cache * lc)55 int lc_try_lock(struct lru_cache *lc)
56 {
57 	unsigned long val;
58 	do {
59 		val = cmpxchg(&lc->flags, 0, LC_LOCKED);
60 	} while (unlikely (val == LC_PARANOIA));
61 	/* Spin until no-one is inside a PARANOIA_ENTRY()/RETURN() section. */
62 	return 0 == val;
63 #if 0
64 	/* Alternative approach, spin in case someone enters or leaves a
65 	 * PARANOIA_ENTRY()/RETURN() section. */
66 	unsigned long old, new, val;
67 	do {
68 		old = lc->flags & LC_PARANOIA;
69 		new = old | LC_LOCKED;
70 		val = cmpxchg(&lc->flags, old, new);
71 	} while (unlikely (val == (old ^ LC_PARANOIA)));
72 	return old == val;
73 #endif
74 }
75 
76 /**
77  * lc_create - prepares to track objects in an active set
78  * @name: descriptive name only used in lc_seq_printf_stats and lc_seq_dump_details
79  * @cache: cache root pointer
80  * @max_pending_changes: maximum changes to accumulate until a transaction is required
81  * @e_count: number of elements allowed to be active simultaneously
82  * @e_size: size of the tracked objects
83  * @e_off: offset to the &struct lc_element member in a tracked object
84  *
85  * Returns a pointer to a newly initialized struct lru_cache on success,
86  * or NULL on (allocation) failure.
87  */
lc_create(const char * name,struct kmem_cache * cache,unsigned max_pending_changes,unsigned e_count,size_t e_size,size_t e_off)88 struct lru_cache *lc_create(const char *name, struct kmem_cache *cache,
89 		unsigned max_pending_changes,
90 		unsigned e_count, size_t e_size, size_t e_off)
91 {
92 	struct hlist_head *slot = NULL;
93 	struct lc_element **element = NULL;
94 	struct lru_cache *lc;
95 	struct lc_element *e;
96 	unsigned cache_obj_size = kmem_cache_size(cache);
97 	unsigned i;
98 
99 	WARN_ON(cache_obj_size < e_size);
100 	if (cache_obj_size < e_size)
101 		return NULL;
102 
103 	/* e_count too big; would probably fail the allocation below anyways.
104 	 * for typical use cases, e_count should be few thousand at most. */
105 	if (e_count > LC_MAX_ACTIVE)
106 		return NULL;
107 
108 	slot = kcalloc(e_count, sizeof(struct hlist_head), GFP_KERNEL);
109 	if (!slot)
110 		goto out_fail;
111 	element = kcalloc(e_count, sizeof(struct lc_element *), GFP_KERNEL);
112 	if (!element)
113 		goto out_fail;
114 
115 	lc = kzalloc(sizeof(*lc), GFP_KERNEL);
116 	if (!lc)
117 		goto out_fail;
118 
119 	INIT_LIST_HEAD(&lc->in_use);
120 	INIT_LIST_HEAD(&lc->lru);
121 	INIT_LIST_HEAD(&lc->free);
122 	INIT_LIST_HEAD(&lc->to_be_changed);
123 
124 	lc->name = name;
125 	lc->element_size = e_size;
126 	lc->element_off = e_off;
127 	lc->nr_elements = e_count;
128 	lc->max_pending_changes = max_pending_changes;
129 	lc->lc_cache = cache;
130 	lc->lc_element = element;
131 	lc->lc_slot = slot;
132 
133 	/* preallocate all objects */
134 	for (i = 0; i < e_count; i++) {
135 		void *p = kmem_cache_alloc(cache, GFP_KERNEL);
136 		if (!p)
137 			break;
138 		memset(p, 0, lc->element_size);
139 		e = p + e_off;
140 		e->lc_index = i;
141 		e->lc_number = LC_FREE;
142 		e->lc_new_number = LC_FREE;
143 		list_add(&e->list, &lc->free);
144 		element[i] = e;
145 	}
146 	if (i == e_count)
147 		return lc;
148 
149 	/* else: could not allocate all elements, give up */
150 	for (i--; i; i--) {
151 		void *p = element[i];
152 		kmem_cache_free(cache, p - e_off);
153 	}
154 	kfree(lc);
155 out_fail:
156 	kfree(element);
157 	kfree(slot);
158 	return NULL;
159 }
160 
lc_free_by_index(struct lru_cache * lc,unsigned i)161 static void lc_free_by_index(struct lru_cache *lc, unsigned i)
162 {
163 	void *p = lc->lc_element[i];
164 	WARN_ON(!p);
165 	if (p) {
166 		p -= lc->element_off;
167 		kmem_cache_free(lc->lc_cache, p);
168 	}
169 }
170 
171 /**
172  * lc_destroy - frees memory allocated by lc_create()
173  * @lc: the lru cache to destroy
174  */
lc_destroy(struct lru_cache * lc)175 void lc_destroy(struct lru_cache *lc)
176 {
177 	unsigned i;
178 	if (!lc)
179 		return;
180 	for (i = 0; i < lc->nr_elements; i++)
181 		lc_free_by_index(lc, i);
182 	kfree(lc->lc_element);
183 	kfree(lc->lc_slot);
184 	kfree(lc);
185 }
186 
187 /**
188  * lc_reset - does a full reset for @lc and the hash table slots.
189  * @lc: the lru cache to operate on
190  *
191  * It is roughly the equivalent of re-allocating a fresh lru_cache object,
192  * basically a short cut to lc_destroy(lc); lc = lc_create(...);
193  */
lc_reset(struct lru_cache * lc)194 void lc_reset(struct lru_cache *lc)
195 {
196 	unsigned i;
197 
198 	INIT_LIST_HEAD(&lc->in_use);
199 	INIT_LIST_HEAD(&lc->lru);
200 	INIT_LIST_HEAD(&lc->free);
201 	INIT_LIST_HEAD(&lc->to_be_changed);
202 	lc->used = 0;
203 	lc->hits = 0;
204 	lc->misses = 0;
205 	lc->starving = 0;
206 	lc->locked = 0;
207 	lc->changed = 0;
208 	lc->pending_changes = 0;
209 	lc->flags = 0;
210 	memset(lc->lc_slot, 0, sizeof(struct hlist_head) * lc->nr_elements);
211 
212 	for (i = 0; i < lc->nr_elements; i++) {
213 		struct lc_element *e = lc->lc_element[i];
214 		void *p = e;
215 		p -= lc->element_off;
216 		memset(p, 0, lc->element_size);
217 		/* re-init it */
218 		e->lc_index = i;
219 		e->lc_number = LC_FREE;
220 		e->lc_new_number = LC_FREE;
221 		list_add(&e->list, &lc->free);
222 	}
223 }
224 
225 /**
226  * lc_seq_printf_stats - print stats about @lc into @seq
227  * @seq: the seq_file to print into
228  * @lc: the lru cache to print statistics of
229  */
lc_seq_printf_stats(struct seq_file * seq,struct lru_cache * lc)230 void lc_seq_printf_stats(struct seq_file *seq, struct lru_cache *lc)
231 {
232 	/* NOTE:
233 	 * total calls to lc_get are
234 	 * (starving + hits + misses)
235 	 * misses include "locked" count (update from an other thread in
236 	 * progress) and "changed", when this in fact lead to an successful
237 	 * update of the cache.
238 	 */
239 	seq_printf(seq, "\t%s: used:%u/%u hits:%lu misses:%lu starving:%lu locked:%lu changed:%lu\n",
240 		   lc->name, lc->used, lc->nr_elements,
241 		   lc->hits, lc->misses, lc->starving, lc->locked, lc->changed);
242 }
243 
lc_hash_slot(struct lru_cache * lc,unsigned int enr)244 static struct hlist_head *lc_hash_slot(struct lru_cache *lc, unsigned int enr)
245 {
246 	return  lc->lc_slot + (enr % lc->nr_elements);
247 }
248 
249 
__lc_find(struct lru_cache * lc,unsigned int enr,bool include_changing)250 static struct lc_element *__lc_find(struct lru_cache *lc, unsigned int enr,
251 		bool include_changing)
252 {
253 	struct lc_element *e;
254 
255 	BUG_ON(!lc);
256 	BUG_ON(!lc->nr_elements);
257 	hlist_for_each_entry(e, lc_hash_slot(lc, enr), colision) {
258 		/* "about to be changed" elements, pending transaction commit,
259 		 * are hashed by their "new number". "Normal" elements have
260 		 * lc_number == lc_new_number. */
261 		if (e->lc_new_number != enr)
262 			continue;
263 		if (e->lc_new_number == e->lc_number || include_changing)
264 			return e;
265 		break;
266 	}
267 	return NULL;
268 }
269 
270 /**
271  * lc_find - find element by label, if present in the hash table
272  * @lc: The lru_cache object
273  * @enr: element number
274  *
275  * Returns the pointer to an element, if the element with the requested
276  * "label" or element number is present in the hash table,
277  * or NULL if not found. Does not change the refcnt.
278  * Ignores elements that are "about to be used", i.e. not yet in the active
279  * set, but still pending transaction commit.
280  */
lc_find(struct lru_cache * lc,unsigned int enr)281 struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr)
282 {
283 	return __lc_find(lc, enr, 0);
284 }
285 
286 /**
287  * lc_is_used - find element by label
288  * @lc: The lru_cache object
289  * @enr: element number
290  *
291  * Returns true, if the element with the requested "label" or element number is
292  * present in the hash table, and is used (refcnt > 0).
293  * Also finds elements that are not _currently_ used but only "about to be
294  * used", i.e. on the "to_be_changed" list, pending transaction commit.
295  */
lc_is_used(struct lru_cache * lc,unsigned int enr)296 bool lc_is_used(struct lru_cache *lc, unsigned int enr)
297 {
298 	struct lc_element *e = __lc_find(lc, enr, 1);
299 	return e && e->refcnt;
300 }
301 
302 /**
303  * lc_del - removes an element from the cache
304  * @lc: The lru_cache object
305  * @e: The element to remove
306  *
307  * @e must be unused (refcnt == 0). Moves @e from "lru" to "free" list,
308  * sets @e->enr to %LC_FREE.
309  */
lc_del(struct lru_cache * lc,struct lc_element * e)310 void lc_del(struct lru_cache *lc, struct lc_element *e)
311 {
312 	PARANOIA_ENTRY();
313 	PARANOIA_LC_ELEMENT(lc, e);
314 	BUG_ON(e->refcnt);
315 
316 	e->lc_number = e->lc_new_number = LC_FREE;
317 	hlist_del_init(&e->colision);
318 	list_move(&e->list, &lc->free);
319 	RETURN();
320 }
321 
lc_prepare_for_change(struct lru_cache * lc,unsigned new_number)322 static struct lc_element *lc_prepare_for_change(struct lru_cache *lc, unsigned new_number)
323 {
324 	struct list_head *n;
325 	struct lc_element *e;
326 
327 	if (!list_empty(&lc->free))
328 		n = lc->free.next;
329 	else if (!list_empty(&lc->lru))
330 		n = lc->lru.prev;
331 	else
332 		return NULL;
333 
334 	e = list_entry(n, struct lc_element, list);
335 	PARANOIA_LC_ELEMENT(lc, e);
336 
337 	e->lc_new_number = new_number;
338 	if (!hlist_unhashed(&e->colision))
339 		__hlist_del(&e->colision);
340 	hlist_add_head(&e->colision, lc_hash_slot(lc, new_number));
341 	list_move(&e->list, &lc->to_be_changed);
342 
343 	return e;
344 }
345 
lc_unused_element_available(struct lru_cache * lc)346 static int lc_unused_element_available(struct lru_cache *lc)
347 {
348 	if (!list_empty(&lc->free))
349 		return 1; /* something on the free list */
350 	if (!list_empty(&lc->lru))
351 		return 1;  /* something to evict */
352 
353 	return 0;
354 }
355 
356 /* used as internal flags to __lc_get */
357 enum {
358 	LC_GET_MAY_CHANGE = 1,
359 	LC_GET_MAY_USE_UNCOMMITTED = 2,
360 };
361 
__lc_get(struct lru_cache * lc,unsigned int enr,unsigned int flags)362 static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, unsigned int flags)
363 {
364 	struct lc_element *e;
365 
366 	PARANOIA_ENTRY();
367 	if (lc->flags & LC_STARVING) {
368 		++lc->starving;
369 		RETURN(NULL);
370 	}
371 
372 	e = __lc_find(lc, enr, 1);
373 	/* if lc_new_number != lc_number,
374 	 * this enr is currently being pulled in already,
375 	 * and will be available once the pending transaction
376 	 * has been committed. */
377 	if (e) {
378 		if (e->lc_new_number != e->lc_number) {
379 			/* It has been found above, but on the "to_be_changed"
380 			 * list, not yet committed.  Don't pull it in twice,
381 			 * wait for the transaction, then try again...
382 			 */
383 			if (!(flags & LC_GET_MAY_USE_UNCOMMITTED))
384 				RETURN(NULL);
385 			/* ... unless the caller is aware of the implications,
386 			 * probably preparing a cumulative transaction. */
387 			++e->refcnt;
388 			++lc->hits;
389 			RETURN(e);
390 		}
391 		/* else: lc_new_number == lc_number; a real hit. */
392 		++lc->hits;
393 		if (e->refcnt++ == 0)
394 			lc->used++;
395 		list_move(&e->list, &lc->in_use); /* Not evictable... */
396 		RETURN(e);
397 	}
398 	/* e == NULL */
399 
400 	++lc->misses;
401 	if (!(flags & LC_GET_MAY_CHANGE))
402 		RETURN(NULL);
403 
404 	/* To avoid races with lc_try_lock(), first, mark us dirty
405 	 * (using test_and_set_bit, as it implies memory barriers), ... */
406 	test_and_set_bit(__LC_DIRTY, &lc->flags);
407 
408 	/* ... only then check if it is locked anyways. If lc_unlock clears
409 	 * the dirty bit again, that's not a problem, we will come here again.
410 	 */
411 	if (test_bit(__LC_LOCKED, &lc->flags)) {
412 		++lc->locked;
413 		RETURN(NULL);
414 	}
415 
416 	/* In case there is nothing available and we can not kick out
417 	 * the LRU element, we have to wait ...
418 	 */
419 	if (!lc_unused_element_available(lc)) {
420 		__set_bit(__LC_STARVING, &lc->flags);
421 		RETURN(NULL);
422 	}
423 
424 	/* It was not present in the active set.  We are going to recycle an
425 	 * unused (or even "free") element, but we won't accumulate more than
426 	 * max_pending_changes changes.  */
427 	if (lc->pending_changes >= lc->max_pending_changes)
428 		RETURN(NULL);
429 
430 	e = lc_prepare_for_change(lc, enr);
431 	BUG_ON(!e);
432 
433 	clear_bit(__LC_STARVING, &lc->flags);
434 	BUG_ON(++e->refcnt != 1);
435 	lc->used++;
436 	lc->pending_changes++;
437 
438 	RETURN(e);
439 }
440 
441 /**
442  * lc_get - get element by label, maybe change the active set
443  * @lc: the lru cache to operate on
444  * @enr: the label to look up
445  *
446  * Finds an element in the cache, increases its usage count,
447  * "touches" and returns it.
448  *
449  * In case the requested number is not present, it needs to be added to the
450  * cache. Therefore it is possible that an other element becomes evicted from
451  * the cache. In either case, the user is notified so he is able to e.g. keep
452  * a persistent log of the cache changes, and therefore the objects in use.
453  *
454  * Return values:
455  *  NULL
456  *     The cache was marked %LC_STARVING,
457  *     or the requested label was not in the active set
458  *     and a changing transaction is still pending (@lc was marked %LC_DIRTY).
459  *     Or no unused or free element could be recycled (@lc will be marked as
460  *     %LC_STARVING, blocking further lc_get() operations).
461  *
462  *  pointer to the element with the REQUESTED element number.
463  *     In this case, it can be used right away
464  *
465  *  pointer to an UNUSED element with some different element number,
466  *          where that different number may also be %LC_FREE.
467  *
468  *          In this case, the cache is marked %LC_DIRTY,
469  *          so lc_try_lock() will no longer succeed.
470  *          The returned element pointer is moved to the "to_be_changed" list,
471  *          and registered with the new element number on the hash collision chains,
472  *          so it is possible to pick it up from lc_is_used().
473  *          Up to "max_pending_changes" (see lc_create()) can be accumulated.
474  *          The user now should do whatever housekeeping is necessary,
475  *          typically serialize on lc_try_lock_for_transaction(), then call
476  *          lc_committed(lc) and lc_unlock(), to finish the change.
477  *
478  * NOTE: The user needs to check the lc_number on EACH use, so he recognizes
479  *       any cache set change.
480  */
lc_get(struct lru_cache * lc,unsigned int enr)481 struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
482 {
483 	return __lc_get(lc, enr, LC_GET_MAY_CHANGE);
484 }
485 
486 /**
487  * lc_get_cumulative - like lc_get; also finds to-be-changed elements
488  * @lc: the lru cache to operate on
489  * @enr: the label to look up
490  *
491  * Unlike lc_get this also returns the element for @enr, if it is belonging to
492  * a pending transaction, so the return values are like for lc_get(),
493  * plus:
494  *
495  * pointer to an element already on the "to_be_changed" list.
496  * 	In this case, the cache was already marked %LC_DIRTY.
497  *
498  * Caller needs to make sure that the pending transaction is completed,
499  * before proceeding to actually use this element.
500  */
lc_get_cumulative(struct lru_cache * lc,unsigned int enr)501 struct lc_element *lc_get_cumulative(struct lru_cache *lc, unsigned int enr)
502 {
503 	return __lc_get(lc, enr, LC_GET_MAY_CHANGE|LC_GET_MAY_USE_UNCOMMITTED);
504 }
505 
506 /**
507  * lc_try_get - get element by label, if present; do not change the active set
508  * @lc: the lru cache to operate on
509  * @enr: the label to look up
510  *
511  * Finds an element in the cache, increases its usage count,
512  * "touches" and returns it.
513  *
514  * Return values:
515  *  NULL
516  *     The cache was marked %LC_STARVING,
517  *     or the requested label was not in the active set
518  *
519  *  pointer to the element with the REQUESTED element number.
520  *     In this case, it can be used right away
521  */
lc_try_get(struct lru_cache * lc,unsigned int enr)522 struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr)
523 {
524 	return __lc_get(lc, enr, 0);
525 }
526 
527 /**
528  * lc_committed - tell @lc that pending changes have been recorded
529  * @lc: the lru cache to operate on
530  *
531  * User is expected to serialize on explicit lc_try_lock_for_transaction()
532  * before the transaction is started, and later needs to lc_unlock() explicitly
533  * as well.
534  */
lc_committed(struct lru_cache * lc)535 void lc_committed(struct lru_cache *lc)
536 {
537 	struct lc_element *e, *tmp;
538 
539 	PARANOIA_ENTRY();
540 	list_for_each_entry_safe(e, tmp, &lc->to_be_changed, list) {
541 		/* count number of changes, not number of transactions */
542 		++lc->changed;
543 		e->lc_number = e->lc_new_number;
544 		list_move(&e->list, &lc->in_use);
545 	}
546 	lc->pending_changes = 0;
547 	RETURN();
548 }
549 
550 
551 /**
552  * lc_put - give up refcnt of @e
553  * @lc: the lru cache to operate on
554  * @e: the element to put
555  *
556  * If refcnt reaches zero, the element is moved to the lru list,
557  * and a %LC_STARVING (if set) is cleared.
558  * Returns the new (post-decrement) refcnt.
559  */
lc_put(struct lru_cache * lc,struct lc_element * e)560 unsigned int lc_put(struct lru_cache *lc, struct lc_element *e)
561 {
562 	PARANOIA_ENTRY();
563 	PARANOIA_LC_ELEMENT(lc, e);
564 	BUG_ON(e->refcnt == 0);
565 	BUG_ON(e->lc_number != e->lc_new_number);
566 	if (--e->refcnt == 0) {
567 		/* move it to the front of LRU. */
568 		list_move(&e->list, &lc->lru);
569 		lc->used--;
570 		clear_bit_unlock(__LC_STARVING, &lc->flags);
571 	}
572 	RETURN(e->refcnt);
573 }
574 
575 /**
576  * lc_element_by_index
577  * @lc: the lru cache to operate on
578  * @i: the index of the element to return
579  */
lc_element_by_index(struct lru_cache * lc,unsigned i)580 struct lc_element *lc_element_by_index(struct lru_cache *lc, unsigned i)
581 {
582 	BUG_ON(i >= lc->nr_elements);
583 	BUG_ON(lc->lc_element[i] == NULL);
584 	BUG_ON(lc->lc_element[i]->lc_index != i);
585 	return lc->lc_element[i];
586 }
587 
588 /**
589  * lc_index_of
590  * @lc: the lru cache to operate on
591  * @e: the element to query for its index position in lc->element
592  */
lc_index_of(struct lru_cache * lc,struct lc_element * e)593 unsigned int lc_index_of(struct lru_cache *lc, struct lc_element *e)
594 {
595 	PARANOIA_LC_ELEMENT(lc, e);
596 	return e->lc_index;
597 }
598 
599 /**
600  * lc_set - associate index with label
601  * @lc: the lru cache to operate on
602  * @enr: the label to set
603  * @index: the element index to associate label with.
604  *
605  * Used to initialize the active set to some previously recorded state.
606  */
lc_set(struct lru_cache * lc,unsigned int enr,int index)607 void lc_set(struct lru_cache *lc, unsigned int enr, int index)
608 {
609 	struct lc_element *e;
610 	struct list_head *lh;
611 
612 	if (index < 0 || index >= lc->nr_elements)
613 		return;
614 
615 	e = lc_element_by_index(lc, index);
616 	BUG_ON(e->lc_number != e->lc_new_number);
617 	BUG_ON(e->refcnt != 0);
618 
619 	e->lc_number = e->lc_new_number = enr;
620 	hlist_del_init(&e->colision);
621 	if (enr == LC_FREE)
622 		lh = &lc->free;
623 	else {
624 		hlist_add_head(&e->colision, lc_hash_slot(lc, enr));
625 		lh = &lc->lru;
626 	}
627 	list_move(&e->list, lh);
628 }
629 
630 /**
631  * lc_seq_dump_details - Dump a complete LRU cache to seq in textual form.
632  * @lc: the lru cache to operate on
633  * @seq: the &struct seq_file pointer to seq_printf into
634  * @utext: user supplied additional "heading" or other info
635  * @detail: function pointer the user may provide to dump further details
636  * of the object the lc_element is embedded in. May be NULL.
637  * Note: a leading space ' ' and trailing newline '\n' is implied.
638  */
lc_seq_dump_details(struct seq_file * seq,struct lru_cache * lc,char * utext,void (* detail)(struct seq_file *,struct lc_element *))639 void lc_seq_dump_details(struct seq_file *seq, struct lru_cache *lc, char *utext,
640 	     void (*detail) (struct seq_file *, struct lc_element *))
641 {
642 	unsigned int nr_elements = lc->nr_elements;
643 	struct lc_element *e;
644 	int i;
645 
646 	seq_printf(seq, "\tnn: lc_number (new nr) refcnt %s\n ", utext);
647 	for (i = 0; i < nr_elements; i++) {
648 		e = lc_element_by_index(lc, i);
649 		if (e->lc_number != e->lc_new_number)
650 			seq_printf(seq, "\t%5d: %6d %8d %6d ",
651 				i, e->lc_number, e->lc_new_number, e->refcnt);
652 		else
653 			seq_printf(seq, "\t%5d: %6d %-8s %6d ",
654 				i, e->lc_number, "-\"-", e->refcnt);
655 		if (detail)
656 			detail(seq, e);
657 		seq_putc(seq, '\n');
658 	}
659 }
660 
661 EXPORT_SYMBOL(lc_create);
662 EXPORT_SYMBOL(lc_reset);
663 EXPORT_SYMBOL(lc_destroy);
664 EXPORT_SYMBOL(lc_set);
665 EXPORT_SYMBOL(lc_del);
666 EXPORT_SYMBOL(lc_try_get);
667 EXPORT_SYMBOL(lc_find);
668 EXPORT_SYMBOL(lc_get);
669 EXPORT_SYMBOL(lc_put);
670 EXPORT_SYMBOL(lc_committed);
671 EXPORT_SYMBOL(lc_element_by_index);
672 EXPORT_SYMBOL(lc_index_of);
673 EXPORT_SYMBOL(lc_seq_printf_stats);
674 EXPORT_SYMBOL(lc_seq_dump_details);
675 EXPORT_SYMBOL(lc_try_lock);
676 EXPORT_SYMBOL(lc_is_used);
677 EXPORT_SYMBOL(lc_get_cumulative);
678