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TOMOYO Linux Cross Reference
Linux/fs/jbd/revoke.c

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  1 /*
  2  * linux/fs/jbd/revoke.c
  3  *
  4  * Written by Stephen C. Tweedie <sct@redhat.com>, 2000
  5  *
  6  * Copyright 2000 Red Hat corp --- All Rights Reserved
  7  *
  8  * This file is part of the Linux kernel and is made available under
  9  * the terms of the GNU General Public License, version 2, or at your
 10  * option, any later version, incorporated herein by reference.
 11  *
 12  * Journal revoke routines for the generic filesystem journaling code;
 13  * part of the ext2fs journaling system.
 14  *
 15  * Revoke is the mechanism used to prevent old log records for deleted
 16  * metadata from being replayed on top of newer data using the same
 17  * blocks.  The revoke mechanism is used in two separate places:
 18  *
 19  * + Commit: during commit we write the entire list of the current
 20  *   transaction's revoked blocks to the journal
 21  *
 22  * + Recovery: during recovery we record the transaction ID of all
 23  *   revoked blocks.  If there are multiple revoke records in the log
 24  *   for a single block, only the last one counts, and if there is a log
 25  *   entry for a block beyond the last revoke, then that log entry still
 26  *   gets replayed.
 27  *
 28  * We can get interactions between revokes and new log data within a
 29  * single transaction:
 30  *
 31  * Block is revoked and then journaled:
 32  *   The desired end result is the journaling of the new block, so we
 33  *   cancel the revoke before the transaction commits.
 34  *
 35  * Block is journaled and then revoked:
 36  *   The revoke must take precedence over the write of the block, so we
 37  *   need either to cancel the journal entry or to write the revoke
 38  *   later in the log than the log block.  In this case, we choose the
 39  *   latter: journaling a block cancels any revoke record for that block
 40  *   in the current transaction, so any revoke for that block in the
 41  *   transaction must have happened after the block was journaled and so
 42  *   the revoke must take precedence.
 43  *
 44  * Block is revoked and then written as data:
 45  *   The data write is allowed to succeed, but the revoke is _not_
 46  *   cancelled.  We still need to prevent old log records from
 47  *   overwriting the new data.  We don't even need to clear the revoke
 48  *   bit here.
 49  *
 50  * We cache revoke status of a buffer in the current transaction in b_states
 51  * bits.  As the name says, revokevalid flag indicates that the cached revoke
 52  * status of a buffer is valid and we can rely on the cached status.
 53  *
 54  * Revoke information on buffers is a tri-state value:
 55  *
 56  * RevokeValid clear:   no cached revoke status, need to look it up
 57  * RevokeValid set, Revoked clear:
 58  *                      buffer has not been revoked, and cancel_revoke
 59  *                      need do nothing.
 60  * RevokeValid set, Revoked set:
 61  *                      buffer has been revoked.
 62  *
 63  * Locking rules:
 64  * We keep two hash tables of revoke records. One hashtable belongs to the
 65  * running transaction (is pointed to by journal->j_revoke), the other one
 66  * belongs to the committing transaction. Accesses to the second hash table
 67  * happen only from the kjournald and no other thread touches this table.  Also
 68  * journal_switch_revoke_table() which switches which hashtable belongs to the
 69  * running and which to the committing transaction is called only from
 70  * kjournald. Therefore we need no locks when accessing the hashtable belonging
 71  * to the committing transaction.
 72  *
 73  * All users operating on the hash table belonging to the running transaction
 74  * have a handle to the transaction. Therefore they are safe from kjournald
 75  * switching hash tables under them. For operations on the lists of entries in
 76  * the hash table j_revoke_lock is used.
 77  *
 78  * Finally, also replay code uses the hash tables but at this moment no one else
 79  * can touch them (filesystem isn't mounted yet) and hence no locking is
 80  * needed.
 81  */
 82 
 83 #ifndef __KERNEL__
 84 #include "jfs_user.h"
 85 #else
 86 #include <linux/time.h>
 87 #include <linux/fs.h>
 88 #include <linux/jbd.h>
 89 #include <linux/errno.h>
 90 #include <linux/slab.h>
 91 #include <linux/list.h>
 92 #include <linux/init.h>
 93 #include <linux/bio.h>
 94 #endif
 95 #include <linux/log2.h>
 96 
 97 static struct kmem_cache *revoke_record_cache;
 98 static struct kmem_cache *revoke_table_cache;
 99 
100 /* Each revoke record represents one single revoked block.  During
101    journal replay, this involves recording the transaction ID of the
102    last transaction to revoke this block. */
103 
104 struct jbd_revoke_record_s
105 {
106         struct list_head  hash;
107         tid_t             sequence;     /* Used for recovery only */
108         unsigned int      blocknr;
109 };
110 
111 
112 /* The revoke table is just a simple hash table of revoke records. */
113 struct jbd_revoke_table_s
114 {
115         /* It is conceivable that we might want a larger hash table
116          * for recovery.  Must be a power of two. */
117         int               hash_size;
118         int               hash_shift;
119         struct list_head *hash_table;
120 };
121 
122 
123 #ifdef __KERNEL__
124 static void write_one_revoke_record(journal_t *, transaction_t *,
125                                     struct journal_head **, int *,
126                                     struct jbd_revoke_record_s *, int);
127 static void flush_descriptor(journal_t *, struct journal_head *, int, int);
128 #endif
129 
130 /* Utility functions to maintain the revoke table */
131 
132 /* Borrowed from buffer.c: this is a tried and tested block hash function */
133 static inline int hash(journal_t *journal, unsigned int block)
134 {
135         struct jbd_revoke_table_s *table = journal->j_revoke;
136         int hash_shift = table->hash_shift;
137 
138         return ((block << (hash_shift - 6)) ^
139                 (block >> 13) ^
140                 (block << (hash_shift - 12))) & (table->hash_size - 1);
141 }
142 
143 static int insert_revoke_hash(journal_t *journal, unsigned int blocknr,
144                               tid_t seq)
145 {
146         struct list_head *hash_list;
147         struct jbd_revoke_record_s *record;
148 
149 repeat:
150         record = kmem_cache_alloc(revoke_record_cache, GFP_NOFS);
151         if (!record)
152                 goto oom;
153 
154         record->sequence = seq;
155         record->blocknr = blocknr;
156         hash_list = &journal->j_revoke->hash_table[hash(journal, blocknr)];
157         spin_lock(&journal->j_revoke_lock);
158         list_add(&record->hash, hash_list);
159         spin_unlock(&journal->j_revoke_lock);
160         return 0;
161 
162 oom:
163         if (!journal_oom_retry)
164                 return -ENOMEM;
165         jbd_debug(1, "ENOMEM in %s, retrying\n", __func__);
166         yield();
167         goto repeat;
168 }
169 
170 /* Find a revoke record in the journal's hash table. */
171 
172 static struct jbd_revoke_record_s *find_revoke_record(journal_t *journal,
173                                                       unsigned int blocknr)
174 {
175         struct list_head *hash_list;
176         struct jbd_revoke_record_s *record;
177 
178         hash_list = &journal->j_revoke->hash_table[hash(journal, blocknr)];
179 
180         spin_lock(&journal->j_revoke_lock);
181         record = (struct jbd_revoke_record_s *) hash_list->next;
182         while (&(record->hash) != hash_list) {
183                 if (record->blocknr == blocknr) {
184                         spin_unlock(&journal->j_revoke_lock);
185                         return record;
186                 }
187                 record = (struct jbd_revoke_record_s *) record->hash.next;
188         }
189         spin_unlock(&journal->j_revoke_lock);
190         return NULL;
191 }
192 
193 void journal_destroy_revoke_caches(void)
194 {
195         if (revoke_record_cache) {
196                 kmem_cache_destroy(revoke_record_cache);
197                 revoke_record_cache = NULL;
198         }
199         if (revoke_table_cache) {
200                 kmem_cache_destroy(revoke_table_cache);
201                 revoke_table_cache = NULL;
202         }
203 }
204 
205 int __init journal_init_revoke_caches(void)
206 {
207         J_ASSERT(!revoke_record_cache);
208         J_ASSERT(!revoke_table_cache);
209 
210         revoke_record_cache = kmem_cache_create("revoke_record",
211                                            sizeof(struct jbd_revoke_record_s),
212                                            0,
213                                            SLAB_HWCACHE_ALIGN|SLAB_TEMPORARY,
214                                            NULL);
215         if (!revoke_record_cache)
216                 goto record_cache_failure;
217 
218         revoke_table_cache = kmem_cache_create("revoke_table",
219                                            sizeof(struct jbd_revoke_table_s),
220                                            0, SLAB_TEMPORARY, NULL);
221         if (!revoke_table_cache)
222                 goto table_cache_failure;
223 
224         return 0;
225 
226 table_cache_failure:
227         journal_destroy_revoke_caches();
228 record_cache_failure:
229         return -ENOMEM;
230 }
231 
232 static struct jbd_revoke_table_s *journal_init_revoke_table(int hash_size)
233 {
234         int shift = 0;
235         int tmp = hash_size;
236         struct jbd_revoke_table_s *table;
237 
238         table = kmem_cache_alloc(revoke_table_cache, GFP_KERNEL);
239         if (!table)
240                 goto out;
241 
242         while((tmp >>= 1UL) != 0UL)
243                 shift++;
244 
245         table->hash_size = hash_size;
246         table->hash_shift = shift;
247         table->hash_table =
248                 kmalloc(hash_size * sizeof(struct list_head), GFP_KERNEL);
249         if (!table->hash_table) {
250                 kmem_cache_free(revoke_table_cache, table);
251                 table = NULL;
252                 goto out;
253         }
254 
255         for (tmp = 0; tmp < hash_size; tmp++)
256                 INIT_LIST_HEAD(&table->hash_table[tmp]);
257 
258 out:
259         return table;
260 }
261 
262 static void journal_destroy_revoke_table(struct jbd_revoke_table_s *table)
263 {
264         int i;
265         struct list_head *hash_list;
266 
267         for (i = 0; i < table->hash_size; i++) {
268                 hash_list = &table->hash_table[i];
269                 J_ASSERT(list_empty(hash_list));
270         }
271 
272         kfree(table->hash_table);
273         kmem_cache_free(revoke_table_cache, table);
274 }
275 
276 /* Initialise the revoke table for a given journal to a given size. */
277 int journal_init_revoke(journal_t *journal, int hash_size)
278 {
279         J_ASSERT(journal->j_revoke_table[0] == NULL);
280         J_ASSERT(is_power_of_2(hash_size));
281 
282         journal->j_revoke_table[0] = journal_init_revoke_table(hash_size);
283         if (!journal->j_revoke_table[0])
284                 goto fail0;
285 
286         journal->j_revoke_table[1] = journal_init_revoke_table(hash_size);
287         if (!journal->j_revoke_table[1])
288                 goto fail1;
289 
290         journal->j_revoke = journal->j_revoke_table[1];
291 
292         spin_lock_init(&journal->j_revoke_lock);
293 
294         return 0;
295 
296 fail1:
297         journal_destroy_revoke_table(journal->j_revoke_table[0]);
298 fail0:
299         return -ENOMEM;
300 }
301 
302 /* Destroy a journal's revoke table.  The table must already be empty! */
303 void journal_destroy_revoke(journal_t *journal)
304 {
305         journal->j_revoke = NULL;
306         if (journal->j_revoke_table[0])
307                 journal_destroy_revoke_table(journal->j_revoke_table[0]);
308         if (journal->j_revoke_table[1])
309                 journal_destroy_revoke_table(journal->j_revoke_table[1]);
310 }
311 
312 
313 #ifdef __KERNEL__
314 
315 /*
316  * journal_revoke: revoke a given buffer_head from the journal.  This
317  * prevents the block from being replayed during recovery if we take a
318  * crash after this current transaction commits.  Any subsequent
319  * metadata writes of the buffer in this transaction cancel the
320  * revoke.
321  *
322  * Note that this call may block --- it is up to the caller to make
323  * sure that there are no further calls to journal_write_metadata
324  * before the revoke is complete.  In ext3, this implies calling the
325  * revoke before clearing the block bitmap when we are deleting
326  * metadata.
327  *
328  * Revoke performs a journal_forget on any buffer_head passed in as a
329  * parameter, but does _not_ forget the buffer_head if the bh was only
330  * found implicitly.
331  *
332  * bh_in may not be a journalled buffer - it may have come off
333  * the hash tables without an attached journal_head.
334  *
335  * If bh_in is non-zero, journal_revoke() will decrement its b_count
336  * by one.
337  */
338 
339 int journal_revoke(handle_t *handle, unsigned int blocknr,
340                    struct buffer_head *bh_in)
341 {
342         struct buffer_head *bh = NULL;
343         journal_t *journal;
344         struct block_device *bdev;
345         int err;
346 
347         might_sleep();
348         if (bh_in)
349                 BUFFER_TRACE(bh_in, "enter");
350 
351         journal = handle->h_transaction->t_journal;
352         if (!journal_set_features(journal, 0, 0, JFS_FEATURE_INCOMPAT_REVOKE)){
353                 J_ASSERT (!"Cannot set revoke feature!");
354                 return -EINVAL;
355         }
356 
357         bdev = journal->j_fs_dev;
358         bh = bh_in;
359 
360         if (!bh) {
361                 bh = __find_get_block(bdev, blocknr, journal->j_blocksize);
362                 if (bh)
363                         BUFFER_TRACE(bh, "found on hash");
364         }
365 #ifdef JBD_EXPENSIVE_CHECKING
366         else {
367                 struct buffer_head *bh2;
368 
369                 /* If there is a different buffer_head lying around in
370                  * memory anywhere... */
371                 bh2 = __find_get_block(bdev, blocknr, journal->j_blocksize);
372                 if (bh2) {
373                         /* ... and it has RevokeValid status... */
374                         if (bh2 != bh && buffer_revokevalid(bh2))
375                                 /* ...then it better be revoked too,
376                                  * since it's illegal to create a revoke
377                                  * record against a buffer_head which is
378                                  * not marked revoked --- that would
379                                  * risk missing a subsequent revoke
380                                  * cancel. */
381                                 J_ASSERT_BH(bh2, buffer_revoked(bh2));
382                         put_bh(bh2);
383                 }
384         }
385 #endif
386 
387         /* We really ought not ever to revoke twice in a row without
388            first having the revoke cancelled: it's illegal to free a
389            block twice without allocating it in between! */
390         if (bh) {
391                 if (!J_EXPECT_BH(bh, !buffer_revoked(bh),
392                                  "inconsistent data on disk")) {
393                         if (!bh_in)
394                                 brelse(bh);
395                         return -EIO;
396                 }
397                 set_buffer_revoked(bh);
398                 set_buffer_revokevalid(bh);
399                 if (bh_in) {
400                         BUFFER_TRACE(bh_in, "call journal_forget");
401                         journal_forget(handle, bh_in);
402                 } else {
403                         BUFFER_TRACE(bh, "call brelse");
404                         __brelse(bh);
405                 }
406         }
407 
408         jbd_debug(2, "insert revoke for block %u, bh_in=%p\n", blocknr, bh_in);
409         err = insert_revoke_hash(journal, blocknr,
410                                 handle->h_transaction->t_tid);
411         BUFFER_TRACE(bh_in, "exit");
412         return err;
413 }
414 
415 /*
416  * Cancel an outstanding revoke.  For use only internally by the
417  * journaling code (called from journal_get_write_access).
418  *
419  * We trust buffer_revoked() on the buffer if the buffer is already
420  * being journaled: if there is no revoke pending on the buffer, then we
421  * don't do anything here.
422  *
423  * This would break if it were possible for a buffer to be revoked and
424  * discarded, and then reallocated within the same transaction.  In such
425  * a case we would have lost the revoked bit, but when we arrived here
426  * the second time we would still have a pending revoke to cancel.  So,
427  * do not trust the Revoked bit on buffers unless RevokeValid is also
428  * set.
429  */
430 int journal_cancel_revoke(handle_t *handle, struct journal_head *jh)
431 {
432         struct jbd_revoke_record_s *record;
433         journal_t *journal = handle->h_transaction->t_journal;
434         int need_cancel;
435         int did_revoke = 0;     /* akpm: debug */
436         struct buffer_head *bh = jh2bh(jh);
437 
438         jbd_debug(4, "journal_head %p, cancelling revoke\n", jh);
439 
440         /* Is the existing Revoke bit valid?  If so, we trust it, and
441          * only perform the full cancel if the revoke bit is set.  If
442          * not, we can't trust the revoke bit, and we need to do the
443          * full search for a revoke record. */
444         if (test_set_buffer_revokevalid(bh)) {
445                 need_cancel = test_clear_buffer_revoked(bh);
446         } else {
447                 need_cancel = 1;
448                 clear_buffer_revoked(bh);
449         }
450 
451         if (need_cancel) {
452                 record = find_revoke_record(journal, bh->b_blocknr);
453                 if (record) {
454                         jbd_debug(4, "cancelled existing revoke on "
455                                   "blocknr %llu\n", (unsigned long long)bh->b_blocknr);
456                         spin_lock(&journal->j_revoke_lock);
457                         list_del(&record->hash);
458                         spin_unlock(&journal->j_revoke_lock);
459                         kmem_cache_free(revoke_record_cache, record);
460                         did_revoke = 1;
461                 }
462         }
463 
464 #ifdef JBD_EXPENSIVE_CHECKING
465         /* There better not be one left behind by now! */
466         record = find_revoke_record(journal, bh->b_blocknr);
467         J_ASSERT_JH(jh, record == NULL);
468 #endif
469 
470         /* Finally, have we just cleared revoke on an unhashed
471          * buffer_head?  If so, we'd better make sure we clear the
472          * revoked status on any hashed alias too, otherwise the revoke
473          * state machine will get very upset later on. */
474         if (need_cancel) {
475                 struct buffer_head *bh2;
476                 bh2 = __find_get_block(bh->b_bdev, bh->b_blocknr, bh->b_size);
477                 if (bh2) {
478                         if (bh2 != bh)
479                                 clear_buffer_revoked(bh2);
480                         __brelse(bh2);
481                 }
482         }
483         return did_revoke;
484 }
485 
486 /*
487  * journal_clear_revoked_flags clears revoked flag of buffers in
488  * revoke table to reflect there is no revoked buffer in the next
489  * transaction which is going to be started.
490  */
491 void journal_clear_buffer_revoked_flags(journal_t *journal)
492 {
493         struct jbd_revoke_table_s *revoke = journal->j_revoke;
494         int i = 0;
495 
496         for (i = 0; i < revoke->hash_size; i++) {
497                 struct list_head *hash_list;
498                 struct list_head *list_entry;
499                 hash_list = &revoke->hash_table[i];
500 
501                 list_for_each(list_entry, hash_list) {
502                         struct jbd_revoke_record_s *record;
503                         struct buffer_head *bh;
504                         record = (struct jbd_revoke_record_s *)list_entry;
505                         bh = __find_get_block(journal->j_fs_dev,
506                                               record->blocknr,
507                                               journal->j_blocksize);
508                         if (bh) {
509                                 clear_buffer_revoked(bh);
510                                 __brelse(bh);
511                         }
512                 }
513         }
514 }
515 
516 /* journal_switch_revoke table select j_revoke for next transaction
517  * we do not want to suspend any processing until all revokes are
518  * written -bzzz
519  */
520 void journal_switch_revoke_table(journal_t *journal)
521 {
522         int i;
523 
524         if (journal->j_revoke == journal->j_revoke_table[0])
525                 journal->j_revoke = journal->j_revoke_table[1];
526         else
527                 journal->j_revoke = journal->j_revoke_table[0];
528 
529         for (i = 0; i < journal->j_revoke->hash_size; i++)
530                 INIT_LIST_HEAD(&journal->j_revoke->hash_table[i]);
531 }
532 
533 /*
534  * Write revoke records to the journal for all entries in the current
535  * revoke hash, deleting the entries as we go.
536  */
537 void journal_write_revoke_records(journal_t *journal,
538                                   transaction_t *transaction, int write_op)
539 {
540         struct journal_head *descriptor;
541         struct jbd_revoke_record_s *record;
542         struct jbd_revoke_table_s *revoke;
543         struct list_head *hash_list;
544         int i, offset, count;
545 
546         descriptor = NULL;
547         offset = 0;
548         count = 0;
549 
550         /* select revoke table for committing transaction */
551         revoke = journal->j_revoke == journal->j_revoke_table[0] ?
552                 journal->j_revoke_table[1] : journal->j_revoke_table[0];
553 
554         for (i = 0; i < revoke->hash_size; i++) {
555                 hash_list = &revoke->hash_table[i];
556 
557                 while (!list_empty(hash_list)) {
558                         record = (struct jbd_revoke_record_s *)
559                                 hash_list->next;
560                         write_one_revoke_record(journal, transaction,
561                                                 &descriptor, &offset,
562                                                 record, write_op);
563                         count++;
564                         list_del(&record->hash);
565                         kmem_cache_free(revoke_record_cache, record);
566                 }
567         }
568         if (descriptor)
569                 flush_descriptor(journal, descriptor, offset, write_op);
570         jbd_debug(1, "Wrote %d revoke records\n", count);
571 }
572 
573 /*
574  * Write out one revoke record.  We need to create a new descriptor
575  * block if the old one is full or if we have not already created one.
576  */
577 
578 static void write_one_revoke_record(journal_t *journal,
579                                     transaction_t *transaction,
580                                     struct journal_head **descriptorp,
581                                     int *offsetp,
582                                     struct jbd_revoke_record_s *record,
583                                     int write_op)
584 {
585         struct journal_head *descriptor;
586         int offset;
587         journal_header_t *header;
588 
589         /* If we are already aborting, this all becomes a noop.  We
590            still need to go round the loop in
591            journal_write_revoke_records in order to free all of the
592            revoke records: only the IO to the journal is omitted. */
593         if (is_journal_aborted(journal))
594                 return;
595 
596         descriptor = *descriptorp;
597         offset = *offsetp;
598 
599         /* Make sure we have a descriptor with space left for the record */
600         if (descriptor) {
601                 if (offset == journal->j_blocksize) {
602                         flush_descriptor(journal, descriptor, offset, write_op);
603                         descriptor = NULL;
604                 }
605         }
606 
607         if (!descriptor) {
608                 descriptor = journal_get_descriptor_buffer(journal);
609                 if (!descriptor)
610                         return;
611                 header = (journal_header_t *) &jh2bh(descriptor)->b_data[0];
612                 header->h_magic     = cpu_to_be32(JFS_MAGIC_NUMBER);
613                 header->h_blocktype = cpu_to_be32(JFS_REVOKE_BLOCK);
614                 header->h_sequence  = cpu_to_be32(transaction->t_tid);
615 
616                 /* Record it so that we can wait for IO completion later */
617                 JBUFFER_TRACE(descriptor, "file as BJ_LogCtl");
618                 journal_file_buffer(descriptor, transaction, BJ_LogCtl);
619 
620                 offset = sizeof(journal_revoke_header_t);
621                 *descriptorp = descriptor;
622         }
623 
624         * ((__be32 *)(&jh2bh(descriptor)->b_data[offset])) =
625                 cpu_to_be32(record->blocknr);
626         offset += 4;
627         *offsetp = offset;
628 }
629 
630 /*
631  * Flush a revoke descriptor out to the journal.  If we are aborting,
632  * this is a noop; otherwise we are generating a buffer which needs to
633  * be waited for during commit, so it has to go onto the appropriate
634  * journal buffer list.
635  */
636 
637 static void flush_descriptor(journal_t *journal,
638                              struct journal_head *descriptor,
639                              int offset, int write_op)
640 {
641         journal_revoke_header_t *header;
642         struct buffer_head *bh = jh2bh(descriptor);
643 
644         if (is_journal_aborted(journal)) {
645                 put_bh(bh);
646                 return;
647         }
648 
649         header = (journal_revoke_header_t *) jh2bh(descriptor)->b_data;
650         header->r_count = cpu_to_be32(offset);
651         set_buffer_jwrite(bh);
652         BUFFER_TRACE(bh, "write");
653         set_buffer_dirty(bh);
654         write_dirty_buffer(bh, write_op);
655 }
656 #endif
657 
658 /*
659  * Revoke support for recovery.
660  *
661  * Recovery needs to be able to:
662  *
663  *  record all revoke records, including the tid of the latest instance
664  *  of each revoke in the journal
665  *
666  *  check whether a given block in a given transaction should be replayed
667  *  (ie. has not been revoked by a revoke record in that or a subsequent
668  *  transaction)
669  *
670  *  empty the revoke table after recovery.
671  */
672 
673 /*
674  * First, setting revoke records.  We create a new revoke record for
675  * every block ever revoked in the log as we scan it for recovery, and
676  * we update the existing records if we find multiple revokes for a
677  * single block.
678  */
679 
680 int journal_set_revoke(journal_t *journal,
681                        unsigned int blocknr,
682                        tid_t sequence)
683 {
684         struct jbd_revoke_record_s *record;
685 
686         record = find_revoke_record(journal, blocknr);
687         if (record) {
688                 /* If we have multiple occurrences, only record the
689                  * latest sequence number in the hashed record */
690                 if (tid_gt(sequence, record->sequence))
691                         record->sequence = sequence;
692                 return 0;
693         }
694         return insert_revoke_hash(journal, blocknr, sequence);
695 }
696 
697 /*
698  * Test revoke records.  For a given block referenced in the log, has
699  * that block been revoked?  A revoke record with a given transaction
700  * sequence number revokes all blocks in that transaction and earlier
701  * ones, but later transactions still need replayed.
702  */
703 
704 int journal_test_revoke(journal_t *journal,
705                         unsigned int blocknr,
706                         tid_t sequence)
707 {
708         struct jbd_revoke_record_s *record;
709 
710         record = find_revoke_record(journal, blocknr);
711         if (!record)
712                 return 0;
713         if (tid_gt(sequence, record->sequence))
714                 return 0;
715         return 1;
716 }
717 
718 /*
719  * Finally, once recovery is over, we need to clear the revoke table so
720  * that it can be reused by the running filesystem.
721  */
722 
723 void journal_clear_revoke(journal_t *journal)
724 {
725         int i;
726         struct list_head *hash_list;
727         struct jbd_revoke_record_s *record;
728         struct jbd_revoke_table_s *revoke;
729 
730         revoke = journal->j_revoke;
731 
732         for (i = 0; i < revoke->hash_size; i++) {
733                 hash_list = &revoke->hash_table[i];
734                 while (!list_empty(hash_list)) {
735                         record = (struct jbd_revoke_record_s*) hash_list->next;
736                         list_del(&record->hash);
737                         kmem_cache_free(revoke_record_cache, record);
738                 }
739         }
740 }
741 

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