xref: /openbmc/linux/fs/jbd2/revoke.c (revision e553d2a5)
1  // SPDX-License-Identifier: GPL-2.0+
2  /*
3   * linux/fs/jbd2/revoke.c
4   *
5   * Written by Stephen C. Tweedie <sct@redhat.com>, 2000
6   *
7   * Copyright 2000 Red Hat corp --- All Rights Reserved
8   *
9   * Journal revoke routines for the generic filesystem journaling code;
10   * part of the ext2fs journaling system.
11   *
12   * Revoke is the mechanism used to prevent old log records for deleted
13   * metadata from being replayed on top of newer data using the same
14   * blocks.  The revoke mechanism is used in two separate places:
15   *
16   * + Commit: during commit we write the entire list of the current
17   *   transaction's revoked blocks to the journal
18   *
19   * + Recovery: during recovery we record the transaction ID of all
20   *   revoked blocks.  If there are multiple revoke records in the log
21   *   for a single block, only the last one counts, and if there is a log
22   *   entry for a block beyond the last revoke, then that log entry still
23   *   gets replayed.
24   *
25   * We can get interactions between revokes and new log data within a
26   * single transaction:
27   *
28   * Block is revoked and then journaled:
29   *   The desired end result is the journaling of the new block, so we
30   *   cancel the revoke before the transaction commits.
31   *
32   * Block is journaled and then revoked:
33   *   The revoke must take precedence over the write of the block, so we
34   *   need either to cancel the journal entry or to write the revoke
35   *   later in the log than the log block.  In this case, we choose the
36   *   latter: journaling a block cancels any revoke record for that block
37   *   in the current transaction, so any revoke for that block in the
38   *   transaction must have happened after the block was journaled and so
39   *   the revoke must take precedence.
40   *
41   * Block is revoked and then written as data:
42   *   The data write is allowed to succeed, but the revoke is _not_
43   *   cancelled.  We still need to prevent old log records from
44   *   overwriting the new data.  We don't even need to clear the revoke
45   *   bit here.
46   *
47   * We cache revoke status of a buffer in the current transaction in b_states
48   * bits.  As the name says, revokevalid flag indicates that the cached revoke
49   * status of a buffer is valid and we can rely on the cached status.
50   *
51   * Revoke information on buffers is a tri-state value:
52   *
53   * RevokeValid clear:	no cached revoke status, need to look it up
54   * RevokeValid set, Revoked clear:
55   *			buffer has not been revoked, and cancel_revoke
56   *			need do nothing.
57   * RevokeValid set, Revoked set:
58   *			buffer has been revoked.
59   *
60   * Locking rules:
61   * We keep two hash tables of revoke records. One hashtable belongs to the
62   * running transaction (is pointed to by journal->j_revoke), the other one
63   * belongs to the committing transaction. Accesses to the second hash table
64   * happen only from the kjournald and no other thread touches this table.  Also
65   * journal_switch_revoke_table() which switches which hashtable belongs to the
66   * running and which to the committing transaction is called only from
67   * kjournald. Therefore we need no locks when accessing the hashtable belonging
68   * to the committing transaction.
69   *
70   * All users operating on the hash table belonging to the running transaction
71   * have a handle to the transaction. Therefore they are safe from kjournald
72   * switching hash tables under them. For operations on the lists of entries in
73   * the hash table j_revoke_lock is used.
74   *
75   * Finally, also replay code uses the hash tables but at this moment no one else
76   * can touch them (filesystem isn't mounted yet) and hence no locking is
77   * needed.
78   */
79  
80  #ifndef __KERNEL__
81  #include "jfs_user.h"
82  #else
83  #include <linux/time.h>
84  #include <linux/fs.h>
85  #include <linux/jbd2.h>
86  #include <linux/errno.h>
87  #include <linux/slab.h>
88  #include <linux/list.h>
89  #include <linux/init.h>
90  #include <linux/bio.h>
91  #include <linux/log2.h>
92  #include <linux/hash.h>
93  #endif
94  
95  static struct kmem_cache *jbd2_revoke_record_cache;
96  static struct kmem_cache *jbd2_revoke_table_cache;
97  
98  /* Each revoke record represents one single revoked block.  During
99     journal replay, this involves recording the transaction ID of the
100     last transaction to revoke this block. */
101  
102  struct jbd2_revoke_record_s
103  {
104  	struct list_head  hash;
105  	tid_t		  sequence;	/* Used for recovery only */
106  	unsigned long long	  blocknr;
107  };
108  
109  
110  /* The revoke table is just a simple hash table of revoke records. */
111  struct jbd2_revoke_table_s
112  {
113  	/* It is conceivable that we might want a larger hash table
114  	 * for recovery.  Must be a power of two. */
115  	int		  hash_size;
116  	int		  hash_shift;
117  	struct list_head *hash_table;
118  };
119  
120  
121  #ifdef __KERNEL__
122  static void write_one_revoke_record(transaction_t *,
123  				    struct list_head *,
124  				    struct buffer_head **, int *,
125  				    struct jbd2_revoke_record_s *);
126  static void flush_descriptor(journal_t *, struct buffer_head *, int);
127  #endif
128  
129  /* Utility functions to maintain the revoke table */
130  
131  static inline int hash(journal_t *journal, unsigned long long block)
132  {
133  	return hash_64(block, journal->j_revoke->hash_shift);
134  }
135  
136  static int insert_revoke_hash(journal_t *journal, unsigned long long blocknr,
137  			      tid_t seq)
138  {
139  	struct list_head *hash_list;
140  	struct jbd2_revoke_record_s *record;
141  	gfp_t gfp_mask = GFP_NOFS;
142  
143  	if (journal_oom_retry)
144  		gfp_mask |= __GFP_NOFAIL;
145  	record = kmem_cache_alloc(jbd2_revoke_record_cache, gfp_mask);
146  	if (!record)
147  		return -ENOMEM;
148  
149  	record->sequence = seq;
150  	record->blocknr = blocknr;
151  	hash_list = &journal->j_revoke->hash_table[hash(journal, blocknr)];
152  	spin_lock(&journal->j_revoke_lock);
153  	list_add(&record->hash, hash_list);
154  	spin_unlock(&journal->j_revoke_lock);
155  	return 0;
156  }
157  
158  /* Find a revoke record in the journal's hash table. */
159  
160  static struct jbd2_revoke_record_s *find_revoke_record(journal_t *journal,
161  						      unsigned long long blocknr)
162  {
163  	struct list_head *hash_list;
164  	struct jbd2_revoke_record_s *record;
165  
166  	hash_list = &journal->j_revoke->hash_table[hash(journal, blocknr)];
167  
168  	spin_lock(&journal->j_revoke_lock);
169  	record = (struct jbd2_revoke_record_s *) hash_list->next;
170  	while (&(record->hash) != hash_list) {
171  		if (record->blocknr == blocknr) {
172  			spin_unlock(&journal->j_revoke_lock);
173  			return record;
174  		}
175  		record = (struct jbd2_revoke_record_s *) record->hash.next;
176  	}
177  	spin_unlock(&journal->j_revoke_lock);
178  	return NULL;
179  }
180  
181  void jbd2_journal_destroy_revoke_record_cache(void)
182  {
183  	kmem_cache_destroy(jbd2_revoke_record_cache);
184  	jbd2_revoke_record_cache = NULL;
185  }
186  
187  void jbd2_journal_destroy_revoke_table_cache(void)
188  {
189  	kmem_cache_destroy(jbd2_revoke_table_cache);
190  	jbd2_revoke_table_cache = NULL;
191  }
192  
193  int __init jbd2_journal_init_revoke_record_cache(void)
194  {
195  	J_ASSERT(!jbd2_revoke_record_cache);
196  	jbd2_revoke_record_cache = KMEM_CACHE(jbd2_revoke_record_s,
197  					SLAB_HWCACHE_ALIGN|SLAB_TEMPORARY);
198  
199  	if (!jbd2_revoke_record_cache) {
200  		pr_emerg("JBD2: failed to create revoke_record cache\n");
201  		return -ENOMEM;
202  	}
203  	return 0;
204  }
205  
206  int __init jbd2_journal_init_revoke_table_cache(void)
207  {
208  	J_ASSERT(!jbd2_revoke_table_cache);
209  	jbd2_revoke_table_cache = KMEM_CACHE(jbd2_revoke_table_s,
210  					     SLAB_TEMPORARY);
211  	if (!jbd2_revoke_table_cache) {
212  		pr_emerg("JBD2: failed to create revoke_table cache\n");
213  		return -ENOMEM;
214  	}
215  	return 0;
216  }
217  
218  static struct jbd2_revoke_table_s *jbd2_journal_init_revoke_table(int hash_size)
219  {
220  	int shift = 0;
221  	int tmp = hash_size;
222  	struct jbd2_revoke_table_s *table;
223  
224  	table = kmem_cache_alloc(jbd2_revoke_table_cache, GFP_KERNEL);
225  	if (!table)
226  		goto out;
227  
228  	while((tmp >>= 1UL) != 0UL)
229  		shift++;
230  
231  	table->hash_size = hash_size;
232  	table->hash_shift = shift;
233  	table->hash_table =
234  		kmalloc_array(hash_size, sizeof(struct list_head), GFP_KERNEL);
235  	if (!table->hash_table) {
236  		kmem_cache_free(jbd2_revoke_table_cache, table);
237  		table = NULL;
238  		goto out;
239  	}
240  
241  	for (tmp = 0; tmp < hash_size; tmp++)
242  		INIT_LIST_HEAD(&table->hash_table[tmp]);
243  
244  out:
245  	return table;
246  }
247  
248  static void jbd2_journal_destroy_revoke_table(struct jbd2_revoke_table_s *table)
249  {
250  	int i;
251  	struct list_head *hash_list;
252  
253  	for (i = 0; i < table->hash_size; i++) {
254  		hash_list = &table->hash_table[i];
255  		J_ASSERT(list_empty(hash_list));
256  	}
257  
258  	kfree(table->hash_table);
259  	kmem_cache_free(jbd2_revoke_table_cache, table);
260  }
261  
262  /* Initialise the revoke table for a given journal to a given size. */
263  int jbd2_journal_init_revoke(journal_t *journal, int hash_size)
264  {
265  	J_ASSERT(journal->j_revoke_table[0] == NULL);
266  	J_ASSERT(is_power_of_2(hash_size));
267  
268  	journal->j_revoke_table[0] = jbd2_journal_init_revoke_table(hash_size);
269  	if (!journal->j_revoke_table[0])
270  		goto fail0;
271  
272  	journal->j_revoke_table[1] = jbd2_journal_init_revoke_table(hash_size);
273  	if (!journal->j_revoke_table[1])
274  		goto fail1;
275  
276  	journal->j_revoke = journal->j_revoke_table[1];
277  
278  	spin_lock_init(&journal->j_revoke_lock);
279  
280  	return 0;
281  
282  fail1:
283  	jbd2_journal_destroy_revoke_table(journal->j_revoke_table[0]);
284  	journal->j_revoke_table[0] = NULL;
285  fail0:
286  	return -ENOMEM;
287  }
288  
289  /* Destroy a journal's revoke table.  The table must already be empty! */
290  void jbd2_journal_destroy_revoke(journal_t *journal)
291  {
292  	journal->j_revoke = NULL;
293  	if (journal->j_revoke_table[0])
294  		jbd2_journal_destroy_revoke_table(journal->j_revoke_table[0]);
295  	if (journal->j_revoke_table[1])
296  		jbd2_journal_destroy_revoke_table(journal->j_revoke_table[1]);
297  }
298  
299  
300  #ifdef __KERNEL__
301  
302  /*
303   * jbd2_journal_revoke: revoke a given buffer_head from the journal.  This
304   * prevents the block from being replayed during recovery if we take a
305   * crash after this current transaction commits.  Any subsequent
306   * metadata writes of the buffer in this transaction cancel the
307   * revoke.
308   *
309   * Note that this call may block --- it is up to the caller to make
310   * sure that there are no further calls to journal_write_metadata
311   * before the revoke is complete.  In ext3, this implies calling the
312   * revoke before clearing the block bitmap when we are deleting
313   * metadata.
314   *
315   * Revoke performs a jbd2_journal_forget on any buffer_head passed in as a
316   * parameter, but does _not_ forget the buffer_head if the bh was only
317   * found implicitly.
318   *
319   * bh_in may not be a journalled buffer - it may have come off
320   * the hash tables without an attached journal_head.
321   *
322   * If bh_in is non-zero, jbd2_journal_revoke() will decrement its b_count
323   * by one.
324   */
325  
326  int jbd2_journal_revoke(handle_t *handle, unsigned long long blocknr,
327  		   struct buffer_head *bh_in)
328  {
329  	struct buffer_head *bh = NULL;
330  	journal_t *journal;
331  	struct block_device *bdev;
332  	int err;
333  
334  	might_sleep();
335  	if (bh_in)
336  		BUFFER_TRACE(bh_in, "enter");
337  
338  	journal = handle->h_transaction->t_journal;
339  	if (!jbd2_journal_set_features(journal, 0, 0, JBD2_FEATURE_INCOMPAT_REVOKE)){
340  		J_ASSERT (!"Cannot set revoke feature!");
341  		return -EINVAL;
342  	}
343  
344  	bdev = journal->j_fs_dev;
345  	bh = bh_in;
346  
347  	if (!bh) {
348  		bh = __find_get_block(bdev, blocknr, journal->j_blocksize);
349  		if (bh)
350  			BUFFER_TRACE(bh, "found on hash");
351  	}
352  #ifdef JBD2_EXPENSIVE_CHECKING
353  	else {
354  		struct buffer_head *bh2;
355  
356  		/* If there is a different buffer_head lying around in
357  		 * memory anywhere... */
358  		bh2 = __find_get_block(bdev, blocknr, journal->j_blocksize);
359  		if (bh2) {
360  			/* ... and it has RevokeValid status... */
361  			if (bh2 != bh && buffer_revokevalid(bh2))
362  				/* ...then it better be revoked too,
363  				 * since it's illegal to create a revoke
364  				 * record against a buffer_head which is
365  				 * not marked revoked --- that would
366  				 * risk missing a subsequent revoke
367  				 * cancel. */
368  				J_ASSERT_BH(bh2, buffer_revoked(bh2));
369  			put_bh(bh2);
370  		}
371  	}
372  #endif
373  
374  	/* We really ought not ever to revoke twice in a row without
375             first having the revoke cancelled: it's illegal to free a
376             block twice without allocating it in between! */
377  	if (bh) {
378  		if (!J_EXPECT_BH(bh, !buffer_revoked(bh),
379  				 "inconsistent data on disk")) {
380  			if (!bh_in)
381  				brelse(bh);
382  			return -EIO;
383  		}
384  		set_buffer_revoked(bh);
385  		set_buffer_revokevalid(bh);
386  		if (bh_in) {
387  			BUFFER_TRACE(bh_in, "call jbd2_journal_forget");
388  			jbd2_journal_forget(handle, bh_in);
389  		} else {
390  			BUFFER_TRACE(bh, "call brelse");
391  			__brelse(bh);
392  		}
393  	}
394  
395  	jbd_debug(2, "insert revoke for block %llu, bh_in=%p\n",blocknr, bh_in);
396  	err = insert_revoke_hash(journal, blocknr,
397  				handle->h_transaction->t_tid);
398  	BUFFER_TRACE(bh_in, "exit");
399  	return err;
400  }
401  
402  /*
403   * Cancel an outstanding revoke.  For use only internally by the
404   * journaling code (called from jbd2_journal_get_write_access).
405   *
406   * We trust buffer_revoked() on the buffer if the buffer is already
407   * being journaled: if there is no revoke pending on the buffer, then we
408   * don't do anything here.
409   *
410   * This would break if it were possible for a buffer to be revoked and
411   * discarded, and then reallocated within the same transaction.  In such
412   * a case we would have lost the revoked bit, but when we arrived here
413   * the second time we would still have a pending revoke to cancel.  So,
414   * do not trust the Revoked bit on buffers unless RevokeValid is also
415   * set.
416   */
417  int jbd2_journal_cancel_revoke(handle_t *handle, struct journal_head *jh)
418  {
419  	struct jbd2_revoke_record_s *record;
420  	journal_t *journal = handle->h_transaction->t_journal;
421  	int need_cancel;
422  	int did_revoke = 0;	/* akpm: debug */
423  	struct buffer_head *bh = jh2bh(jh);
424  
425  	jbd_debug(4, "journal_head %p, cancelling revoke\n", jh);
426  
427  	/* Is the existing Revoke bit valid?  If so, we trust it, and
428  	 * only perform the full cancel if the revoke bit is set.  If
429  	 * not, we can't trust the revoke bit, and we need to do the
430  	 * full search for a revoke record. */
431  	if (test_set_buffer_revokevalid(bh)) {
432  		need_cancel = test_clear_buffer_revoked(bh);
433  	} else {
434  		need_cancel = 1;
435  		clear_buffer_revoked(bh);
436  	}
437  
438  	if (need_cancel) {
439  		record = find_revoke_record(journal, bh->b_blocknr);
440  		if (record) {
441  			jbd_debug(4, "cancelled existing revoke on "
442  				  "blocknr %llu\n", (unsigned long long)bh->b_blocknr);
443  			spin_lock(&journal->j_revoke_lock);
444  			list_del(&record->hash);
445  			spin_unlock(&journal->j_revoke_lock);
446  			kmem_cache_free(jbd2_revoke_record_cache, record);
447  			did_revoke = 1;
448  		}
449  	}
450  
451  #ifdef JBD2_EXPENSIVE_CHECKING
452  	/* There better not be one left behind by now! */
453  	record = find_revoke_record(journal, bh->b_blocknr);
454  	J_ASSERT_JH(jh, record == NULL);
455  #endif
456  
457  	/* Finally, have we just cleared revoke on an unhashed
458  	 * buffer_head?  If so, we'd better make sure we clear the
459  	 * revoked status on any hashed alias too, otherwise the revoke
460  	 * state machine will get very upset later on. */
461  	if (need_cancel) {
462  		struct buffer_head *bh2;
463  		bh2 = __find_get_block(bh->b_bdev, bh->b_blocknr, bh->b_size);
464  		if (bh2) {
465  			if (bh2 != bh)
466  				clear_buffer_revoked(bh2);
467  			__brelse(bh2);
468  		}
469  	}
470  	return did_revoke;
471  }
472  
473  /*
474   * journal_clear_revoked_flag clears revoked flag of buffers in
475   * revoke table to reflect there is no revoked buffers in the next
476   * transaction which is going to be started.
477   */
478  void jbd2_clear_buffer_revoked_flags(journal_t *journal)
479  {
480  	struct jbd2_revoke_table_s *revoke = journal->j_revoke;
481  	int i = 0;
482  
483  	for (i = 0; i < revoke->hash_size; i++) {
484  		struct list_head *hash_list;
485  		struct list_head *list_entry;
486  		hash_list = &revoke->hash_table[i];
487  
488  		list_for_each(list_entry, hash_list) {
489  			struct jbd2_revoke_record_s *record;
490  			struct buffer_head *bh;
491  			record = (struct jbd2_revoke_record_s *)list_entry;
492  			bh = __find_get_block(journal->j_fs_dev,
493  					      record->blocknr,
494  					      journal->j_blocksize);
495  			if (bh) {
496  				clear_buffer_revoked(bh);
497  				__brelse(bh);
498  			}
499  		}
500  	}
501  }
502  
503  /* journal_switch_revoke table select j_revoke for next transaction
504   * we do not want to suspend any processing until all revokes are
505   * written -bzzz
506   */
507  void jbd2_journal_switch_revoke_table(journal_t *journal)
508  {
509  	int i;
510  
511  	if (journal->j_revoke == journal->j_revoke_table[0])
512  		journal->j_revoke = journal->j_revoke_table[1];
513  	else
514  		journal->j_revoke = journal->j_revoke_table[0];
515  
516  	for (i = 0; i < journal->j_revoke->hash_size; i++)
517  		INIT_LIST_HEAD(&journal->j_revoke->hash_table[i]);
518  }
519  
520  /*
521   * Write revoke records to the journal for all entries in the current
522   * revoke hash, deleting the entries as we go.
523   */
524  void jbd2_journal_write_revoke_records(transaction_t *transaction,
525  				       struct list_head *log_bufs)
526  {
527  	journal_t *journal = transaction->t_journal;
528  	struct buffer_head *descriptor;
529  	struct jbd2_revoke_record_s *record;
530  	struct jbd2_revoke_table_s *revoke;
531  	struct list_head *hash_list;
532  	int i, offset, count;
533  
534  	descriptor = NULL;
535  	offset = 0;
536  	count = 0;
537  
538  	/* select revoke table for committing transaction */
539  	revoke = journal->j_revoke == journal->j_revoke_table[0] ?
540  		journal->j_revoke_table[1] : journal->j_revoke_table[0];
541  
542  	for (i = 0; i < revoke->hash_size; i++) {
543  		hash_list = &revoke->hash_table[i];
544  
545  		while (!list_empty(hash_list)) {
546  			record = (struct jbd2_revoke_record_s *)
547  				hash_list->next;
548  			write_one_revoke_record(transaction, log_bufs,
549  						&descriptor, &offset, record);
550  			count++;
551  			list_del(&record->hash);
552  			kmem_cache_free(jbd2_revoke_record_cache, record);
553  		}
554  	}
555  	if (descriptor)
556  		flush_descriptor(journal, descriptor, offset);
557  	jbd_debug(1, "Wrote %d revoke records\n", count);
558  }
559  
560  /*
561   * Write out one revoke record.  We need to create a new descriptor
562   * block if the old one is full or if we have not already created one.
563   */
564  
565  static void write_one_revoke_record(transaction_t *transaction,
566  				    struct list_head *log_bufs,
567  				    struct buffer_head **descriptorp,
568  				    int *offsetp,
569  				    struct jbd2_revoke_record_s *record)
570  {
571  	journal_t *journal = transaction->t_journal;
572  	int csum_size = 0;
573  	struct buffer_head *descriptor;
574  	int sz, offset;
575  
576  	/* If we are already aborting, this all becomes a noop.  We
577             still need to go round the loop in
578             jbd2_journal_write_revoke_records in order to free all of the
579             revoke records: only the IO to the journal is omitted. */
580  	if (is_journal_aborted(journal))
581  		return;
582  
583  	descriptor = *descriptorp;
584  	offset = *offsetp;
585  
586  	/* Do we need to leave space at the end for a checksum? */
587  	if (jbd2_journal_has_csum_v2or3(journal))
588  		csum_size = sizeof(struct jbd2_journal_block_tail);
589  
590  	if (jbd2_has_feature_64bit(journal))
591  		sz = 8;
592  	else
593  		sz = 4;
594  
595  	/* Make sure we have a descriptor with space left for the record */
596  	if (descriptor) {
597  		if (offset + sz > journal->j_blocksize - csum_size) {
598  			flush_descriptor(journal, descriptor, offset);
599  			descriptor = NULL;
600  		}
601  	}
602  
603  	if (!descriptor) {
604  		descriptor = jbd2_journal_get_descriptor_buffer(transaction,
605  							JBD2_REVOKE_BLOCK);
606  		if (!descriptor)
607  			return;
608  
609  		/* Record it so that we can wait for IO completion later */
610  		BUFFER_TRACE(descriptor, "file in log_bufs");
611  		jbd2_file_log_bh(log_bufs, descriptor);
612  
613  		offset = sizeof(jbd2_journal_revoke_header_t);
614  		*descriptorp = descriptor;
615  	}
616  
617  	if (jbd2_has_feature_64bit(journal))
618  		* ((__be64 *)(&descriptor->b_data[offset])) =
619  			cpu_to_be64(record->blocknr);
620  	else
621  		* ((__be32 *)(&descriptor->b_data[offset])) =
622  			cpu_to_be32(record->blocknr);
623  	offset += sz;
624  
625  	*offsetp = offset;
626  }
627  
628  /*
629   * Flush a revoke descriptor out to the journal.  If we are aborting,
630   * this is a noop; otherwise we are generating a buffer which needs to
631   * be waited for during commit, so it has to go onto the appropriate
632   * journal buffer list.
633   */
634  
635  static void flush_descriptor(journal_t *journal,
636  			     struct buffer_head *descriptor,
637  			     int offset)
638  {
639  	jbd2_journal_revoke_header_t *header;
640  
641  	if (is_journal_aborted(journal))
642  		return;
643  
644  	header = (jbd2_journal_revoke_header_t *)descriptor->b_data;
645  	header->r_count = cpu_to_be32(offset);
646  	jbd2_descriptor_block_csum_set(journal, descriptor);
647  
648  	set_buffer_jwrite(descriptor);
649  	BUFFER_TRACE(descriptor, "write");
650  	set_buffer_dirty(descriptor);
651  	write_dirty_buffer(descriptor, REQ_SYNC);
652  }
653  #endif
654  
655  /*
656   * Revoke support for recovery.
657   *
658   * Recovery needs to be able to:
659   *
660   *  record all revoke records, including the tid of the latest instance
661   *  of each revoke in the journal
662   *
663   *  check whether a given block in a given transaction should be replayed
664   *  (ie. has not been revoked by a revoke record in that or a subsequent
665   *  transaction)
666   *
667   *  empty the revoke table after recovery.
668   */
669  
670  /*
671   * First, setting revoke records.  We create a new revoke record for
672   * every block ever revoked in the log as we scan it for recovery, and
673   * we update the existing records if we find multiple revokes for a
674   * single block.
675   */
676  
677  int jbd2_journal_set_revoke(journal_t *journal,
678  		       unsigned long long blocknr,
679  		       tid_t sequence)
680  {
681  	struct jbd2_revoke_record_s *record;
682  
683  	record = find_revoke_record(journal, blocknr);
684  	if (record) {
685  		/* If we have multiple occurrences, only record the
686  		 * latest sequence number in the hashed record */
687  		if (tid_gt(sequence, record->sequence))
688  			record->sequence = sequence;
689  		return 0;
690  	}
691  	return insert_revoke_hash(journal, blocknr, sequence);
692  }
693  
694  /*
695   * Test revoke records.  For a given block referenced in the log, has
696   * that block been revoked?  A revoke record with a given transaction
697   * sequence number revokes all blocks in that transaction and earlier
698   * ones, but later transactions still need replayed.
699   */
700  
701  int jbd2_journal_test_revoke(journal_t *journal,
702  			unsigned long long blocknr,
703  			tid_t sequence)
704  {
705  	struct jbd2_revoke_record_s *record;
706  
707  	record = find_revoke_record(journal, blocknr);
708  	if (!record)
709  		return 0;
710  	if (tid_gt(sequence, record->sequence))
711  		return 0;
712  	return 1;
713  }
714  
715  /*
716   * Finally, once recovery is over, we need to clear the revoke table so
717   * that it can be reused by the running filesystem.
718   */
719  
720  void jbd2_journal_clear_revoke(journal_t *journal)
721  {
722  	int i;
723  	struct list_head *hash_list;
724  	struct jbd2_revoke_record_s *record;
725  	struct jbd2_revoke_table_s *revoke;
726  
727  	revoke = journal->j_revoke;
728  
729  	for (i = 0; i < revoke->hash_size; i++) {
730  		hash_list = &revoke->hash_table[i];
731  		while (!list_empty(hash_list)) {
732  			record = (struct jbd2_revoke_record_s*) hash_list->next;
733  			list_del(&record->hash);
734  			kmem_cache_free(jbd2_revoke_record_cache, record);
735  		}
736  	}
737  }
738