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32 results

ring_buffer.c

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  • revoke.c 22.26 KiB
    /*
     * linux/fs/jbd2/revoke.c
     *
     * Written by Stephen C. Tweedie <sct@redhat.com>, 2000
     *
     * Copyright 2000 Red Hat corp --- All Rights Reserved
     *
     * This file is part of the Linux kernel and is made available under
     * the terms of the GNU General Public License, version 2, or at your
     * option, any later version, incorporated herein by reference.
     *
     * Journal revoke routines for the generic filesystem journaling code;
     * part of the ext2fs journaling system.
     *
     * Revoke is the mechanism used to prevent old log records for deleted
     * metadata from being replayed on top of newer data using the same
     * blocks.  The revoke mechanism is used in two separate places:
     *
     * + Commit: during commit we write the entire list of the current
     *   transaction's revoked blocks to the journal
     *
     * + Recovery: during recovery we record the transaction ID of all
     *   revoked blocks.  If there are multiple revoke records in the log
     *   for a single block, only the last one counts, and if there is a log
     *   entry for a block beyond the last revoke, then that log entry still
     *   gets replayed.
     *
     * We can get interactions between revokes and new log data within a
     * single transaction:
     *
     * Block is revoked and then journaled:
     *   The desired end result is the journaling of the new block, so we
     *   cancel the revoke before the transaction commits.
     *
     * Block is journaled and then revoked:
     *   The revoke must take precedence over the write of the block, so we
     *   need either to cancel the journal entry or to write the revoke
     *   later in the log than the log block.  In this case, we choose the
     *   latter: journaling a block cancels any revoke record for that block
     *   in the current transaction, so any revoke for that block in the
     *   transaction must have happened after the block was journaled and so
     *   the revoke must take precedence.
     *
     * Block is revoked and then written as data:
     *   The data write is allowed to succeed, but the revoke is _not_
     *   cancelled.  We still need to prevent old log records from
     *   overwriting the new data.  We don't even need to clear the revoke
     *   bit here.
     *
     * We cache revoke status of a buffer in the current transaction in b_states
     * bits.  As the name says, revokevalid flag indicates that the cached revoke
     * status of a buffer is valid and we can rely on the cached status.
     *
     * Revoke information on buffers is a tri-state value:
     *
     * RevokeValid clear:	no cached revoke status, need to look it up
     * RevokeValid set, Revoked clear:
     *			buffer has not been revoked, and cancel_revoke
     *			need do nothing.
     * RevokeValid set, Revoked set:
     *			buffer has been revoked.
     *
     * Locking rules:
     * We keep two hash tables of revoke records. One hashtable belongs to the
     * running transaction (is pointed to by journal->j_revoke), the other one
     * belongs to the committing transaction. Accesses to the second hash table
     * happen only from the kjournald and no other thread touches this table.  Also
     * journal_switch_revoke_table() which switches which hashtable belongs to the
     * running and which to the committing transaction is called only from
     * kjournald. Therefore we need no locks when accessing the hashtable belonging
     * to the committing transaction.
     *
     * All users operating on the hash table belonging to the running transaction
     * have a handle to the transaction. Therefore they are safe from kjournald
     * switching hash tables under them. For operations on the lists of entries in
     * the hash table j_revoke_lock is used.
     *
     * Finally, also replay code uses the hash tables but at this moment no one else
     * can touch them (filesystem isn't mounted yet) and hence no locking is
     * needed.
     */
    
    #ifndef __KERNEL__
    #include "jfs_user.h"
    #else
    #include <linux/time.h>
    #include <linux/fs.h>
    #include <linux/jbd2.h>
    #include <linux/errno.h>
    #include <linux/slab.h>
    #include <linux/list.h>
    #include <linux/init.h>
    #include <linux/bio.h>
    #include <linux/log2.h>
    #include <linux/hash.h>
    #endif
    
    static struct kmem_cache *jbd2_revoke_record_cache;
    static struct kmem_cache *jbd2_revoke_table_cache;
    
    /* Each revoke record represents one single revoked block.  During
       journal replay, this involves recording the transaction ID of the
       last transaction to revoke this block. */
    
    struct jbd2_revoke_record_s
    {
    	struct list_head  hash;
    	tid_t		  sequence;	/* Used for recovery only */
    	unsigned long long	  blocknr;
    };
    
    
    /* The revoke table is just a simple hash table of revoke records. */
    struct jbd2_revoke_table_s
    {
    	/* It is conceivable that we might want a larger hash table
    	 * for recovery.  Must be a power of two. */
    	int		  hash_size;
    	int		  hash_shift;
    	struct list_head *hash_table;
    };
    
    
    #ifdef __KERNEL__
    static void write_one_revoke_record(journal_t *, transaction_t *,
    				    struct list_head *,
    				    struct buffer_head **, int *,
    				    struct jbd2_revoke_record_s *, int);
    static void flush_descriptor(journal_t *, struct buffer_head *, int, int);
    #endif
    
    /* Utility functions to maintain the revoke table */
    
    static inline int hash(journal_t *journal, unsigned long long block)
    {
    	return hash_64(block, journal->j_revoke->hash_shift);
    }
    
    static int insert_revoke_hash(journal_t *journal, unsigned long long blocknr,
    			      tid_t seq)
    {
    	struct list_head *hash_list;
    	struct jbd2_revoke_record_s *record;
    
    repeat:
    	record = kmem_cache_alloc(jbd2_revoke_record_cache, GFP_NOFS);
    	if (!record)
    		goto oom;
    
    	record->sequence = seq;
    	record->blocknr = blocknr;
    	hash_list = &journal->j_revoke->hash_table[hash(journal, blocknr)];
    	spin_lock(&journal->j_revoke_lock);
    	list_add(&record->hash, hash_list);
    	spin_unlock(&journal->j_revoke_lock);
    	return 0;
    
    oom:
    	if (!journal_oom_retry)
    		return -ENOMEM;
    	jbd_debug(1, "ENOMEM in %s, retrying\n", __func__);
    	yield();
    	goto repeat;
    }
    
    /* Find a revoke record in the journal's hash table. */
    
    static struct jbd2_revoke_record_s *find_revoke_record(journal_t *journal,
    						      unsigned long long blocknr)
    {
    	struct list_head *hash_list;
    	struct jbd2_revoke_record_s *record;
    
    	hash_list = &journal->j_revoke->hash_table[hash(journal, blocknr)];
    
    	spin_lock(&journal->j_revoke_lock);
    	record = (struct jbd2_revoke_record_s *) hash_list->next;
    	while (&(record->hash) != hash_list) {
    		if (record->blocknr == blocknr) {
    			spin_unlock(&journal->j_revoke_lock);
    			return record;
    		}
    		record = (struct jbd2_revoke_record_s *) record->hash.next;
    	}
    	spin_unlock(&journal->j_revoke_lock);
    	return NULL;
    }
    
    void jbd2_journal_destroy_revoke_caches(void)
    {
    	if (jbd2_revoke_record_cache) {
    		kmem_cache_destroy(jbd2_revoke_record_cache);
    		jbd2_revoke_record_cache = NULL;
    	}
    	if (jbd2_revoke_table_cache) {
    		kmem_cache_destroy(jbd2_revoke_table_cache);
    		jbd2_revoke_table_cache = NULL;
    	}
    }
    
    int __init jbd2_journal_init_revoke_caches(void)
    {
    	J_ASSERT(!jbd2_revoke_record_cache);
    	J_ASSERT(!jbd2_revoke_table_cache);
    
    	jbd2_revoke_record_cache = KMEM_CACHE(jbd2_revoke_record_s,
    					SLAB_HWCACHE_ALIGN|SLAB_TEMPORARY);
    	if (!jbd2_revoke_record_cache)
    		goto record_cache_failure;
    
    	jbd2_revoke_table_cache = KMEM_CACHE(jbd2_revoke_table_s,
    					     SLAB_TEMPORARY);
    	if (!jbd2_revoke_table_cache)
    		goto table_cache_failure;
    	return 0;
    table_cache_failure:
    	jbd2_journal_destroy_revoke_caches();
    record_cache_failure:
    		return -ENOMEM;
    }
    
    static struct jbd2_revoke_table_s *jbd2_journal_init_revoke_table(int hash_size)
    {
    	int shift = 0;
    	int tmp = hash_size;
    	struct jbd2_revoke_table_s *table;
    
    	table = kmem_cache_alloc(jbd2_revoke_table_cache, GFP_KERNEL);
    	if (!table)
    		goto out;
    
    	while((tmp >>= 1UL) != 0UL)
    		shift++;
    
    	table->hash_size = hash_size;
    	table->hash_shift = shift;
    	table->hash_table =
    		kmalloc(hash_size * sizeof(struct list_head), GFP_KERNEL);
    	if (!table->hash_table) {
    		kmem_cache_free(jbd2_revoke_table_cache, table);
    		table = NULL;
    		goto out;
    	}
    
    	for (tmp = 0; tmp < hash_size; tmp++)
    		INIT_LIST_HEAD(&table->hash_table[tmp]);
    
    out:
    	return table;
    }
    
    static void jbd2_journal_destroy_revoke_table(struct jbd2_revoke_table_s *table)
    {
    	int i;
    	struct list_head *hash_list;
    
    	for (i = 0; i < table->hash_size; i++) {
    		hash_list = &table->hash_table[i];
    		J_ASSERT(list_empty(hash_list));
    	}
    
    	kfree(table->hash_table);
    	kmem_cache_free(jbd2_revoke_table_cache, table);
    }
    
    /* Initialise the revoke table for a given journal to a given size. */
    int jbd2_journal_init_revoke(journal_t *journal, int hash_size)
    {
    	J_ASSERT(journal->j_revoke_table[0] == NULL);
    	J_ASSERT(is_power_of_2(hash_size));
    
    	journal->j_revoke_table[0] = jbd2_journal_init_revoke_table(hash_size);
    	if (!journal->j_revoke_table[0])
    		goto fail0;
    
    	journal->j_revoke_table[1] = jbd2_journal_init_revoke_table(hash_size);
    	if (!journal->j_revoke_table[1])
    		goto fail1;
    
    	journal->j_revoke = journal->j_revoke_table[1];
    
    	spin_lock_init(&journal->j_revoke_lock);
    
    	return 0;
    
    fail1:
    	jbd2_journal_destroy_revoke_table(journal->j_revoke_table[0]);
    fail0:
    	return -ENOMEM;
    }
    
    /* Destroy a journal's revoke table.  The table must already be empty! */
    void jbd2_journal_destroy_revoke(journal_t *journal)
    {
    	journal->j_revoke = NULL;
    	if (journal->j_revoke_table[0])
    		jbd2_journal_destroy_revoke_table(journal->j_revoke_table[0]);
    	if (journal->j_revoke_table[1])
    		jbd2_journal_destroy_revoke_table(journal->j_revoke_table[1]);
    }
    
    
    #ifdef __KERNEL__
    
    /*
     * jbd2_journal_revoke: revoke a given buffer_head from the journal.  This
     * prevents the block from being replayed during recovery if we take a
     * crash after this current transaction commits.  Any subsequent
     * metadata writes of the buffer in this transaction cancel the
     * revoke.
     *
     * Note that this call may block --- it is up to the caller to make
     * sure that there are no further calls to journal_write_metadata
     * before the revoke is complete.  In ext3, this implies calling the
     * revoke before clearing the block bitmap when we are deleting
     * metadata.
     *
     * Revoke performs a jbd2_journal_forget on any buffer_head passed in as a
     * parameter, but does _not_ forget the buffer_head if the bh was only
     * found implicitly.
     *
     * bh_in may not be a journalled buffer - it may have come off
     * the hash tables without an attached journal_head.
     *
     * If bh_in is non-zero, jbd2_journal_revoke() will decrement its b_count
     * by one.
     */
    
    int jbd2_journal_revoke(handle_t *handle, unsigned long long blocknr,
    		   struct buffer_head *bh_in)
    {
    	struct buffer_head *bh = NULL;
    	journal_t *journal;
    	struct block_device *bdev;
    	int err;
    
    	might_sleep();
    	if (bh_in)
    		BUFFER_TRACE(bh_in, "enter");
    
    	journal = handle->h_transaction->t_journal;
    	if (!jbd2_journal_set_features(journal, 0, 0, JBD2_FEATURE_INCOMPAT_REVOKE)){
    		J_ASSERT (!"Cannot set revoke feature!");
    		return -EINVAL;
    	}
    
    	bdev = journal->j_fs_dev;
    	bh = bh_in;
    
    	if (!bh) {
    		bh = __find_get_block(bdev, blocknr, journal->j_blocksize);
    		if (bh)
    			BUFFER_TRACE(bh, "found on hash");
    	}
    #ifdef JBD2_EXPENSIVE_CHECKING
    	else {
    		struct buffer_head *bh2;
    
    		/* If there is a different buffer_head lying around in
    		 * memory anywhere... */
    		bh2 = __find_get_block(bdev, blocknr, journal->j_blocksize);
    		if (bh2) {
    			/* ... and it has RevokeValid status... */
    			if (bh2 != bh && buffer_revokevalid(bh2))
    				/* ...then it better be revoked too,
    				 * since it's illegal to create a revoke
    				 * record against a buffer_head which is
    				 * not marked revoked --- that would
    				 * risk missing a subsequent revoke
    				 * cancel. */
    				J_ASSERT_BH(bh2, buffer_revoked(bh2));
    			put_bh(bh2);
    		}
    	}
    #endif
    
    	/* We really ought not ever to revoke twice in a row without
               first having the revoke cancelled: it's illegal to free a
               block twice without allocating it in between! */
    	if (bh) {
    		if (!J_EXPECT_BH(bh, !buffer_revoked(bh),
    				 "inconsistent data on disk")) {
    			if (!bh_in)
    				brelse(bh);
    			return -EIO;
    		}
    		set_buffer_revoked(bh);
    		set_buffer_revokevalid(bh);
    		if (bh_in) {
    			BUFFER_TRACE(bh_in, "call jbd2_journal_forget");
    			jbd2_journal_forget(handle, bh_in);
    		} else {
    			BUFFER_TRACE(bh, "call brelse");
    			__brelse(bh);
    		}
    	}
    
    	jbd_debug(2, "insert revoke for block %llu, bh_in=%p\n",blocknr, bh_in);
    	err = insert_revoke_hash(journal, blocknr,
    				handle->h_transaction->t_tid);
    	BUFFER_TRACE(bh_in, "exit");
    	return err;
    }
    
    /*
     * Cancel an outstanding revoke.  For use only internally by the
     * journaling code (called from jbd2_journal_get_write_access).
     *
     * We trust buffer_revoked() on the buffer if the buffer is already
     * being journaled: if there is no revoke pending on the buffer, then we
     * don't do anything here.
     *
     * This would break if it were possible for a buffer to be revoked and
     * discarded, and then reallocated within the same transaction.  In such
     * a case we would have lost the revoked bit, but when we arrived here
     * the second time we would still have a pending revoke to cancel.  So,
     * do not trust the Revoked bit on buffers unless RevokeValid is also
     * set.
     */
    int jbd2_journal_cancel_revoke(handle_t *handle, struct journal_head *jh)
    {
    	struct jbd2_revoke_record_s *record;
    	journal_t *journal = handle->h_transaction->t_journal;
    	int need_cancel;
    	int did_revoke = 0;	/* akpm: debug */
    	struct buffer_head *bh = jh2bh(jh);
    
    	jbd_debug(4, "journal_head %p, cancelling revoke\n", jh);
    
    	/* Is the existing Revoke bit valid?  If so, we trust it, and
    	 * only perform the full cancel if the revoke bit is set.  If
    	 * not, we can't trust the revoke bit, and we need to do the
    	 * full search for a revoke record. */
    	if (test_set_buffer_revokevalid(bh)) {
    		need_cancel = test_clear_buffer_revoked(bh);
    	} else {
    		need_cancel = 1;
    		clear_buffer_revoked(bh);
    	}
    
    	if (need_cancel) {
    		record = find_revoke_record(journal, bh->b_blocknr);
    		if (record) {
    			jbd_debug(4, "cancelled existing revoke on "
    				  "blocknr %llu\n", (unsigned long long)bh->b_blocknr);
    			spin_lock(&journal->j_revoke_lock);
    			list_del(&record->hash);
    			spin_unlock(&journal->j_revoke_lock);
    			kmem_cache_free(jbd2_revoke_record_cache, record);
    			did_revoke = 1;
    		}
    	}
    
    #ifdef JBD2_EXPENSIVE_CHECKING
    	/* There better not be one left behind by now! */
    	record = find_revoke_record(journal, bh->b_blocknr);
    	J_ASSERT_JH(jh, record == NULL);
    #endif
    
    	/* Finally, have we just cleared revoke on an unhashed
    	 * buffer_head?  If so, we'd better make sure we clear the
    	 * revoked status on any hashed alias too, otherwise the revoke
    	 * state machine will get very upset later on. */
    	if (need_cancel) {
    		struct buffer_head *bh2;
    		bh2 = __find_get_block(bh->b_bdev, bh->b_blocknr, bh->b_size);
    		if (bh2) {
    			if (bh2 != bh)
    				clear_buffer_revoked(bh2);
    			__brelse(bh2);
    		}
    	}
    	return did_revoke;
    }
    
    /*
     * journal_clear_revoked_flag clears revoked flag of buffers in
     * revoke table to reflect there is no revoked buffers in the next
     * transaction which is going to be started.
     */
    void jbd2_clear_buffer_revoked_flags(journal_t *journal)
    {
    	struct jbd2_revoke_table_s *revoke = journal->j_revoke;
    	int i = 0;
    
    	for (i = 0; i < revoke->hash_size; i++) {
    		struct list_head *hash_list;
    		struct list_head *list_entry;
    		hash_list = &revoke->hash_table[i];
    
    		list_for_each(list_entry, hash_list) {
    			struct jbd2_revoke_record_s *record;
    			struct buffer_head *bh;
    			record = (struct jbd2_revoke_record_s *)list_entry;
    			bh = __find_get_block(journal->j_fs_dev,
    					      record->blocknr,
    					      journal->j_blocksize);
    			if (bh) {
    				clear_buffer_revoked(bh);
    				__brelse(bh);
    			}
    		}
    	}
    }
    
    /* journal_switch_revoke table select j_revoke for next transaction
     * we do not want to suspend any processing until all revokes are
     * written -bzzz
     */
    void jbd2_journal_switch_revoke_table(journal_t *journal)
    {
    	int i;
    
    	if (journal->j_revoke == journal->j_revoke_table[0])
    		journal->j_revoke = journal->j_revoke_table[1];
    	else
    		journal->j_revoke = journal->j_revoke_table[0];
    
    	for (i = 0; i < journal->j_revoke->hash_size; i++)
    		INIT_LIST_HEAD(&journal->j_revoke->hash_table[i]);
    }
    
    /*
     * Write revoke records to the journal for all entries in the current
     * revoke hash, deleting the entries as we go.
     */
    void jbd2_journal_write_revoke_records(journal_t *journal,
    				       transaction_t *transaction,
    				       struct list_head *log_bufs,
    				       int write_op)
    {
    	struct buffer_head *descriptor;
    	struct jbd2_revoke_record_s *record;
    	struct jbd2_revoke_table_s *revoke;
    	struct list_head *hash_list;
    	int i, offset, count;
    
    	descriptor = NULL;
    	offset = 0;
    	count = 0;
    
    	/* select revoke table for committing transaction */
    	revoke = journal->j_revoke == journal->j_revoke_table[0] ?
    		journal->j_revoke_table[1] : journal->j_revoke_table[0];
    
    	for (i = 0; i < revoke->hash_size; i++) {
    		hash_list = &revoke->hash_table[i];
    
    		while (!list_empty(hash_list)) {
    			record = (struct jbd2_revoke_record_s *)
    				hash_list->next;
    			write_one_revoke_record(journal, transaction, log_bufs,
    						&descriptor, &offset,
    						record, write_op);
    			count++;
    			list_del(&record->hash);
    			kmem_cache_free(jbd2_revoke_record_cache, record);
    		}
    	}
    	if (descriptor)
    		flush_descriptor(journal, descriptor, offset, write_op);
    	jbd_debug(1, "Wrote %d revoke records\n", count);
    }
    
    /*
     * Write out one revoke record.  We need to create a new descriptor
     * block if the old one is full or if we have not already created one.
     */
    
    static void write_one_revoke_record(journal_t *journal,
    				    transaction_t *transaction,
    				    struct list_head *log_bufs,
    				    struct buffer_head **descriptorp,
    				    int *offsetp,
    				    struct jbd2_revoke_record_s *record,
    				    int write_op)
    {
    	int csum_size = 0;
    	struct buffer_head *descriptor;
    	int sz, offset;
    	journal_header_t *header;
    
    	/* If we are already aborting, this all becomes a noop.  We
               still need to go round the loop in
               jbd2_journal_write_revoke_records in order to free all of the
               revoke records: only the IO to the journal is omitted. */
    	if (is_journal_aborted(journal))
    		return;
    
    	descriptor = *descriptorp;
    	offset = *offsetp;
    
    	/* Do we need to leave space at the end for a checksum? */
    	if (jbd2_journal_has_csum_v2or3(journal))
    		csum_size = sizeof(struct jbd2_journal_revoke_tail);
    
    	if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_64BIT))
    		sz = 8;
    	else
    		sz = 4;
    
    	/* Make sure we have a descriptor with space left for the record */
    	if (descriptor) {
    		if (offset + sz > journal->j_blocksize - csum_size) {
    			flush_descriptor(journal, descriptor, offset, write_op);
    			descriptor = NULL;
    		}
    	}
    
    	if (!descriptor) {
    		descriptor = jbd2_journal_get_descriptor_buffer(journal);
    		if (!descriptor)
    			return;
    		header = (journal_header_t *)descriptor->b_data;
    		header->h_magic     = cpu_to_be32(JBD2_MAGIC_NUMBER);
    		header->h_blocktype = cpu_to_be32(JBD2_REVOKE_BLOCK);
    		header->h_sequence  = cpu_to_be32(transaction->t_tid);
    
    		/* Record it so that we can wait for IO completion later */
    		BUFFER_TRACE(descriptor, "file in log_bufs");
    		jbd2_file_log_bh(log_bufs, descriptor);
    
    		offset = sizeof(jbd2_journal_revoke_header_t);
    		*descriptorp = descriptor;
    	}
    
    	if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_64BIT))
    		* ((__be64 *)(&descriptor->b_data[offset])) =
    			cpu_to_be64(record->blocknr);
    	else
    		* ((__be32 *)(&descriptor->b_data[offset])) =
    			cpu_to_be32(record->blocknr);
    	offset += sz;
    
    	*offsetp = offset;
    }
    
    static void jbd2_revoke_csum_set(journal_t *j, struct buffer_head *bh)
    {
    	struct jbd2_journal_revoke_tail *tail;
    	__u32 csum;
    
    	if (!jbd2_journal_has_csum_v2or3(j))
    		return;
    
    	tail = (struct jbd2_journal_revoke_tail *)(bh->b_data + j->j_blocksize -
    			sizeof(struct jbd2_journal_revoke_tail));
    	tail->r_checksum = 0;
    	csum = jbd2_chksum(j, j->j_csum_seed, bh->b_data, j->j_blocksize);
    	tail->r_checksum = cpu_to_be32(csum);
    }
    
    /*
     * Flush a revoke descriptor out to the journal.  If we are aborting,
     * this is a noop; otherwise we are generating a buffer which needs to
     * be waited for during commit, so it has to go onto the appropriate
     * journal buffer list.
     */
    
    static void flush_descriptor(journal_t *journal,
    			     struct buffer_head *descriptor,
    			     int offset, int write_op)
    {
    	jbd2_journal_revoke_header_t *header;
    
    	if (is_journal_aborted(journal)) {
    		put_bh(descriptor);
    		return;
    	}
    
    	header = (jbd2_journal_revoke_header_t *)descriptor->b_data;
    	header->r_count = cpu_to_be32(offset);
    	jbd2_revoke_csum_set(journal, descriptor);
    
    	set_buffer_jwrite(descriptor);
    	BUFFER_TRACE(descriptor, "write");
    	set_buffer_dirty(descriptor);
    	write_dirty_buffer(descriptor, write_op);
    }
    #endif
    
    /*
     * Revoke support for recovery.
     *
     * Recovery needs to be able to:
     *
     *  record all revoke records, including the tid of the latest instance
     *  of each revoke in the journal
     *
     *  check whether a given block in a given transaction should be replayed
     *  (ie. has not been revoked by a revoke record in that or a subsequent
     *  transaction)
     *
     *  empty the revoke table after recovery.
     */
    
    /*
     * First, setting revoke records.  We create a new revoke record for
     * every block ever revoked in the log as we scan it for recovery, and
     * we update the existing records if we find multiple revokes for a
     * single block.
     */
    
    int jbd2_journal_set_revoke(journal_t *journal,
    		       unsigned long long blocknr,
    		       tid_t sequence)
    {
    	struct jbd2_revoke_record_s *record;
    
    	record = find_revoke_record(journal, blocknr);
    	if (record) {
    		/* If we have multiple occurrences, only record the
    		 * latest sequence number in the hashed record */
    		if (tid_gt(sequence, record->sequence))
    			record->sequence = sequence;
    		return 0;
    	}
    	return insert_revoke_hash(journal, blocknr, sequence);
    }
    
    /*
     * Test revoke records.  For a given block referenced in the log, has
     * that block been revoked?  A revoke record with a given transaction
     * sequence number revokes all blocks in that transaction and earlier
     * ones, but later transactions still need replayed.
     */
    
    int jbd2_journal_test_revoke(journal_t *journal,
    			unsigned long long blocknr,
    			tid_t sequence)
    {
    	struct jbd2_revoke_record_s *record;
    
    	record = find_revoke_record(journal, blocknr);
    	if (!record)
    		return 0;
    	if (tid_gt(sequence, record->sequence))
    		return 0;
    	return 1;
    }
    
    /*
     * Finally, once recovery is over, we need to clear the revoke table so
     * that it can be reused by the running filesystem.
     */
    
    void jbd2_journal_clear_revoke(journal_t *journal)
    {
    	int i;
    	struct list_head *hash_list;
    	struct jbd2_revoke_record_s *record;
    	struct jbd2_revoke_table_s *revoke;
    
    	revoke = journal->j_revoke;
    
    	for (i = 0; i < revoke->hash_size; i++) {
    		hash_list = &revoke->hash_table[i];
    		while (!list_empty(hash_list)) {
    			record = (struct jbd2_revoke_record_s*) hash_list->next;
    			list_del(&record->hash);
    			kmem_cache_free(jbd2_revoke_record_cache, record);
    		}
    	}
    }