/*

   * linux/fs/jbd/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/jbd.h>
  #include <linux/errno.h>
  #include <linux/slab.h>
  #include <linux/list.h>

  #include <linux/init.h>

  #include <linux/bio.h>

  #endif

  #include <linux/log2.h>

  static struct kmem_cache *revoke_record_cache;
  static struct kmem_cache *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 jbd_revoke_record_s

  {
  	struct list_head  hash;
  	tid_t		  sequence;	/* Used for recovery only */

  	unsigned int	  blocknr;

  };
  
  
  /* The revoke table is just a simple hash table of revoke records. */
  struct jbd_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 journal_head **, int *,

  				    struct jbd_revoke_record_s *, int);
  static void flush_descriptor(journal_t *, struct journal_head *, int, int);

  #endif
  
  /* Utility functions to maintain the revoke table */
  
  /* Borrowed from buffer.c: this is a tried and tested block hash function */

  static inline int hash(journal_t *journal, unsigned int block)

  {
  	struct jbd_revoke_table_s *table = journal->j_revoke;
  	int hash_shift = table->hash_shift;
  
  	return ((block << (hash_shift - 6)) ^
  		(block >> 13) ^
  		(block << (hash_shift - 12))) & (table->hash_size - 1);
  }

  static int insert_revoke_hash(journal_t *journal, unsigned int blocknr,

  			      tid_t seq)

  {
  	struct list_head *hash_list;
  	struct jbd_revoke_record_s *record;
  
  repeat:
  	record = kmem_cache_alloc(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
  ", __func__);

  	yield();
  	goto repeat;
  }
  
  /* Find a revoke record in the journal's hash table. */
  
  static struct jbd_revoke_record_s *find_revoke_record(journal_t *journal,

  						      unsigned int blocknr)

  {
  	struct list_head *hash_list;
  	struct jbd_revoke_record_s *record;
  
  	hash_list = &journal->j_revoke->hash_table[hash(journal, blocknr)];
  
  	spin_lock(&journal->j_revoke_lock);
  	record = (struct jbd_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 jbd_revoke_record_s *) record->hash.next;
  	}
  	spin_unlock(&journal->j_revoke_lock);
  	return NULL;
  }

  void journal_destroy_revoke_caches(void)
  {
  	if (revoke_record_cache) {
  		kmem_cache_destroy(revoke_record_cache);
  		revoke_record_cache = NULL;
  	}
  	if (revoke_table_cache) {
  		kmem_cache_destroy(revoke_table_cache);
  		revoke_table_cache = NULL;
  	}
  }

  int __init journal_init_revoke_caches(void)
  {

  	J_ASSERT(!revoke_record_cache);
  	J_ASSERT(!revoke_table_cache);

  	revoke_record_cache = kmem_cache_create("revoke_record",
  					   sizeof(struct jbd_revoke_record_s),

  					   0,
  					   SLAB_HWCACHE_ALIGN|SLAB_TEMPORARY,
  					   NULL);

  	if (!revoke_record_cache)

  		goto record_cache_failure;

  
  	revoke_table_cache = kmem_cache_create("revoke_table",
  					   sizeof(struct jbd_revoke_table_s),

  					   0, SLAB_TEMPORARY, NULL);

  	if (!revoke_table_cache)
  		goto table_cache_failure;

  	return 0;

  table_cache_failure:
  	journal_destroy_revoke_caches();
  record_cache_failure:
  	return -ENOMEM;

  }

  static struct jbd_revoke_table_s *journal_init_revoke_table(int hash_size)

  {

  	int shift = 0;
  	int tmp = hash_size;
  	struct jbd_revoke_table_s *table;

  	table = kmem_cache_alloc(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(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 journal_destroy_revoke_table(struct jbd_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(revoke_table_cache, table);
  }

  /* Initialise the revoke table for a given journal to a given size. */
  int 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] = journal_init_revoke_table(hash_size);
  	if (!journal->j_revoke_table[0])
  		goto fail0;

  	journal->j_revoke_table[1] = 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:
  	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 journal_destroy_revoke(journal_t *journal)
  {

  	journal->j_revoke = NULL;

  	if (journal->j_revoke_table[0])
  		journal_destroy_revoke_table(journal->j_revoke_table[0]);
  	if (journal->j_revoke_table[1])
  		journal_destroy_revoke_table(journal->j_revoke_table[1]);

  }
  
  
  #ifdef __KERNEL__

  /*

   * 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 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, journal_revoke() will decrement its b_count
   * by one.
   */

  int journal_revoke(handle_t *handle, unsigned int 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 (!journal_set_features(journal, 0, 0, JFS_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 JBD_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 journal_forget");
  			journal_forget(handle, bh_in);
  		} else {
  			BUFFER_TRACE(bh, "call brelse");
  			__brelse(bh);
  		}
  	}

  	jbd_debug(2, "insert revoke for block %u, bh_in=%p
  ", 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 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 journal_cancel_revoke(handle_t *handle, struct journal_head *jh)
  {
  	struct jbd_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
  ", 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
  ", (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(revoke_record_cache, record);
  			did_revoke = 1;
  		}
  	}
  
  #ifdef JBD_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_flags clears revoked flag of buffers in
   * revoke table to reflect there is no revoked buffer in the next
   * transaction which is going to be started.
   */
  void journal_clear_buffer_revoked_flags(journal_t *journal)
  {
  	struct jbd_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 jbd_revoke_record_s *record;
  			struct buffer_head *bh;
  			record = (struct jbd_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 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 journal_write_revoke_records(journal_t *journal,

  				  transaction_t *transaction, int write_op)

  {
  	struct journal_head *descriptor;
  	struct jbd_revoke_record_s *record;
  	struct jbd_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 jbd_revoke_record_s *)

  				hash_list->next;
  			write_one_revoke_record(journal, transaction,

  						&descriptor, &offset,

  						record, write_op);

  			count++;
  			list_del(&record->hash);
  			kmem_cache_free(revoke_record_cache, record);
  		}
  	}
  	if (descriptor)

  		flush_descriptor(journal, descriptor, offset, write_op);

  	jbd_debug(1, "Wrote %d revoke records
  ", 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 journal_head **descriptorp,

  				    int *offsetp,

  				    struct jbd_revoke_record_s *record,
  				    int write_op)

  {
  	struct journal_head *descriptor;
  	int offset;
  	journal_header_t *header;
  
  	/* If we are already aborting, this all becomes a noop.  We
             still need to go round the loop in
             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;
  
  	/* Make sure we have a descriptor with space left for the record */
  	if (descriptor) {
  		if (offset == journal->j_blocksize) {

  			flush_descriptor(journal, descriptor, offset, write_op);

  			descriptor = NULL;
  		}
  	}
  
  	if (!descriptor) {
  		descriptor = journal_get_descriptor_buffer(journal);
  		if (!descriptor)
  			return;
  		header = (journal_header_t *) &jh2bh(descriptor)->b_data[0];
  		header->h_magic     = cpu_to_be32(JFS_MAGIC_NUMBER);
  		header->h_blocktype = cpu_to_be32(JFS_REVOKE_BLOCK);
  		header->h_sequence  = cpu_to_be32(transaction->t_tid);
  
  		/* Record it so that we can wait for IO completion later */
  		JBUFFER_TRACE(descriptor, "file as BJ_LogCtl");
  		journal_file_buffer(descriptor, transaction, BJ_LogCtl);
  
  		offset = sizeof(journal_revoke_header_t);
  		*descriptorp = descriptor;
  	}

  	* ((__be32 *)(&jh2bh(descriptor)->b_data[offset])) =

  		cpu_to_be32(record->blocknr);
  	offset += 4;
  	*offsetp = offset;
  }

  /*

   * 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 journal_head *descriptor,

  			     int offset, int write_op)

  {
  	journal_revoke_header_t *header;
  	struct buffer_head *bh = jh2bh(descriptor);
  
  	if (is_journal_aborted(journal)) {
  		put_bh(bh);
  		return;
  	}
  
  	header = (journal_revoke_header_t *) jh2bh(descriptor)->b_data;
  	header->r_count = cpu_to_be32(offset);
  	set_buffer_jwrite(bh);
  	BUFFER_TRACE(bh, "write");
  	set_buffer_dirty(bh);

  	write_dirty_buffer(bh, 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 journal_set_revoke(journal_t *journal,

  		       unsigned int blocknr,

  		       tid_t sequence)
  {
  	struct jbd_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 journal_test_revoke(journal_t *journal,

  			unsigned int blocknr,

  			tid_t sequence)
  {
  	struct jbd_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 journal_clear_revoke(journal_t *journal)
  {
  	int i;
  	struct list_head *hash_list;
  	struct jbd_revoke_record_s *record;
  	struct jbd_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 jbd_revoke_record_s*) hash_list->next;
  			list_del(&record->hash);
  			kmem_cache_free(revoke_record_cache, record);
  		}
  	}
  }