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revoke.c

/*
 * linux/fs/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.
 *
 * 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 *                buffer has not been revoked, and cancel_revoke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.  
 */

#ifndef __KERNEL__
#include "jfs_user.h"
#else
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/jbd.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/locks.h>
#include <linux/list.h>
#include <linux/smp_lock.h>
#include <linux/init.h>
#endif

static kmem_cache_t *revoke_record_cache;
static kmem_cache_t *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 long       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 *);
static void flush_descriptor(journal_t *, struct journal_head *, 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 long 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 long blocknr,
                        tid_t seq)
{
      struct list_head *hash_list;
      struct jbd_revoke_record_s *record;

#ifdef __KERNEL__
repeat:
#endif
      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)];
      list_add(&record->hash, hash_list);
      return 0;

oom:
#ifdef __KERNEL__
      if (!journal_oom_retry)
            return -ENOMEM;
      jbd_debug(1, "ENOMEM in " __FUNCTION__ ", retrying.\n");
      current->policy |= SCHED_YIELD;
      schedule();
      goto repeat;
#else
      return -ENOMEM;
#endif
}

/* Find a revoke record in the journal's hash table. */

static struct jbd_revoke_record_s *find_revoke_record(journal_t *journal,
                                          unsigned long blocknr)
{
      struct list_head *hash_list;
      struct jbd_revoke_record_s *record;
      
      hash_list = &journal->j_revoke->hash_table[hash(journal, blocknr)];

      record = (struct jbd_revoke_record_s *) hash_list->next;
      while (&(record->hash) != hash_list) {
            if (record->blocknr == blocknr)
                  return record;
            record = (struct jbd_revoke_record_s *) record->hash.next;
      }
      return NULL;
}

int __init journal_init_revoke_caches(void)
{
      revoke_record_cache = kmem_cache_create("revoke_record",
                                 sizeof(struct jbd_revoke_record_s),
                                 0, SLAB_HWCACHE_ALIGN, NULL, NULL);
      if (revoke_record_cache == 0)
            return -ENOMEM;

      revoke_table_cache = kmem_cache_create("revoke_table",
                                 sizeof(struct jbd_revoke_table_s),
                                 0, 0, NULL, NULL);
      if (revoke_table_cache == 0) {
            kmem_cache_destroy(revoke_record_cache);
            revoke_record_cache = NULL;
            return -ENOMEM;
      }
      return 0;
}     

void journal_destroy_revoke_caches(void)
{
      kmem_cache_destroy(revoke_record_cache);
      revoke_record_cache = 0;
      kmem_cache_destroy(revoke_table_cache);
      revoke_table_cache = 0;
}

/* Initialise the revoke table for a given journal to a given size. */

int journal_init_revoke(journal_t *journal, int hash_size)
{
      int shift, tmp;
      
      J_ASSERT (journal->j_revoke == NULL);
      
      journal->j_revoke = kmem_cache_alloc(revoke_table_cache, GFP_KERNEL);
      if (!journal->j_revoke)
            return -ENOMEM;
      
      /* Check that the hash_size is a power of two */
      J_ASSERT ((hash_size & (hash_size-1)) == 0);

      journal->j_revoke->hash_size = hash_size;

      shift = 0;
      tmp = hash_size;
      while((tmp >>= 1UL) != 0UL)
            shift++;
      journal->j_revoke->hash_shift = shift;

      journal->j_revoke->hash_table =
            kmalloc(hash_size * sizeof(struct list_head), GFP_KERNEL);
      if (!journal->j_revoke->hash_table) {
            kmem_cache_free(revoke_table_cache, journal->j_revoke);
            journal->j_revoke = NULL;
            return -ENOMEM;
      }
      
      for (tmp = 0; tmp < hash_size; tmp++)
            INIT_LIST_HEAD(&journal->j_revoke->hash_table[tmp]);
      
      return 0;
}

/* Destoy a journal's revoke table.  The table must already be empty! */

void journal_destroy_revoke(journal_t *journal)
{
      struct jbd_revoke_table_s *table;
      struct list_head *hash_list;
      int i;
      
      table = journal->j_revoke;
      if (!table)
            return;
      
      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);
      journal->j_revoke = NULL;
}


#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 long blocknr, 
               struct buffer_head *bh_in)
{
      struct buffer_head *bh = NULL;
      journal_t *journal;
      kdev_t dev;
      int err;

      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;
      }

      dev = journal->j_fs_dev;
      bh = bh_in;

      if (!bh) {
            bh = get_hash_table(dev, 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 = get_hash_table(dev, blocknr, journal->j_blocksize);
            if (bh2) {
                  /* ... and it has RevokeValid status... */
                  if ((bh2 != bh) &&
                      test_bit(BH_RevokeValid, &bh2->b_state))
                        /* ...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, test_bit(BH_Revoked, &
                                            bh2->b_state));
                  __brelse(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) {
            J_ASSERT_BH(bh, !test_bit(BH_Revoked, &bh->b_state));
            set_bit(BH_Revoked, &bh->b_state);
            set_bit(BH_RevokeValid, &bh->b_state);
            if (bh_in) {
                  BUFFER_TRACE(bh_in, "call journal_forget");
                  journal_forget(handle, bh_in);
            } else {
                  BUFFER_TRACE(bh, "call brelse");
                  __brelse(bh);
            }
      }

      lock_journal(journal);
      jbd_debug(2, "insert revoke for block %lu, bh_in=%p\n", blocknr, bh_in);
      err = insert_revoke_hash(journal, blocknr,
                        handle->h_transaction->t_tid);
      unlock_journal(journal);
      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 the BH_Revoked bit 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.
 *
 * The caller must have the journal locked.
 */
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\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_and_set_bit(BH_RevokeValid, &bh->b_state))
            need_cancel = (test_and_clear_bit(BH_Revoked, &bh->b_state));
      else {
            need_cancel = 1;
            clear_bit(BH_Revoked, &bh->b_state);
      }

      if (need_cancel) {
            record = find_revoke_record(journal, bh->b_blocknr);
            if (record) {
                  jbd_debug(4, "cancelled existing revoke on "
                          "blocknr %lu\n", bh->b_blocknr);
                  list_del(&record->hash);
                  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 && !bh->b_pprev) {
            struct buffer_head *bh2;
            bh2 = get_hash_table(bh->b_dev, bh->b_blocknr, bh->b_size);
            if (bh2) {
                  clear_bit(BH_Revoked, &bh2->b_state);
                  __brelse(bh2);
            }
      }
      
      return did_revoke;
}


/*
 * Write revoke records to the journal for all entries in the current
 * revoke hash, deleting the entries as we go.
 *
 * Called with the journal lock held.
 */

void journal_write_revoke_records(journal_t *journal, 
                          transaction_t *transaction)
{
      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;
      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;
                  write_one_revoke_record(journal, transaction,
                                    &descriptor, &offset, 
                                    record);
                  count++;
                  list_del(&record->hash);
                  kmem_cache_free(revoke_record_cache, record);
            }
      }
      if (descriptor) 
            flush_descriptor(journal, descriptor, offset);
      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 journal_head **descriptorp, 
                            int *offsetp,
                            struct jbd_revoke_record_s *record)
{
      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);
                  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     = htonl(JFS_MAGIC_NUMBER);
            header->h_blocktype = htonl(JFS_REVOKE_BLOCK);
            header->h_sequence  = htonl(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;
      }
      
      * ((unsigned int *)(&jh2bh(descriptor)->b_data[offset])) = 
            htonl(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)
{
      journal_revoke_header_t *header;

      if (is_journal_aborted(journal)) {
            JBUFFER_TRACE(descriptor, "brelse");
            __brelse(jh2bh(descriptor));
            return;
      }
      
      header = (journal_revoke_header_t *) jh2bh(descriptor)->b_data;
      header->r_count = htonl(offset);
      set_bit(BH_JWrite, &jh2bh(descriptor)->b_state);
      {
            struct buffer_head *bh = jh2bh(descriptor);
            BUFFER_TRACE(bh, "write");
            ll_rw_block (WRITE, 1, &bh);
      }
}

#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 long blocknr, 
                   tid_t sequence)
{
      struct jbd_revoke_record_s *record;
      
      record = find_revoke_record(journal, blocknr);
      if (record) {
            /* If we have multiple occurences, 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 long 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);
            }
      }
}


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